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C1, FM 5-410FM 5-410, change 1Prepared March 1997

Military Soils Engineering

Cover Letter

Table of Contents

List of Figures

List of Tables

Preface

Chapter 2

Chapter 7

Glossary

Authentication Page

C1, FM 5-410

Change 1 HeadquartersDepartment of the Army

Washington, DC,

Military Soils Engineering

1. Change FM 5-410, 23 December 1992, as follows:

Remove Old Pages Insert New Pagesi through xxix i through xxix

2-29 through 2-387-1 through 7-8 7-1a through 7-8

Glossary-29 through Glossary-30

2. A bar (\) marks new or changed material.

3. File this transmittal sheet in front of the publication.

DISTRIBUTION RESTRICTION: Approved for public release; distribution is unlim-ited.

By Order of the Secretary of the Army:

DENNIS J. REIMERGeneral, United States Army

Chief of Staff

Official:

DISTRIBUTION:

Active Army, USAR, and ARNG: To be distributed in accordance with DA Form 12-11-E, requirements for FM 5-410, Military Soils Engineering (Qty rqr blk no. 3832).

Field Manual 5-410 *FM 5-410Headquarters

Department of the ArmyWashington, DC, 23 December 1992

Military Soils Engineering

Contents

PageLIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xviLIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxviPREFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxix

CHAPTER 1. ROCKS AND MINERALS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1Section I. Minerals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

Physical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1Hardness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1Crystal form. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2Cleavage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2Fracture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3Luster and color . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3Streak. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3Specific gravity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3

Common rock-forming minerals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3Quartz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4Feldspars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4Micas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4Amphiboles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4Pyroxenes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4Olivine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4Chlorite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4Calcite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5Dolomite. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5Limonite. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5Clay minerals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5

Section II. Rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5Formation processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5

Igneous. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6Sedimentary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6Metamorphic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8

DISTRIBUTION RESTRICTION: Approved for public release; distribution is unlimited.

*This manual supersedes FM 5-541, 27 May 1986, and TM 5-545, 8 July 1971.

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PageClassification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9

Igneous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-10Granite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-12Felsite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-12Gabbro and diorite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-12Basalt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-12Obsidian . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-13Pumice. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-13Scoria. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-13

Sedimentary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-13Conglomerate and breccia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-14Sandstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-15Shale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-15Tuff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-15Limestones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-15Dolomite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-15Chert . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-15

Metamorphic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-16Slate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-16Schist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-16Gneiss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-16Quartzite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-17Marble . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-17

Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-17Field identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-17General categories. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-17

Foliated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-18Very fine-grained . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-20Coarse-grained . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-21

Engineering properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-21Toughness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-21Hardness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-22Durability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-22Crushed shape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-22Chemical stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-22Surface character . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-22Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-22

CHAPTER 2. STRUCTURAL GEOLOGYSection I. Structural features in sedimentary rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

Bedding planes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1Folds. . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3

Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4Symmetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4

Cleavage and schistosity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6Faults. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6

Recognition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7Terminology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7Types. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-8

Joints . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-8Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9

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PageSignificance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9

Strike and dip. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-10

Section II. Geologic maps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-11Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-11

Bedrock or aerial maps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-13Surficial maps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-13Special purpose maps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-13

Symbols. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-14Formations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-14Contacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-14Fault lines and fold axes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-14Attitudes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-14Cross sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-14

Outcrop patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-14Horizontal strata. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-19Inclined strata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-22Domes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-22Basins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-22Plunging folds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-22Faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-22

Normal and reverse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-22Thrust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-23

Intrusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-23Surficial deposits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-23

Section III. Engineering considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-23Rock distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-23Rock fragmentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-23Rock slides and slumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-24Weak rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-25Fault zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-25Groundwater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-25Road cut alignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-26Quarry faces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-26Rock deformation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-26Earthquakes (fault movements) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-26Dams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-29Tunnels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-29

Folded strata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-29Faulted strata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-30Groundwater problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-30

Bridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-30Buildings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-30Quarry operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-30

Section IV. Applied military geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-31Military geographic intelligence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-32

Maps and terrain models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-32Remote imagery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-32Terrain classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-32

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PageGeology in resolving military problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-32

Maps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-32Photographic interpretation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-34Reconnaissance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-34

Remote imagery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-34Field data collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-34

Boring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-36Exploration excavation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-36Geophysical exploration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-36

Equipment for field data collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-36Geological surveying. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-37

Pace-and-compass method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-37Plane-table-and-alidade method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-37Brunton-compass-and-aerial-photo method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-37Plane-table-, mosaic-, and-alidade method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-37Photogeology method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-37

CHAPTER 3. SURFICIAL GEOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1Fluvial process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

Drainage patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1Rectangular . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2Parallel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2Dendritic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2Trellis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2Radial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2Annular . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2Braided . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2

Density . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2Stream evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2

Youth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2Maturity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5Old age . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5

Stream deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6Point bars. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6Channel bars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-10Oxbow lakes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-10Natural levees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-10Backswamps/floodplains. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-14Alluvial terraces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-14Deltas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-14Alluvial fans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-17

Glacial process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-18Types of glaciation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-18

Continental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-18Alpine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-18

Glacial deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-18Stratified . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-18Unstratified . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-27

Eolian process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-28Types of eolian erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-30

Deflation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-30

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PageAbrasion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-30

Modes of transportation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-30Bed load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-30Suspended load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-30

Eolian features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-32Lag deposits or desert pavement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-32Sand dunes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-33Loess deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-35

Sources of construction aggregate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-36

CHAPTER 4. SOIL FORMATION AND CHARACTERISTICS . . . . . . . . . . . . . . . . . . 4-1Section I. Soil formation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1

Weathering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1Physical processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1

Unloading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1Frost action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1Organism growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2Temperature changes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2Crystal growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2Abrasion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2

Chemical processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2Oxidation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2Hydration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2Hydrolysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2Carbonation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2

Discontinuities and weathering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2Effects of climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3Effects on relief features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3Soil formation methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3

Residual soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3Transported soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3

Soil profiles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4Section II. Soil Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5

Physical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5Grain or particle size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6

Determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6Reports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7

Gradation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7Effective size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7Coefficient of uniformity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7Coefficient of curvature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7Well-graded soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7Poorly graded soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-10Bearing capacity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-10

Particle shape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-10Bulky . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-10Platy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-12Needlelike . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-12

Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-12

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PageSpecific gravity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-12Volume ratios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-12Weight ratios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-13

Relative density. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-14Soil-moisture conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-14

Adsorbed water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-15Plasticity and cohesion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-15Clay minerals and base exchange. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-16Capillary phenomena. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-16Shrinkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-17Swelling and slaking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-17Bulking of sands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-17

Consistency (Atterberg) limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-17Test procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-18

Liquid limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-18Plastic limit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-18

Plasticity index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-18

CHAPTER 5. SOIL CLASSIFICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1Section I. Unified Soil Classification System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1

Soil categories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1Course-grained soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2Fine-grained soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4Highly organic soils. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5

Laboratory testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5Desirable soil properties for roads and airfields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5

Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6Coarse-grained soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6Fine-grained soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6

Frost action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-13Compression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-13Drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-14Compaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-14

Desirable soil properties for embankments and foundations. . . . . . . . . . . . . . . . . . . 5-14Soil graphics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-17Field identification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-17

Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-17Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-18Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-18Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-19

Visual examination test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-19Breaking or dry strength test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-21Roll or thread test. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-22Ribbon test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-23Wet shaking test. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-23Odor test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-24Bite or grit test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-24Slaking test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-25Acid test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-25Shine test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-25Feel test. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-25

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PageHasty field identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-25

Optimum moisture content (OMC). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-29

Section II. Other soil classification systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-29Commonly used systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-29

Revised Public Roads System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-29Basis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-30Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-30

Agricultural Soil Classification System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-31Textural classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-31Pedological classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-31

Geological soil classification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-32Typical soil classification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-32

Unified Soil Classification System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-33Soil number 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-33Soil number 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-33Soil number 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-33Soil number 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-33

Revised Public Roads Classification System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-35Soil number 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-35Soil number 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-35Soil number 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-35Soil number 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-36

Agricultural Soil Classification System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-36Soil number 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-36Soil number 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-36Soil number 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-36Soil number 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-36

Comparison of classification systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-36

CHAPTER 6. CONCEPTS OF SOIL ENGINEERING . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1Section I. Settlement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1

Factors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1Compressibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1

Compressive load behavior. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1Cohesionless soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2

Consolidation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2Cohesive soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2Consolidation tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2

Section II. Shearing resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3Importance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3Laboratory tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3California Bearing Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3Airfield Index (AI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4

Airfield cone penetrometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-5

Soil-strength evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-5Fine-grained soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-5

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PageCoarse-grained soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-6

Correlation between CBR and AI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-6

Section III. Bearing capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-7Importance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-7Foundations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-7

Shallow foundations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-7Deep foundations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-8

Piles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-8Piers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-9

Section IV. Earth-retaining structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-9Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-9Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-9

Retaining walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-9Backfills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-11Drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-11Frost action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-13Timber crib . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-13Other timber walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-14Gabions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-14

Excavation bracing system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-16Shallow excavations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-16Narrow shallow excavations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-16Wide shallow excavations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-17

CHAPTER 7. MOVEMENT OF WATER THROUGH SOILS . . . . . . . . . . . . . . . . . . . 7-1aSection I. Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1a

Hydrologic cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1aSurface water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1b

Streams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1bLakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1bSwamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1b

Springs and seeps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1bGravity springs and seeps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1bArtesian springs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1c

Groundwater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1cFree, or gravitational, water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1dHygroscopic moisture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1dCapillary moisture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1dLocating groundwater sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2

Hydrogeologic indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2Geologic indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2

Permeability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3Drainage characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-4

Well-drained soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-4Poorly drained soils. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-4Impervious soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-4

Filter design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-4Porosity and permeability of rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6

Porosity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6

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PagePermeability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6

Water table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6Perched water table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6Aquifer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6Saltwater intrusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-7

Section II. Frost action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-7Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-7

Freezing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-7Thawing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-7

Conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-10Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-12

Heaving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-12Loss of pavement strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-12

Rigid pavements (concrete) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-13Flexible bituminous pavements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-13Slopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-13

Investigational procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-13Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-14

Base composition requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-14Pavement design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-16

Control of surface deformation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-16Provision of adequate bearing capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-17

CHAPTER 8. SOIL COMPACTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1Section I. Soil properties affected by compaction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1

Advantages of soil compaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1Settlement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1Shearing resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-2Movement of water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-2Volume change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-2

Section II. Design considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-2Moisture-density relationships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-2

Compaction characteristics of various soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-3Other factors that influence density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-4Addition of water to soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-5Handling wet soils. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-6Variation of compactive effort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-6

Compaction specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-6CBR design procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-7Subgrade compaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-9

Expansive clays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-11Clays and organic soils. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-11Silts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-11

Base compaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-11Maintenance of soil density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-11

Section III. Construction Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-12General considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-12Selection of materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-12Dumping and spreading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-12

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PageCompaction of embankments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-15Density determinations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-15Field control of compaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-16

Determination of moisture content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-16Field examination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-16Field drying. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-16“Speedy” moisture content test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-17Nuclear densimeter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-17

Determination of water to be added . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-17Compaction equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-17

Pneumatic-tired roller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-18Pneumatic roller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-18Self-propelled, pneumatic-tired roller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-18Sheepsfoot roller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-19Tamping-foot roller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-20Steel-wheeled roller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-20Self-propelled, smooth-drum vibratory roller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-20Other equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-20

Compactor selection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-20Availability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-21Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-21

Section IV. Quality control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-21Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-21Quality-control plan. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-22

Lot size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-22Random sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-22Test tolerance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-22Penalty system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-23

Theater-of-operations quality control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-23Corrective actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-23

Overcompaction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-23Undercompaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-23Too wet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-24Too dry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-24

CHAPTER 9. SOIL STABILIZATION FOR ROADS AND AIRFIELDS . . . . . . . . . . . 9-1Section I. Methods of stabilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1

Basic considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1Mechanical stabilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-2

Uses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-3Objective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-3Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-3Soil base requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-4Soil surface requirements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-4Proportioning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-4

Use of local materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-4Blending . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-5Numerical proportioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-5Specified gradation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-5Graphical proportioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-5

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PageArithmetical proportioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-6Plasticity requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-8Field proportioning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-8

Waterproofing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-8Sources of water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-9Objectives of waterproofers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-9

Chemical admixture stabilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-10Cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-10

Modification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-11Stabilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-14

Lime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-18Modification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-19Stabilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-19Other additives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-21

Fly-ash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-21Class C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-21Class F. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-21Lime-fly ash mixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-21Lime-cement-fly ash (LCF) mixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-22

Bituminous materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-22Soil gradation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-22Types of bitumen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-22Mix design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-23

Section II. Design concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-26Structural categories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-26Stabilized pavement design procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-28Thickness design procedures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-29Roads . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9- 30

Single-layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-30Multilayer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-32

Airfields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-36Single-layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-36Multilayer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-42

Examples of design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-45Example 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-45Example 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-46Example 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-47Example 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-47Example 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-48Example 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-48

Theater-of-operations airfield considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-48Functions of soil stabilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-48Design requirements for strength improvement . . . . . . . . . . . . . . . . . . . . . . . . . . 9-51

Section III. Dust control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-54Effects of dust. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-54Dust formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-54Dust palliatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-55

Intensity of area use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-55Nontraffic areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-55

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PageOccasional-traffic areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-55Traffic areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-56

Topography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-56Soil type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-56Soil surface features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-56

Loose and dry or slightly damp soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-56Loose and wet or scurry soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-56Firm and dry or slightly damp soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-56Firm and wet soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-56

Climate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-56Dust-control methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-57

Agronomic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-57Grasses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-57Shelter belts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-57Rough tillage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-57

Surface penetrant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-57Bitumens. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-58Resins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-59Salts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-59Water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-60

Admix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-60In-place admixing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-60Off-site admixing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-61

Surface blanket . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-61Minerals (aggregates) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-62Prefabricated membrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-62Prefabricated mesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-62Bituminous liquid. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-62Polyvinyl acetate (DCA 1295) (without reinforcement) . . . . . . . . . . . . . . . . . 9-62Polyvinyl acetate (DCA 1295) (with reinforcement) . . . . . . . . . . . . . . . . . . . . . 9-63Polypropylene-asphalt membrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-63

Selection of dust palliatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-63Application rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-70Placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-70Dilution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-70Prewetting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-71Curing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-71

Dust control on roads and cantonment areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-71Dust control for heliports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-71Control of sand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-71

Fencing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-71Paneling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-75Bituminous materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-76Vegetative treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-76Mechanical removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-76Trenching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-77Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-77Blanket covers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-77Salt solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-77

Section IV. Construction procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-77

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PageMechanical soil stabilization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-77

On-site blending . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-77Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-77Addition of imported soil materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-78Mixing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-78Compaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-78

Off-site blending . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-78Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-78Addition of blended soil materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-78

Lime stabilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-78Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-78Spreading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-78Preliminary mixing, watering and curing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-78Final mixing and pulverization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-79Compaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-79Final curing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-79

Cement stabilization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-79Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-79Spreading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-79Mixing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-79Compaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-79Curing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-79

Fly-ash stabilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-79Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-79Spreading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-79Mixing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-80Compaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-80Curing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-80

Bituminous stabilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-80Traveling plant mixer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-80Rotary mixer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-80Blade mixing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-80

Central plant construction methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-81Storing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-81Mixing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-81Hauling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-81Placing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-81Compacting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-81Curing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-81

Surface waterproofing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-81Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-81Mixing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-81Compaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-81Membrane placement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-81

CHAPTER 10. SLOPE STABILIZATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1Geologic features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1

Faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1Bedding plane slope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-2

Soil mechanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-2Slope gradient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-2

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PageNormal force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-3Downslope force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-3Shear strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-3

Groundwater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-7Uplift force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-7Seepage force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-8

Slope failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-8Rockfalls and rockslides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-8Debris avalanches and debris flows. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-10Slumps and earthflows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-11Surface drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-12Groundwater level. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-12Rock riprap or buttresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-13Interceptor drain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-14Fills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-14

Soil creep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-14Stable slope construction in bedded sediments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-16

Sandstone - Type I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-16Unstable-slope indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-18Road-location techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-18Construction techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-18

Sandstone - Type II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-20Unstable-slope indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-20Road-location techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-21Construction techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-21

Deeply weathered siltstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-21Unstable-slope indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-21Road-location techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-22Construction techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-22

Sandstone adjoining ridges of igneous rock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-22Unstable-slope indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-22Road-location techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-22Construction techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-22

CHAPTER 11. GEOTEXTILES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-1Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-1

Reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-1Separation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-2

Bypass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-2Remove and replace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-2Build on directly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-2Stabilize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-2

Drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-2Filtration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-2

Unpaved aggregate road design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-3Site reconnaissance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-3Subgrade soil type and strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-3Subgrade soil permissable load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-3Wheel loads, contact pressure, and contact area . . . . . . . . . . . . . . . . . . . . . . . . . . 11-3Aggregate base thickness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-4

Aggregate quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-5

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PageService life. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-5

Selecting a geotextile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-5Roadway construction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-8

Prepare the site . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-8Lay the fabric . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-8Lay the base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-8

Earth retaining walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-9Construction on sand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-9

Procedures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-12Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-12

CHAPTER 12. SPECIAL SOIL PROBLEMS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-1Aggregate behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-1Soil-aggregate mixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-1Laterites and lateritic soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-1

Laterites. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-2Lateritic soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-2Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-2Profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-2Engineering classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-2Compacted soil characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-2Pavement construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-3

Subgrade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-3Base course . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-3Subbase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-3Surfacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-4Stabilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-4

Slopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-5Coral. . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-5

Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-5Pit-run coral . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-5Coral rock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-5Coral sand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-5

Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-5Uses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-6

Fills, subgrades, and base courses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-6Surfacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-6Concrete aggregate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-6

Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-6Desert soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-6Arctic and subarctic soils. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-7

Surface thawing index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-7Ecological impact of construction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-13

APPENDIX A. CBR DESIGN METHODOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1APPENDIX B. AVAILABILITY OF FLY ASH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1APPENDIX C. HAZARDS OF CHEMICAL STABILIZERS . . . . . . . . . . . . . . . . . . . . C-1GLOSSARY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Glossary-1REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References-1INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Index-1

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Preface

SCOPE

Construction in the theater of operations is normally limited to roads, airfields, andstructures necessary for military operations. This manual emphasizes the soils engineeringaspects of road and airfield construction. The references give detailed information on othersoils engineering topics that are discussed in general terms. This manual provides adiscussion of the formation and characteristics of soil and the system used by the UnitedStates (US) Army to classify soils. It also gives an overview of classification systems used byother agencies. It describes the compaction of soils and quality control, settlement andshearing resistance of soils, the movement of water through soils, frost action, and thebearing capacity of soils that serve as foundations, slopes, embankments, dikes, dams, andearth-retaining structures. This manual also describes the geologic factors that affect theproperties and occurrences of natural mineral/soil construction materials used to builddams, tunnels, roads, airfields, and bridges. Theater-of-operations construction methods areemphasized throughout the manual.

PURPOSE

This manual supplies engineer officers and noncommissioned officers with doctrinaltenets and technical facts concerning the use and management of soils during militaryconstruction. It also provides guidance in evaluating soil conditions, predicting soil behaviorunder varying conditions, and solving soil problems related to military operations. Militarycommanders should incorporate geologic information with other pertinent data whenplanning military operations, to include standing operating procedures.

The proponent of this publication is the US Army Engineer School. Submit changes forimproving this publication on DA Form 2028 and forward it to: Commandant, US ArmyEngineer School, ATTN: ATSE-TD-D, Fort Leonard Wood, MO 65473-6650.

Unless otherwise stated, masculine nouns and pronouns do not refer exclusively to men.

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LIST OF FIGURES

PageFigure 1-1. Crystal forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

Figure 1-2. Cleavage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

Figure 1-3. Fractures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3

Figure 1-4. The rock cycle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7

Figure 1-5. Intrusive and extrusive rock bodies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7

Figure 1-6. Cross section of igneous rock. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8

Figure 1-7. Bedding planes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9

Figure 1-8. Contact metamorphism zone. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9

Figure 1-9. Metamorphic foliation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-10

Figure 1-10. Jointing in igneous rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-12

Figure 1-11. Cross bedding in sandstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-14

Figure 1-12. Metamorphism of existing rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-18

Figure 1-13. Crushed shape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-22

Figure 2-1. The major plates of the earth’s crust. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2

Figure 2-2. Major features of the plate tectonic theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3

Figure 2-3. Location of rock outcrops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3

Figure 2-4. Folding of sedimentary rock layers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4

Figure 2-5. Common types of folds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5

Figure 2-6. Topographic expression of plunging folds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5

Figure 2-7. Fold symmetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6

Figure 2-8. Faulting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7

Figure 2-9. Fault zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7

Figure 2-10. Thrust fault with drag folds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-8

Figure 2-11. Fault terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-8

Figure 2-12. Types of faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9

Figure 2-13. Graben and horst faulting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9

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PageFigure 2-14. Jointing in sedimentary and igneous rock . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-10

Figure 2-15. Strike. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-11

Figure 2-16. Dip. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-11

Figure 2-17. Measuring strike and dip with a Brunton compass . . . . . . . . . . . . . . . . . . . . 2-12

Figure 2-18. Strike and dip symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-12

Figure 2-19. Strike and dip symbols of sedimentary rocks . . . . . . . . . . . . . . . . . . . . . . . . . 2-13

Figure 2-20. Symbolic patterns for rock types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-17

Figure 2-21. Geologic map symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-18

Figure 2-22. Placement of strike and dip symbols on a geologic map. . . . . . . . . . . . . . . . . 2-19

Figure 2-23. Geologic map and cross section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-19

Figure 2-24. Outcrop patterns of horizontal strata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-20

Figure 2-25. Outcrop patterns of inclined strata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-20

Figure 2-26. Outcrop patterns of an eroded dome . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-20

Figure 2-27. Outcrop patterns of an eroded basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-20

Figure 2-28. Outcrop patterns of plunging folds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-21

Figure 2-29. Outcrop patterns produced by faulting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-21

Figure 2-30. Outcrop patterns of intrusive rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-21

Figure 2-31. Outcrop patterns of surficial deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-21

Figure 2-32. Ripping in the direction of dip. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-24

Figure 2-33. Rock drills. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-24

Figure 2-34. Rock slide on inclined bedding plane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-25

Figure 2-35. Rules of thumb for inclined sedimentary rock cuts. . . . . . . . . . . . . . . . . . . . . 2-25

Figure 2-36. Road cut alignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-27

Figure 2-37. Quarry in the direction of strike . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-28

Figure 3-1. Typical drainage patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3

Figure 3-2. Topographic expression of a braided stream. . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4

Figure 3-3. Stream evolution and valley development. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5

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PageFigure 3-4. A youthful stream valley . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7

Figure 3-5. A mature stream valley . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-8

Figure 3-6. An old age stream valley . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-9

Figure 3-7. Meander erosion and deposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-10

Figure 3-8. Point bar deposits designated by gravel symbols . . . . . . . . . . . . . . . . . . . . . . 3-11

Figure 3-9. Channel bar deposits, oxbow lakes, and backswamp/floodplaindeposits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-12

Figure 3-10. Meander development and cutoff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-13

Figure 3-11. Oxbow lake deposits, natural levees, and backswamp deposits . . . . . . . . . . . 3-13

Figure 3-12. Alluvial terraces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-14

Figure 3-13. Topographic expression of alluvial terraces . . . . . . . . . . . . . . . . . . . . . . . . . . 3-15

Figure 3-14. Growth of a simple delta . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-16

Figure 3-15. Arcuate, bird’s-foot, and elongate deltas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-16

Figure 3-16. Alluvial fan and coalescing alluvial fans . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-17

Figure 3-17. Cedar Creek alluvial fan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-19

Figure 3-18. Coalescing alluvial fans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-20

Figure 3-19. Major floodplain features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-21

Figure 3-20. World distribution of fluvial landforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-22

Figure 3-21. Ice sheets of North America and Europe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-23

Figure 3-22. Continental glaciation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-24

Figure 3-23. Alpine glaciation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-25

Figure 3-24. Moraine topographic expression with kettle lakes, swamps, andeskers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-26

Figure 3-25. Valley deposits from melting ice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-27

Figure 3-26. Idealized cross section of a drumlin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-28

Figure 3-27. Topographic expression of a drumlin field. . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-29

Figure 3-28. Distribution of major groups of glacial landforms across theUnited States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-30

Figure 3-29. World distribution of glacial landforms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-31

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PageFigure 3-30. Three stages illustrating the development of desert armor. . . . . . . . . . . . . . . 3-32

Figure 3-31. Cutting of a ventifact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-33

Figure 3-32. Eolian features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-33

Figure 3-33. Sand dune types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-34

Figure 3-34. Loess landforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-35

Figure 3-35. Topographic expression of sand dunes and desert pavement . . . . . . . . . . . . . 3-36

Figure 3-36. Worldwide distribution of eolian landforms . . . . . . . . . . . . . . . . . . . . . . . . . . 3-37

Figure 4-1. Residual soil forming from the in-place weathering of igneousrock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4

Figure 4-2. Soil profile showing characteristic soil horizons . . . . . . . . . . . . . . . . . . . . . . . 4-5

Figure 4-3. Dry sieve analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6

Figure 4-4. Data sheet, example of dry sieve analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-8

Figure 4-5. Grain-size distribution curve from sieve analysis. . . . . . . . . . . . . . . . . . . . . . . 4-9

Figure 4-6. Well-graded soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-10

Figure 4-7. Uniformly graded soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-10

Figure 4-8. Gap-graded soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-10

Figure 4-9. Typical grain-size distribution curves for well-graded andpoorly graded soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-11

Figure 4-10. Bulky grains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-11

Figure 4-11. Volume-weight relationships of a soil mass . . . . . . . . . . . . . . . . . . . . . . . . . . 4-12

Figure 4-12. Layer of adsorbed water surrounding a soil particle . . . . . . . . . . . . . . . . . . . 4-15

Figure 4-13. Capillary rise of water in small tubes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-16

Figure 4-14. U-shaped compaction curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-18

Figure 4-15. Liquid limit test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-18

Figure 5-1. Sample plasticity chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3

Figure 5-2. Graphical summary of grain-size distribution . . . . . . . . . . . . . . . . . . . . . . . . 5-20

Figure 5-3. Breaking or dry strength test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-22

Figure 5-4. Roll or thread test. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-22

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PageFigure 5-5. Ribbon test (highly plastic clay) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-23

Figure 5-6. Wet shaking test. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-24

Figure 5-7. Suggested procedure for hasty field identification. . . . . . . . . . . . . . . . . . . . . 5-26

Figure 5-7. Suggested procedure for hasty field identification (continued) . . . . . . . . . . . . 5-27

Figure 5-7. Suggested procedure for hasty field identification (continued) . . . . . . . . . . . . 5-28

Figure 5-8. Group index formula and charts, Revised Public Roads System . . . . . . . . . . 5-31

Figure 5-9. Relationship between LL and PI silt-clay groups, Revised PublicRoads System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-32

Figure 5-10. US Department of Agriculture textural classification chart . . . . . . . . . . . . . . 5-33

Figure 6-1. Laboratory shear tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

Figure 6-2. Correlation of CBR and AI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-7

Figure 6-3. Typical failure surfaces beneath shallow foundations . . . . . . . . . . . . . . . . . . . 6-7

Figure 6-4. Bearing piles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-8

Figure 6-5. Principal types of retaining walls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-10

Figure 6-6. Common types of retaining-wall drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-12

Figure 6-7. Eliminating frost action behind retaining walls . . . . . . . . . . . . . . . . . . . . . . 6-13

Figure 6-8. Typical timber crib retaining wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-14

Figure 6-9. Other timber retaining walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-15

Figure 6-10. Typical gabion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-15

Figure 6-11. Bracing a narrow shallow excavation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-16

Figure 6-12. Bracing a wide shallow excavation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-17

Figure 7a. Hydrologic cycle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1b

Figure 7b. Artesian groundwater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1c

Figure 7c. Groundwater zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1d

Figure 7-1. Capillary rise of moisture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1e

Figure 7-2. Base drains in an airfield pavement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1g

Figure 7-3. Typical subgrade drainage installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2

Figure 7-4. Mechanical analysis curves for filter material. . . . . . . . . . . . . . . . . . . . . . . . . . 7-5

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PageFigure 7-4a. Porosity in rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6

Figure 7-5. Determination of freezing index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-9

Figure 7-6. Formation of ice crystals on frost line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-10

Figure 7-7. Sources of water that feed growing ice lenses . . . . . . . . . . . . . . . . . . . . . . . . . 7-15

Figure 8-1. Typical moisture-density relationship . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-3

Figure 8-2. Moisture-density relationships of seven soils . . . . . . . . . . . . . . . . . . . . . . . . . . 8-5

Figure 8-3. Moisture-density relationships of two soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-7

Figure 8-4. Density, compaction, and moisture content. . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-8

Figure 8-5. Density and moisture determination by CBR design method . . . . . . . . . . . . 8-10

Figure 8-6. Self-propelled, pneumatic-tired roller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-18

Figure 8-7. Compaction by a sheepsfoot roller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-19

Figure 8-8. Two-axle, tandem steel-wheeled roller. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-20

Figure 8-9. Self-propelled, smooth-drum vibratory roller . . . . . . . . . . . . . . . . . . . . . . . . . 8-20

Figure 8-10. Use of test strip data to determine compactor efficiency . . . . . . . . . . . . . . . . . 8-21

Figure 9-1. Graphical method of proportioning two soils to meet gradationrequirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-7

Figure 9-2. Arithmetical method of proportioning soils to meet gradationrequirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-7

Figure 9-3. Graphical method of estimating plasticity characteristics . . . . . . . . . . . . . . . . 9-9of a combination of two soils

Figure 9-4. Gradation triangle for use in selecting a stabilizing additive . . . . . . . . . . . . 9-12

Figure 9-5. Group index for determining average cement requirements. . . . . . . . . . . . . . 9-17

Figure 9-6. Alternate method of determining initial design lime content. . . . . . . . . . . . . 9-20

Figure 9-7. Classification of aggregates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-25

Figure 9-8. Approximate effective range of cationic and anionic emulsionof various types of asphalt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-25

Figure 9-9. Determination of asphalt grade for expedient construction . . . . . . . . . . . . . . 9-26

Figure 9-10. Selection of asphalt cement content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-26

Figure 9-11. Typical sections for single-layer and multilayer design . . . . . . . . . . . . . . . . . 9-27

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PageFigure 9-12. Design curve for Class A and Class B single-layer

roads using stabilized soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-31

Figure 9-13. Design curve for Class C single-layer roads using stabilized soils . . . . . . . . . 9-31

Figure 9-14. Design curve for Class D single-layer roads using stabilized soils . . . . . . . . . 9-31

Figure 9-15. Design curve for Class E single-layer roads using stabilized soils . . . . . . . . . 9-32

Figure 9-16. Design curve for Class A and Class B multilayer roadsusing stabilized soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-33

Figure 9-17. Design curve for Class C multilayer roads using stabilized soils . . . . . . . . . . 9-33

Figure 9-18. Design curve for Class D multilayer roads using stabilized soils . . . . . . . . . . 9-34

Figure 9-19. Design curve for Class E multilayer roads using stabilized soils . . . . . . . . . . 9-34

Figure 9-20. Equivalency factors for soils stabilized with cement, lime,or cement and lime mixed with fly ash. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-36

Figure 9-21. Design curves for single-layer airfields using stabilized soilsin close battle areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-38

Figure 9-22. Design curves for single-layer airfields using stabilized soilsin rear areas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-39

Figure 9-23. Design curves for single-layer airfields using stabilized soilsin rear area 6,000’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-40

Figure 9-24. Design curves for single-layer airfields using stabilized soilsin tactical rear area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-40

Figure 9-25. Design curves for single-layer airfields using stabilized soilsin tactical COMMZ areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-41

Figure 9-26. Design curves for single-layer airfields using stabilized soilsin liaison COMMZ airfields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-42

Figure 9-27. Design curves for single-layer airfields using stabilized soilsin COMMZ. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-43

Figure 9-28. Design curves for single-layer airfields using stabilized soilsin semipermanent COMMZ airfields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-44

Figure 9-29. Thickness design procedure for subgrades that increase instrength with depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-53

Figure 9-30. Thickness design procedure for subgrades that decrease instrength with depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-54

Figure 9-31. Polypropylene membrane layout for tangential sections . . . . . . . . . . . . . . . . . 9-64

Figure 9-32. Polypropylene membrane layout for curved sections . . . . . . . . . . . . . . . . . . . 9-64

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PageFigure 9-33. Dust control effort required for heliports. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-73

Figure 9-34. Cross section of dune showing initial and subsequent fences. . . . . . . . . . . . . 9-75

Figure 9-35. Three fences installed to control dune formation . . . . . . . . . . . . . . . . . . . . . . 9-75

Figure 9-36. Three types of solid fencing or paneling for controlof dune formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-76

Figure 9-37. Schematic of dune destruction or stabilization by selectivetreatment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-77

Figure 10-1. Slope of bedding planes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-2

Figure 10-2. Normal force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-4

Figure 10-3. Downslope or driving force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-5

Figure 10-4. Frictional resistance to sliding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-6

Figure 10-5. Frictional resistance to sliding with uplift force of groundwater. . . . . . . . . . 10-9

Figure 10-6. Fricitonal resistance to sliding with and without groundwater . . . . . . . . . . 10-9

Figure 10-7. Debris avalanche . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-11

Figure 10-8. Backward roation of a slump block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-12

Figure 10-9. Jackstrawed trees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-12

Figure 10-10. Structural features of a slump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-13

Figure 10-11. Road construction across short slopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-13

Figure 10-12. Increasing slope stability with surface drainage . . . . . . . . . . . . . . . . . . . . . 10-14

Figure 10-13. Using rock riprap to provide support for road cuts or fills. . . . . . . . . . . . . . 10-15

Figure 10-14. Installing interceptor drains along an existing road . . . . . . . . . . . . . . . . . . 10-15

Figure 10-15. Building a road on a blanket . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-16

Figure 10-16. Block diagram of a Type I site . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-17

Figure 10-17. Topographic map of Type I site . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-18

Figure 10-18. Pistol-butted trees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-19

Figure 10-19. Tipped trees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-19

Figure 10-20. Tension cracks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-19

Figure 10-21. Safe disposal site . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-20

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PageFigure 11-1. Comparison of aggregate depth requirements with and

without a geotextile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-1

Figure 11-2. Effect of pumping action on base course. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-2

Figure 11-3. Separating a weak subgrade from a granular subbasewith a geofabric . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-2

Figure 11-4. Determining the soil’s shear strength by converting CBR valueor Cone Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-3

Figure 11-5. Thickness design curve for single-wheel load on gravel surfacedpavements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-7

Figure 11-6. Thickness design curve for dual-wheel load on gravel surfacedpavements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-7

Figure 11-7. Thickness design curve for tandem-wheel load on gravel-surfaced pavements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-8

Figure 11-8. Construction sequence using geotextiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-11

Figure 11-9. Constructing an earth retaining wall using geofabrics . . . . . . . . . . . . . . . . 11-13

Figure 11-10. Sand grid. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-14

Figure 12-1. Maximum depth to permafrost below a road after 5 yearsin a subarctic region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-8

Figure 12-2. Thickness of base required to prevent thawing of subgrade . . . . . . . . . . . . . . 12-9

Figure 12-3. Distribution of mean air thawing indexes (o)—North America. . . . . . . . . . . 12-10

Figure 12-4. Distribution of mean air thawing indexes (o)—Northern Eurasia . . . . . . . . 12-11

Figure 12-5. Distribution of mean air thawing index values for pavementsin North America (o) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-12

Figure 12-6. Determining the depth of thaw beneath pavements withgravel bases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-13

Figure 12-7. Determining the depth of freeze beneath pavements withgravel bases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-14

Figure 12-8. Permafrost degradation under different surface treatments. . . . . . . . . . . . . 12-15

Figure A-1. CBR design flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-2

Figure A-1. CBR design flowchart (continued) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-3

Figure A-2. Grain size distribution of Rio Meta Plain soil . . . . . . . . . . . . . . . . . . . . . . . . . A-7

Figure A-3. Plasticity chart plotted with Rio Meta Plain soil data . . . . . . . . . . . . . . . . . . . A-8

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PageFigure A-4. Density-moisture curve for Rio Meta Plain soil . . . . . . . . . . . . . . . . . . . . . . . . A-9

Figure A-5. Swelling curve for Rio Meta Plain soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-10

Figure A-6. CBR Family of Curves for Rio Meta Plain soil . . . . . . . . . . . . . . . . . . . . . . . . A-11

Figure A-7. Density-moisture curve for Rio Meta Plain soil with densityand moisture ranges plotted . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-12

Figure A-8. CBR Family of Curves for Rio Meta Plain soil with densityrange plotted . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-13

Figure A-9. Design CBR from Rio Meta Plain soil from CBR Familyof Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-14

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LIST OF TABLES

PageTable 1-1. The Mohs hardness scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

Table 1-2. Classification of igneous rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-11

Table 1-3. Classification of sedimentary rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-14

Table 1-4. Classification of metamorphic rocks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-16

Table 1-5. Identification of geologic materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-19

Table 1-6. Field-estimating rock hardness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-22

Table 1-7. Field-estimating rock density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-23

Table 1-8. Engineering properties of rocks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-24

Table 1-9. Aggregate suitability based on physical properties . . . . . . . . . . . . . . . . . . . . . 1-24

Table 1-10. Use of aggregates for military construction missions . . . . . . . . . . . . . . . . . . . 1-25

Table 2-1. Geologic time scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-15

Table 2-2. Reports for geographic/terrain intelligence . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-33

Table 2-3. Sources of remote imagery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-35

Table 3-1. Stream evolution process. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6

Table 3-2. Fluvial surficial features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-21

Table 3-3. Glacial surficial features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-32

Table 3-4. Aggregate types by feature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-38

Table 5-1. Unified soil classification (including identification and description) . . . . . . . 5-7

Table 5-2. Auxiliary laboratory identification procedure . . . . . . . . . . . . . . . . . . . . . . . . . . 5-9

Table 5-3. Characteristics pertinent to roads and airfields . . . . . . . . . . . . . . . . . . . . . . . 5-11

Table 5-4. Characteristics pertinent to embankment and foundationconstruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-15

Table 5-5. Comparison of the USCS, Revised Public Roads System,and FAA System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-29

Table 5-6. Revised Public Roads System of soil classification . . . . . . . . . . . . . . . . . . . . . 5-30

Table 5-7. Agricultural Soil Classification System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-34

Table 5-8. Classification of four inorganic soil types . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-35

Table 5-9. Comparison of soils under three classification systems . . . . . . . . . . . . . . . . . . 5-36

Table 7a. Hydrogeologic indicators for groundwater exploration . . . . . . . . . . . . . . . . . . . 7-3

Table 7-1. Frost-susceptible soil groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-11

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PageTable 8-1. Compaction test comparisons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-4

Table 8-2. Minimum compaction requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-8

Table 8-3. Soil classification and compaction requirements (average) . . . . . . . . . . . . . . . 8-13

Table 9-1. Numerical example of proportioning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-6

Table 9-2. Stabilization methods most suitable for specific applications . . . . . . . . . . . . . 9-11

Table 9-3. Guide for selecting a stabilizing additive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-13

Table 9-4. Minimum unconfined compressive strengths for cement, lime, andcombined lime-cement-fly ash stabilized soils . . . . . . . . . . . . . . . . . . . . . . . . . 9-14

Table 9-5. Durability requirements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-14

Table 9-6. Gradation requirements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-15

Table 9-7. Estimated cement requirements for various soil types . . . . . . . . . . . . . . . . . . . 9-15

Table 9-8. Average cement requirements for granular and sandy soils . . . . . . . . . . . . . . 9-16

Table 9-9. Average cement requirements for silty and clayey soils . . . . . . . . . . . . . . . . . . 9-16

Table 9-10. Average cement requirements of miscellaneous materials . . . . . . . . . . . . . . . . 9-18

Table 9-11. Recommended gradations for bituminous-stabilized subgradematerials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-23

Table 9-12. Recommended gradations for bituminous-stabilized base andsubbase materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-23

Table 9-13. Bituminous materials for use with soils of different gradations . . . . . . . . . . . 9-24

Table 9-14. Emulsified asphalt requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-24

Table 9-15. Thickness design procedures by airfield category . . . . . . . . . . . . . . . . . . . . . . 9-28

Table 9-16. Design determinations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-29

Table 9-17. Estimated time required for test procedures . . . . . . . . . . . . . . . . . . . . . . . . . . 9-29

Table 9-18. Road classifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-30

Table 9-19. Recommended minimum thickness of pavement and basecourse for roads in the theater-of-operations . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-35

Table 9-20. Reduced thickness criteria for permanent and nonexpedientroad and airfield design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-35

Table 9-21. Airfield categories. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-37

Table 9-22. Thickness reduction factors for Navy design . . . . . . . . . . . . . . . . . . . . . . . . . 9-45

Table 9-23. Equivalency factors for Air Force bases and Army airfields . . . . . . . . . . . . . . 9-45

Table 9-24. Recommended minimum thickness of pavements and basesfor airfields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-46

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PageTable 9-25. Stabilization functions pertinent to theater-of-operations

airfields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-49

Table 9-26. Basic airfield expedient surfacing requirements . . . . . . . . . . . . . . . . . . . . . . . 9-50

Table 9-27. Design requirements for strength improvement . . . . . . . . . . . . . . . . . . . . . . . . 9-52

Table 9-28. Recommended aggregate gradation for dust control on airfieldsand heliports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-62

Table 9-29. Dust palliative numbers for dust control in nontraffic areas . . . . . . . . . . . . . 9-65

Table 9-30. Dust palliative numbers for dust control in occasional-trafficareas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-66

Table 9-31. Dust palliative numbers for dust control in traffic areas . . . . . . . . . . . . . . . . 9-67

Table 9-32. Dust palliative electives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-68

Table 9-33. Roads and cantonment area treatments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-72

Table 9-34. Helipad/helicopter maintenance area treatments . . . . . . . . . . . . . . . . . . . . . . 9-74

Table 11-1. Vehicle input parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-4

Table 11-2. Boussinesq theory coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-5

Table 11-3. Compacted strength properties of common structural materials . . . . . . . . . . 11-6

Table 11-4. Criteria and properties for geotextile evaluation . . . . . . . . . . . . . . . . . . . . . . . 11-9

Table 11-5. Geotextile survivability for cover material and constructionequipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-10

Table 11-6. Minimum properties for geotextile survivability . . . . . . . . . . . . . . . . . . . . . . 11-10

Table 11-7. Recommended minimum overlap requirements. . . . . . . . . . . . . . . . . . . . . . . 11-12

Table 12-1. Gradation requirements for laterite and laterite gravels. . . . . . . . . . . . . . . . . 12-3

Table 12-2. Criteria for laterite base course materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-4

Table 12-3. Criteria for laterite subbase materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-4

Table 12-4. Measured depth of thaw below various surfaces in the subarcticafter 5 years. (Fairbanks, Alaska, mean annual temperature26 degrees Fahrenheit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-8

Table A-1. Recommended maximum permissible values of gradation andAtterberg limit requirements in subbases and select materials. . . . . . . . . . . . A-5

Table A-2. Desirable gradation for crushed rock, gravel, or slag anduncrushed sand and gravel aggregates for base courses . . . . . . . . . . . . . . . . . . A-5

Table B-1. Percentage of hard and brown coal reserves in major coal-producing countries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1

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CHAPTER 1

R o c k s a n d M i n e r a l s

The crust of the earth is made up of rock;rock, in turn, is composed of minerals. Thegeologist classifies rocks by determining theirmodes of formation and their mineral contentin addition to examining certain chemical andphysical properties. Military engineers use asimpler diagnostic method that is discussedbelow. Rock classification is necessary be-cause particular rock types have beenrecognized as having certain properties or asbehaving in somewhat predictable ways. Therock type implies information on manyproperties that serves as a guide in determin-ing the geological and engineeringcharacteristics of a site. This implied infor-mation includes—

A range of rock strength.Possible or expected fracture systems.The probability of encountering bed-ding planes.Weak zones.Other discontinuities.Ease or difficulty of rock excavation.Permeability.Value as a construction material.Trafficability.

This chapter describes procedures for fieldidentification and classification of rocks andminerals. It also explains some of the proces-ses by which rocks are formed. The primaryobjective of identifying rock materials andevaluating their physical properties is to beable to recommend the most appropriate ag-gregate type for a given military constructionmission.

Section I. Minerals

PHYSICAL PROPERTIESRocks are aggregates of minerals. To un-

derstand the physical properties of rocks, it isnecessary to understand what minerals are.A mineral is a naturally occurring, inorgani-cally formed substance having an orderedinternal arrangement of atoms. It is a com-pound and can be expressed by a chemicalformula. If the mineral’s internal frameworkof atoms is expressed externally, it forms acrystal. A mineral’s characteristic physicalproperties are controlled by its compositionand atomic structure, and these propertiesare valuable aids in rapid field identification.Properties that can be determined by simplefield tests are introduced here to aid in theidentification of mineralsthe identification of rocks.are—

Hardness.Crystal form.Cleavage.Fracture.Luster and color.Streak.

and indirectly inThese properties

Specific gravity.

HardnessThe hardness of a mineral is a measure of

its ability to resist abrasion or scratching byother minerals or by an object of known hard-ness. A simple scale based on empirical testshas been developed and is called the Mohs

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Hardness Scale. The scale consists of 10minerals arranged in increasing hardnesswith 1 being the softest. The 10 mineralsselected to form the scale of comparison arelisted in Table 1-1. Hardness kits containingmost of the reference minerals are available,but equivalent objects can be substituted forexpediency. Objects with higher values onMobs’ scale are capable of scratching objectswith lower values. For example, a rockspecimen that can be scratched by a coppercoin but not by the fingernail is said to have ahardness of about 3. Military engineersdescribe a rock as either hard or soft. A rockspecimen with a hardness of 5 or more is con-sidered hard. The hardness test should beperformed on a fresh (unweathered) surfaceof the specimen.

Crystal FormMost, but not all, minerals form crystals.

The form, or habit, of the crystals can be diag-nostic of the mineral and can help to identifyit. The minerals galena (a lead ore) and halite(rock salt) commonly crystallize as cubes.Crystals of garnet (a silicate mineral) com-monly have 12 or 24 equidimensional faces.Some minerals typically display long needle-like crystals. Minerals showing no crystalform are said to be amorphous. Figure 1-1 il-lustrates two of the many crystal forms.

Rocks and Minerals 1-2

CleavageCleavage is the tendency of a mineral to

split or separate along preferred planes whenbroken. It is fairly consistent from sample tosample for a given mineral and is a valuableaid in the mineral’s identification. Cleavageis described by noting the direction, the de-gree of perfection, and (for two or morecleavage directions) the angle of intersectionof cleavage planes. Some minerals have onecleavage direction; others have two or moredirections with varying degrees of perfection.Figure 1-2 illustrates a mineral with onecleavage direction (mica) and one with threedirections (calcite). Some minerals, such asquartz, form crystals but do not cleave.

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FractureFracture is the way in which a mineral

breaks when it does not cleave alongcleavage planes. It can be helpful in fieldidentification. Figure 1-3 illustrates the com-mon kinds of fracture. They are—

Conchoidal. This fracture surface ex-hibits concentric, bowl-shaped struc-tures like the inside of a clam shell(for example, chert or obsidian).Fibrous or splintery. This fracture sur-face shows fibers or splinters (forexample, some serpentine).Hackly. This fracture surface hassharp, jagged edges (for example,shist).Uneven. This fracture surface isrough and irregular (for example, ba-salt).

Luster and ColorThe appearance of a mineral specimen in

reflected light is called its luster. Luster iseither metallic or nonmetallic. Common non-metallic lusters are—

Vitreous (having the appearance ofglass).Adamantine (having the brilliant ap-pearance of diamonds).Pearly (having the iridescence ofpearls).Silky (having a fibrous, silklike lus-ter).

Resinous (having the appearance ofresin).

For some minerals, especially the metallicminerals, color is diagnostic. Galena (leadsulphide) is steel gray, pyrite (iron sulphide)is brass yellow, and magnetite (an iron ore) isblack. However, many nonmetallic mineralsdisplay a variety of colors. The use of color inmineral identification must be madecautiously since it is a subjective determina-tion.

StreakThe color of a powdered or a crushed mineral

is called the streak. The streak is obtained byrubbing the rnineral on a piece of unglazed por-celain, called a streak plate. The streak ismuch more consistent in a mineral than thecolor of the intact specimen. For example, anintact specimen of the mineral hematite (aniron ore) may appear black, brown, or red, butthe streak will always be dark red. The streakis most useful for the identification of dark-colored minerals such as metallic sulfides andoxides. Minerals with hardness 6.5 will not ex-hibit a streak, because they are harder than apiece of unglazed porcelain.

Specific GravityThe specific gravity of a substance is the

ratio of its weight (or mass) to the weight (ormass) of an equal volume of water. In fieldidentification of minerals, the heft, or ap-parent weight, of the specimen is an aid to itsidentification. Specific gravity and heft arecontrolled by the kinds of atoms making upthe mineral and the packing density of theatoms. For example, ores of lead always haverelatively high specific gravity and feel heavy.

COMMON ROCK-FORMING MINERALSThere are approximately 2,000 known

varieties of minerals. Only about 200 arecommon enough to be of geologic andeconomic importance. Some of the more im-portant minerals to military engineers are—

Quartz.Feldspars.Micas.

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Amphiboles.Pyroxenes.Olivine.Chlorite.Calcite.Dolomite.Limonite.Clay.

QuartzQuartz (silicon dioxide) is an extremely

hard, transparent to translucent mineralwith a glassy or waxy luster. Colorless towhite or smoky-gray varieties are most com-mon, but impurities may produce many othercolors. Like man-made glass, quartz has aconchoidal (shell-like) fracture, often imper-fectly developed. It forms pointed, six-sidedprismatic crystals on occasion but occursmost often as irregular grains intergrownwith other minerals in igneous and metamor-phic rocks; as rounded or angular g-rains insedimentary rocks (particularly sandstones);and as a microcrystalline sedimentary rock orcementing agent. Veins of milky whitequartz, often quite large, fill cracks in manyigneous and metamorphic rocks. Unlikenearly all other minerals, quartz is virtuallyunaffected by chemical weathering.

FeldsparsFeldspars form very hard, blocky, opaque

crystals with a pearly or porcelainlike lusterand a nearly rectangular cross section. Crys-tals tend to cleave in two directions along flat,shiny, nearly perpendicular surfaces.Plagioclase varieties often have fine parallelgrooves (striations) on one cleavage surface.Orthoclase varieties are usually pink, red-dish, ivory, or pale gray. Where more thanone variety is present, color differences arenormally distinct. Crystalline feldspars aremajor components of most igneous rocks,gneisses, and schists. In the presence of airand water, the feldspars weather to clayminerals, soluble salts, and colloidal silica.

MicasMicas form soft, extremely thin, trans-

parent to translucent, elastic sheets andflakes with a bright glassy or pearly luster.

“Books” of easily separated sheets frequentlyoccur. The biotite variety is usually brown orblack, while muscovite is yellowish, white, orsilvery gray. Micas are very common ingranitic rocks, gneisses, and schists. Micasweather slowly to clay minerals.

AmphibolesAmphiboles (chiefly hornblende) are hard,

dense, glassy to silky minerals found chieflyin intermediate to dark igneous rocks andgneisses and schists. They generally occur asshort to long prismatic crystals with a nearlydiamond-shaped cross section. Dark green toblack varieties are most common, althoughlight gray or greenish types occur in somemarbles and schists. Amphiboles weatherrapidly to form chlorite and, ultimately, clayminerals, iron oxides, and soluble carbonates.

PyroxenesPyroxenes (chiefly augite) are hard, dense,

glassy to resinous minerals found chiefly indark igneous rocks and, less often, in darkgneisses and schists. They usually occur aswell- formed, short, stout, columnar crystalsthat appear almost square in cross section.Granular crystals are common in some verydark gabbroic rocks. Masses of nearly purepyroxene form a rock called pyroxenite.Colors of green to black or brown are mostcommon, but pale green or gray varietiessometimes occur in marbles or schists.Pyroxenes weather much like the am-phiboles.

OlivineOlivine is a very hard, dense mineral that

forms yellowish-green to dark olive-green orbrown, glassy grains or granular masses invery dark, iron-rich rocks, particularly gab-bro and basalt. Masses of almost pure olivineform a rare rock called peridotite. Olivineweathers rapidly to iron oxides and solublesilica.

ChloriteChlorite is a very soft, grayish-green to

dark green mineral with a pearly luster. Itoccurs most often as crusts, masses, or thin

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sheets or flakes in metamorphic rocks, par-ticularly schists and greenstone. Chloriteforms from amphiboles and pyroxenes byweathering or metamorphism and, in turn,weathers to clay minerals and iron oxides.

CalciteCalcite is a soft, usually colorless to white

mineral distinguished by a rapid bubblingor fizzing reaction when it comes in contactwith dilute hydrochloric acid (HC1). Calciteis the major component of sea shells andcoral skeletons and often occurs as well-formed, glassy to dull, blocky crystals. As arock-forming mineral, it usually occurs asfine to coarse crystals in marble, loose tocompacted granules in ordinary limestone,and as a cementing agent in many sedimen-tary rocks.

Calcite veins, or crack fillings, are commonin igneous and other rocks. Calcite weatherschiefly by solution in acidic waters or watercontaining dissolved carbon dioxide.

DolomiteDolomite is similar to calcite in appearance

and occurrence but is slightly harder andmore resistant to solutioning. It is distin-guished by a slow bubbling or fizzing reactionwhen it comes in contact with dilute HC1.Usually the reaction can be observed only ifthe mineral is first powdered (as by scrapingit with a knife). Coarse dolomite crystalsoften have curved sides and a pinkish color.Calcite and dolomite frequently occurtogether, often in intimate mixtures.

LimoniteLimonite occurs most often as soft,

yellowish-brown to reddish-brown, fine-grained, earthy masses or compact lumps orpellets. It is a common and durable cement-ing agent in sedimentary rocks and them majorcomponent of laterite. Most weathered rockscontain some limonite as a result of thedecomposition of iron-bearing minerals.

ClayClay minerals form soft microscopic flakes

that are usually mixed with impurities of

various types (particularly quartz, limonite,and calcite). When barely moistened, as bythe breath or tongue, clays give off a charac-teristic somewhat musty “clay” odor. Claysform a major part of most soils and of suchrocks as shale and slate. They are a commonimpurity in all types of sedimentary rocks.

Section II. Rocks

FORMATION PROCESSESA rock may be made of many kinds of

minerals (for example, granite containsquartz, mica, feldspar, and usuallyhornblende) or may consist essentially of onemineral (such as a limestone, which is com-posed of the mineral calcite). To the engineer,rock is a firm, hardened substance that, incontrast to soil, cannot be excavated by stand-ard earthmoving equipment. In reality, thereis a transitional zone separating rock and soilso that not all “rock” deposits require blast-ing. Some “rock” can be broken usingpowerful and properly designed rippingequipment. The geologist places less restric-tion on the definition of rock.

Rocks can be grouped into three broad clas-ses, depending on their origin. They are—

Igneous.Sedimentary.Metamorphic.

Igneous rocks are solidified products ofmolten material from within the earth’smantle. The term igneous is from a wordmeaning “formed by fire. ” Igneous rocks un-derlie all other types of rock in the earth’scrust and may be said to form the basement ofthe continents on which sedimentary rocksare laid down. Most sedimentary rocks areformed by the deposition of particles of olderrocks that have been broken down andtransported from their original positions bythe agents of wind, water, ice, or gravity.Metamorphic rocks are rocks that have beenaltered in appearance and physical propertiesby heat, pressure, or permeation by gases orfluids. All classes of rocks (sedimentary,igneous, and metamorphic) can bemetamorphosed. Igneous, sedimentary, and

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metamorphic rocks often occur in close as-sociation in mountainous areas, in areas onceoccupied by mountains but which have sinceeroded, and in broad, flat continental regionsknown as shields. Flat-lying sedimentaryrocks form much of the plains of the con-tinents and may occupy broad valleysoverlain by recent or active deposits of sedi-ments. The sediments being deposited intoday’s oceans, lakes, streams, floodplains,and deserts will be the sedimentary rocks oftomorrow. The rock-forming processes con-tinually interact in a scheme called the rockcycle, illustrated in Figure 1-4.

IgneousIgneous rocks are solidified from hot mol-

ten rock material that originated deep withinthe earth. This occurred either from magmain the subsurface or from lava extruded ontothe earth’s surface during volcanic eruptions.Igneous rocks owe their variations in physicaland chemical characteristics to differences inchemical composition of the original magmaand to the physical conditions under whichthe lava solidified.

The groups forming the subdivisions fromwhich all igneous rocks are classified are—

Intrusive igneous rocks (cooled frommagma beneath the earth’s surface).Extrusive igneous rocks (cooled frommagma on the earth’s surface).

Figure 1-5 is a block diagram illustratingthe major kinds of intrusive and extrusiverock bodies formed from the crystallization ofigneous rocks. Dikes and sills are tabular ig-neous intrusions that are thin relative totheir lengths and widths. Dikes are discor-dant; they cut across the bedding of the stratapenetrated. Sills are concordant; they in-trude parallel to and usually along beddingplanes or contacts of the surrounding strata.Dikes and sills may be of any geologic age andmay intrude young and old sediments.Batholiths are large, irregular masses of in-trusive igneous rock of at least 40 squaremiles in area. A stock is similar to a batholithbut covers less than 40 square miles in out-crop. Stocks and batholiths generallyincrease in volume (spread out) with depth

and originate so deep that their base usuallycannot be detected. Magma that reachesthe earth’s surface while still molten isejected onto the ground or into the air (orsea) to form extrusive igneous rock. Themolten rock may be ejected as a viscous liq-uid that flows out of a volcanic vent or fromfissures along the flanks of the volcano. Theflowing viscous mass is called lava and thelava flow may extend many miles from thecrater vent. Lava that is charged with gasesand ejected violently into the air formspyroclastic debris consisting of broken andpulverized rock and molten material. Thepyroclastics solidify and settle to the groundwhere they form deposits of ash and larger-sized material that harden into layered rock(tuff). Igneous rocks are usually durableand resistant and form ridges, caps, hills,and mountains while surrounding rockmaterial is worn away.

The chemical composition and thus themineral content of intrusive and extrusive ig-neous rocks can be similar. The differences inappearance between intrusive and extrusiverocks are largely due to the size and arrange-ment of the mineral grains or crystals. Asmolten material cools, minerals crystallizeand separate from solution. Silica-richmagma or lava solidifies into rocks high insilicon dioxide (quartz) and forms thegenerally light-colored igneous rocks. Moltenmaterial rich in ferromagnesian (iron-magnesium) compounds form the darker-colored igneous rocks, which are deficientin the mineral quartz. If the magma coolsslowly, large crystals have time to grow. Ifthe magma (or lava) cools quickly, large crys-tals do not have the chance to develop.Intrusive rocks are normally coarse-grainedand extrusive igneous rocks are fine-grainedfor this reason. If lava cools too quickly forcrystals to grow at all, then natural glassforms. Figure 1-6, page 1-8, illustrates thedifference between intrusive and extrusiveigneous rock crystals.

SedimentarySedimentary rocks, also called stratified

rocks, are composed of chemical precipitates,biological accumulations, or elastic particles.Chemical precipitates are derived from the

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decomposition of existing igneous, sedimen-tary, and metamorphic rock masses.Dissolved salts are then transported from theoriginal position and eventually become in-soluble, forming “precipitates”; or, throughevaporation of the water medium, they be-come deposits of “evaporites.” A relativelysmall proportion of the sedimentary rockmass is organic sediment contributed by theactivities of plants and animals. Clastic sedi-ments are derived from the disintegration ofexisting rock masses. The disintegratedrock is transported from its original posi-tion as solid particles. Rock particlesdropped from suspension in air, water, orice produce deposits of “elastic” sediments.Volcanically ejected material that istransported by wind or water and thendeposited forms another class of layered rockscalled “pyroclastics.” Most pyroclasticdeposits occur in the vicinity of a volcanicregion, but fine particles can be transportedby the wind and deposited thousands of milesfrom the source. Inorganic elastic sedimentsconstitute about three-fourths of thesedimentary rocks of the earth’s crust. Loosesediments are converted to rock by severalprocesses collectively known as lithification.These are—

Compaction.Cementation.Recrystallization.

The weight of overlying sediments thathave accumulated over a longtime producesgreat pressure in the underlying sediments.The pressure expels the water in the sedi-ments by the process of compaction and

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forces the rock particles closer together.Compaction by the weight of overlying sedi-ments is most effective in fine-grainedsediments like clay and silt and in organicsediments like peat. Cementation occurswhen precipitates of mineral-rich waters, cir-culating through the pores of sediments, fillthe pores and bind the grains together. Themost common cementing materials arequartz, calcite (calcium carbonate), and ironoxides (limonite and hematite). Recrystal-lization and crystal growth of calciumcarbonate dissolved in saturated lime sedi-ments develop rocks (crystalline limestone anddolomite) with interlocking, crystalline fabrics.

Sedimentary rocks are normally depositedin distinct parallel layers separated byabrupt, fairly even contact surfaces calledbedding planes. Each layer represents a suc-cessive deposit of material. Bedding planesare of great significance as they are planes ofstructural weakness. Masses of sedimentaryrock can move along bedding planes duringrock slides. Figure 1-7 represents the layer-cake appearance of sedimentary rock beds.Sedimentary rocks cover about 75 percent ofthe earth’s surface. Over 95 percent of thetotal volume of sediments consists of a varietyof shales, sandstones, and limestones.

MetamorphicThe alteration of existing rocks to

metamorphic rocks may involve the forma-tion within the rock of new structures,textures, and minerals. The major agents inmetamorphism are—

Temperature.Pressure.Chemically active fluids and gases.

Heat increases the solvent action of fluidsand helps to dissociate and alter chemicalcompounds. Temperatures high enough toalter rocks commonly result from the in-trusion of magma into the parent rock in theform of dikes, sills, and stocks. The zone of al-tered rock formed near the intrusion is calledthe contact metamorphism zone (see Figure1-8). The alteration zone may be inches tomiles in width or length and may grade

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laterally from the unaltered parent rock to thehighly metamorphosed derivative rock. Pres-sures accompanying the compressive forcesresponsible for mountain building in the upperearth’s crust produce regional metamorphicrocks characterized by flattened, elongated,and aligned grains or crystals that give the rocka distinctive texture or appearance called folia-tion (see Figure 1-9, page 1-10). Hot fluids,especially water and gases, are powerfulmetamorphic agents. Water under heat and

pressure acts as a solvent, promotes recrys-tallization, and enters into the chemicalcomposition of some of the altered minerals.

CLASSIFICATIONIgneous, metamorphic, and sedimentary

rocks require different identification andclassification procedures. The fabric, tex-ture, and bonding strength imparted to a rockby its formation process determine the proce-dures that must be used to classify it.

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IgneousIgneous rocks are classified primarily on

the basis of—Texture.Color (or mineral content).

Texture is the relative size and arrange-ment of the mineral grains making up therock. It is influenced by the rate of cooling ofthe molten material as it solidifies into rock.Intruded magmas cool relatively slowly andform large crystals if the intrusion is deep andsmaller crystals if the intrusion is shallow.Extrusive lava is exposed abruptly to the airor to water and cools quickly, forming smallcrystals or no crystals at all. Therefore, refer-ring to Table 1-2, igneous rocks may havetextures that are coarse-grained (mineralgrains and crystals that can be differen-tiated by the unaided eye), veryfine-grained (mineral crystals too small tobe differentiated by the unaided eye), or ofcontrasting grain sizes (large crystals, or

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“phenocrysts, “ in a fine-grained “groundmass”). The intrusive igneous rocks generallyhave a distinctive texture of coarse interlock-ing crystals of different minerals. Undercertain conditions, deep-seated intrusionsform “pegmatites” (rocks with very large crys-tals). The extrusive (volcanic) igneous rocks,however, show great variation in texture.Very fine-grained rocks maybe classified ashaving stony, glassy, scoriaceous, or fragmen-tal texture. A rock with a stony textureconsists of granular particles. Fine-grainedrocks with a shiny smooth texture showing aconchoidal fracture are said to be “glassy.”An example is obsidian, a black volcanicglass. Gases trapped in the extrusive lavamay escape upon cooling, forming bubblecavities, or vesicles, in the rock. The result is arock with scoriaceous texture. Fragmentalrocks are those compsed of lithified, pyroclas-tic material. The pyroclastic (volcanoclastic)deposits are made up of volcanic rock particles ofvarious sizes that have drifted and accumulatedby the action of wind and water after ejection

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from the volcanic vent. Fine-grained (smallerthan 32 millimeters (mm)) ejects (called lapil-li, or ash) form deposits that become volcanictuff. Lava flowing out of the volcanic vent orfissure forms a flow with a ropelike texture ifthe lava is very fluid. More viscous lava formsa blocky flow. Upon cooling, basaltic lavaflows, sills, and volcanic necks sometimescrack. They often acquire columnar joint-ing characterized by near-verticalcolumns with hexagonal cross sections(see Figure 1-10, page 1-12).

Igneous rocks are further grouped by theiroverall color, which is generally a result oftheir mineral content (see Table 1-2). The

light-colored igneous rocks are silica-rich,and the dark-colored igneous rocks aresilica-poor, with high ferromagnesian con-tent. The intermediate rocks show gradationsfrom light to dark, reflecting their mixed orgradational mineral content. An example il-lustrating the use of Table 1-2 is as follows:lava and other ejects charged with gases mayform scoria, a dark-colored, highly vesicularbasaltic lava or pumice, a frothy, light-coloredfelsite lava so porous that it floats on water.

The common igneous rocks are—Granite.Felsite.Gabbro and diorite.

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Basalt.Obsidian.Pumice.Scoria.

Granite. This is a coarsely crystalline, hard,massive, light-colored rock composed mainlyof potassium feldspar and quartz, usuallywith mica and/or hornblende. Commoncolors include white, gray, and shades of pinkto brownish red. Granite makes up most ofthe large intrusive masses of igneous rockand is frequently associated with (and maygrade into) gneisses and schists. In general,it is a reasonably hard, tough, and durablerock that provides good foundations, buildingstones, and aggregates for all types of con-struction. Relatively fine-grained varietiesare normally much tougher and more durablethan coarse-grained types, many of which dis-integrate rather rapidly under temperatureextremes or frost action. Very coarse-grainedand quartz-rich granites often bond poorlywith cementing materials, particularly as-phaltic cements. Antistripping agentsshould be employed when granite is used inbituminous pavements.

Felsite. This is a very fine-grained, usuallyextrusive equivalent of granite. Colors com-monly range from light or medium gray topink, red, buff, purplish, or light brownishgray. Felsites often contain scattered largecrystals of quartz or feldspar, Isolated gasbubbles and streaklike flow structures arecommon i n felsitic lavas. As a rule, felsitesare about as hard and dense as granites,but they are generally tougher and tend to

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splinter and flake when crushed. Most fel-sites contain a form of silica, which producesalkali-aggregate reactions with portland ce-ments. Barring these considerations, felsitescan provide good general-purpose aggregatesfor construction.

Gabbro and Diorite. They form a series ofdense, coarsely crystalline, hard, dark-colored intrusive rocks composed mainly ofone or more dark minerals along withplagioclase feldspar. Since gabbro anddiorite have similar properties and maybedifficult to distinguish in the field, they areoften grouped under the name gabbro-diorite.They are gray, green, brown, or black.Gabbro-diorites are common in smaller in-trusive masses, particularly dikes andsills. As a group, they make strong foun-dations and excellent aggregates for alltypes of construction. However, theirgreat toughness and high density makeexcavation and crushing costs very high,particularly in finer-grained varieties.

Basalt. This is a very fine-grained, hard,dense, dark-colored extrusive rock that oc-curs widely in lava flows around the world.Colors are usually dark gray to black,greenish black, or brown. Scattered coarsecrystals of olivine, augite, or plagioclase arecommon, as are gas bubbles that may or maynot be mineral-filled. With increasing grainsize, basalt often grades into diabase, an ex-tremely tough variety of gabbro. Both basaltand diabase make aggregates of the highestquality despite a tendency to crush into chipsor flakes in sizes smaller than 2 to 4 cen-timeters.

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Obsidian. This is a hard, shiny, usuallyblack, brown, or reddish volcanic glass thatmay contain scattered gas bubbles or visiblecrystals. Like man-made glass, it breaksreadily into sharp-edged flakes. Obsidian ischemically unstable, weak, and valueless as aconstruction material of any type.

Pumice. This is a very frothy or foamy,light-colored rock that forms over glassy orfelsitic lava flows and in blocks blown fromerupting volcanoes. Innumerable closelyspaced gas bubbles make pumice lightenough to float on water and also impart goodinsulating properties. Although highlyabrasive, pumice is very weak and canusually be excavated with ordinary handtools. It is used in the manufacture of low-strength, lightweight concrete and concreteblocks. Most varieties are chemically un-stable and require the use of low-alkaliportland cements.

Scoria. It looks very much like a coarse,somewhat cindery slag. In addition to itsfrothy texture, scoria may also exhibit stonyor glassy textures or a combination of both.The color of scoria ranges from reddish brownto dark gray or black. Scoria is somewhatdenser and tougher than pumice, and the gasbubbles that give it its spongy or frothy ap-pearance are generally larger and morewidely spaced than those in pumice. Scoriais very common in volcanic regions andgenerally forms over basaltic lava flows. It iswidely used as a lightweight aggregate in con-crete and concrete blocks. Like pumice, itmay require the use of special low-alkali ce-ments.

SedimentarySedimentary rocks are classified primarily

by—Grain size.Composition.

They can be described as either elastic or non-elastic (see Table 1-3, page 1-14). The elasticrocks are composed of discrete particles, orgrains. The nonclastic rocks are composed ofinterlocking crystals or are in earthy masses.

Clastic sedimentary rocks are further clas-sified as coarse-grained or fine-grained. Thecoarse-grained rocks have individual grainsvisible to the naked eye and includesandstones, conglomerates (rounded grains),and breccias (angular grains). These are therock equivalents of sands and gravels.The fine-grained rocks have individualgrains that can only be seen with the aidof a hand lens or microscope and includesilts tones, shales, clays tones, andmudstones.

Shales, claystones, and mudstones arecomposed of similar minerals and may besimilar in overall appearance; however, ashale is visibly laminated (composed of thintabular layers) and often exhibits “fissility,”that is, it can be split easily into thin sheets.Claystone and mudstone are not fissile.Mudstone is primarily a field term used totemporarily identify fine-grained sedimen-tary rocks of unknown mineral content.

The nonelastic sedimentary rocks can befurther described as inorganic (or chemical)or organic. Dolomite is an inorganic calcium-magnesium carbonate. Chert, a widespread,hard, durable sedimentary rock, composed ofmicrocrystalline quartz, precipitates fromsilica-rich waters and is often found in or withlimestones. Limestone is a calcium carbonatethat can be precipitated both organically andinorganically. A diagnostic feature of lime-stone is its effervescence in dilute HC1. Coalis an accumulation and conversion of the or-ganic remains of plants and animals undercertain environments.

Important features of the exposed orsampled portion of a deposit includestratification, the thickness of strata, theuniformity or nonuniformity of strata lat-erally, and the attitude (strike and dip) of thebedding planes. Special sedimentary bed-ding features are—

Cross bedding (individual layerswithin a bed lie at an angle to thelayers of adjacent beds (see Figure1-11, page 1-14), typical of sand duneand delta front deposits).

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Mud cracks (polygonal cracks in thesurface of dried-out mud flats).Ripple marks (parallel ridges in somesediments that indicate the directionof wind or water movement duringdeposition).

Some typical sedimentary rocks are—Conglomerate and breccia.

Chert.

Conglomerate and Breccia. They resem-ble man-made concrete in that they consist ofgravel-sized or larger rock fragments in afiner-grained matrix. Different varieties aregenerally distinguished by the size or com-position of the rock fragments (such aslimestone breccia, boulder conglomerate, or

Sandstone. quartz pebble conglomerate). Wide varia-Shale. tions in composition, degree of cementation,Tuff. and degree of weathering of component par-Limestone. titles make these rocks highly unpredictable,Dolomite. even within the same deposit. Generally,

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they exhibit poor engineering propertiesand are avoided in construction. Some veryweakly cemented types may be crushed foruse as fill or subbase material in road or air-field construction.

Sandstone. This is a medium- to coarse-grained, hard, gritty, elastic rock composedmainly of sand-sized (1/16 mm to 2 mm)quartz grains, often with feldspar, calcite, orclay. Sandstone varies widely in propertiesaccording to composition and cementation.Clean, compact, quartz-rich varieties, well-cemented by silica or iron oxides, generallyprovide good material for construction of alltypes. Low-density, poorly cemented, andclayey varieties lack toughness anddurability and should be avoided as sources ofconstruction material; however, some clay-free types may be finely crushed to providesand.

Shale. This is a soft to moderately hardsedimentary rock composed of very fine-grained silt and clay-sized particles as well asclay minerals. Silica, iron oxide, or calcite ce-ments may be present, but many shales lackcement and readily disintegrate or slakewhen soaked in water. Characteristically,shales form in very thin layers, break intothin platy pieces or flakes, and give off amusty odor when barely moistened. Oc-casionally, massive shales (called mudstones)occur, which break into bulky fragments.Shales are frequently interbedded withsandstones and limestones and, with increas-ing amounts of sand or calcite, may grade intothese rock types. Most shales can be ex-cavated without the need for blasting.Because of their weakness and lack ofdurability, shales make very poor construc-tion material.

Tuff. This is a low-density, soft to moder-ately hard pyroclastic rock composed mainlyof fine-grained volcanic ash. Colors rangefrom white through yellow, gray, pink, andlight brown to a rather dark grayish brown.When barely moistened, some tuffs give off aweak “clay” odor. Very compact varietiesoften resemble felsite but can usually be dis-tinguished by their softness and the presence

of glass or pumice fragments. Loose, chalkytypes usually feel rough and produce a grittydust, unlike the smooth particles of a truechalk or clay. Tuff is a weak, easily excavatedrock of low durability. When finely ground, ithas weak cementing properties. It is oftenused as an “extender” for portland cementand as a pozzolan to improve workability andneutralize alkali-aggregate reactions. It canalso be used as a fill and base course material.

Limestone. This is a soft to moderately hardrock composed mainly of calcite in the form ofshells, crystals, grains, or cementingmaterial. All varieties are distinguished by arapid bubbling or fizzing reaction when theycome in contact with dilute HC1. Colors nor-mally range from white through variousshades of gray to black; other colors mayresult from impurities. Ordinary limestone isa compact, moderately tough, very fine-grained or coarsely crystalline rock thatmakes a quality material for all constructionneeds. Hardness, toughness, and durabilitywill normally increase with greater amountsof silica cement. However, more than about30 percent silica may produce bondingproblems or alkali-aggregate reactions.Clayey varieties usually lack durability andtoughness and should be avoided. Weak, low-density limestones (including limerock andcoral) are weakly recemented when crushed,wetted, and compacted. They are widely usedas fill and base course material. In mildclimates, some may prove suitable for use inlow-strength portland cement concrete.

Dolomite. It is similar to limestone exceptthat the mineral dolomite occurs in lieu of cal-cite. It is distinguished by a slow bubbling orfizzing reaction when it comes into contactwith dilute HC1. Often the reaction cannot beseen unless the rock is first powdered (as byscraping with a knife). Limestone anddolomite exhibit similar properties, and oftenone grades into the other within a singledeposit.

Chert. This is a very hard, very fine-grainedrock composed of microcrystalline silicaprecipitated from seawater or groundwater.It occurs mainly as irregular layers or

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nodules in limestones and dolomites and aspebbles in gravel deposits or conglomerates.Most cherts are white to shades of gray. Verydark, often black, cherts are called flint,while reddish-brown varieties are calledjasper. Pure, unweathered cherts breakalong smooth, conchoidal (shell-like) surfaceswith a waxy luster; weathered or impureforms may seem dull and chalky-looking. Al-though cherts are very hard and tough, theyvary widely in chemical stability anddurability. Many produce alkali-aggregatereactions with portland cement, and most re-quire the use of antistripping agents withbituminous cements. Low-density chertsmay swell slightly when soaked and break upreadily under frost action. Despite theseproblems, cherts are used in road construc-tion in many areas where better materials arenot available.

MetamorphicMetamorphic rocks are classified primariIy

by—Mineral content.Fabric imparted by the agents ofmetamorphism.

They are readily divided into two descriptivegroups (see Table 1-4) known as—

Foliated.Nonfoliated.

Foliated metamorphic rocks display apronounced banded structure as a result ofthe reformational pressures to which theyhave been subjected. The nonfoliated, ormassive, metamorphic rocks exhibit no direc-tional structural features.

The common foliated or banded metamor-phic rocks include—

Slate.Schist.Gneiss.

Slate. This is a very fine-grained, compactmetamorphic rock that forms from shale. Un-like shale, slates have no “clay” odor. Theysplit into thin, parallel, sharp-edged sheets(or plates) usually at some angle to any ob-servable bedding. Colors are normally darkred, green, purple, or gray to black. Slates arewidely used as tiles and flagstones, but theirpoor crushed shape and low resistance tosplitting makes them unsuitable for ag-gregates or building stones.

Schist. This is a fine- to coarse-grained, well-foliated rock composed of discontinuous, thinlayers of parallel mica, chlorite, hornblende,or other crystals. Schists split readily alongthe structural layers into thin slabs or flakes.This characteristic makes schists un-desirable for construction use and hazardousto excavate. However, varieties intermediateto gneiss maybe suitable for fills, base cour-ses, or portland cement concrete.

Gneiss (pronounced “nice”). This is a roughlyfoliated, medium- to coarse-grained rock thatconsists of alternating streaks or bands. Thebanding is caused by segregation of light-colored layers of quartz and feldsparalternating with dark layers of ferromag-nesian minerals. These streaks may bestraight, wavy, or crumpled and of uniform or

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variable thickness. Gneisses normally breakinto irregular, bulky pieces and resemble thegranitic rocks in properties and uses. Withincreasing amounts of mica or more perfectlayering, gneisses grade into schists.

The common nonfoliated metamorphicrocks include—

Quartzite.Marble.

Quartzite. This is an extremely hard, fine-to coarse-grained, massive rock that formsfrom sandstone. It is distinguished fromsandstone by differences in fracture.Quartzite fractures through its componentgrains rather than around them as insandstone, because the cement and sandgrains of quartzite have been fused or weldedtogether during metamorphism. Therefore,broken surfaces are not gritty and often havea splintery or sugary appearance like that of abroken sugar cube or hard candy. Quartziteis one of the hardest, toughest, and mostdurable rocks known. It makes excellent con-struction material, but excavation andcrushing costs are usually very high. Be-cause of its high quartz content, antistrippingagents are normally required withbituminous cements, Even so, bonds may bepoor with very fine-grained types.

Marble. This is a soft, fine- to coarselycrystalline, massive metamorphic rock thatforms from limestone or dolomite. It is distin-guished by its softness, acid reaction, lack offossils, and sugary appearance on freshlybroken surfaces. Marble is similar to ordi-nary compact or crystalline limestones in itsengineering properties and uses. However,because of its softness, it is usually avoided asan aggregate for pavements on highways andairfields. White calcite or pinkish dolomiteveins and subtle swirls or blotches of trace im-purities give marble its typical veined or“marbled” appearance.

Metamorphic rocks have been derived fromexisting sedimentary, igneous, or metamor-phic rocks as depicted in Figure 1-4, page 1-7and Figure 1-12, page 1-18.

IDENTIFICATIONMilitary engineers must frequently select

the best rock for use in different types of con-struction and evaluate foundation orexcavation conditions.

Field IdentificationA simple method of identification of rock

types that can be applied in the field will as-sist in identifying most rocks likely to beencountered during military construction.This method is presented in simple terms forthe benefit of the field engineer who is notfamiliar with expressions normally used intechnical rock descriptions.

The identification method is based on acombination of simple physical and chemicaldeterminations. In some cases, the grainscomposing a rock may be seen, and the rockmay be identified from a knowledge of its com-ponents. In other cases, the rock maybe sofine-grained that the identification must bebased on its general appearance and theresults of a few easy tests.

The equipment required consists only of agood steel knife blade or a nail and a bottle ofdilute (10 percent solution) HC1, preferablywith a dropper. A small 6- to 10-power mag-nifying glass may also be helpful. HC1(muriatic acid) is available at most hardwarestores and through the military supply sys-tem. Military hospitals are a typical sourcefor HC1.

Samples for identification should be clean,freshly broken, and large enough to clearlyshow the structure of the rock. In a smallsample, key characteristics (such as anyalignment of the minerals composing therock) may not be observed as readily as in alarger one. Pieces about 3 inches by 4 inchesby 2 inches thick are usually suitable.

General CategoriesThe identification system of geologic

materials is given in flow chart form (seeTable 1-5, page 1-19). In this method, all con-siderations are based on the appearance or

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character of a clean, freshly broken, un-weathered rock surface. Weathered surfacesmay exhibit properties that may not be trueindicators of the actual rock type.

For most rocks the identification process isdirect and uncomplicated. If a positive iden-tification cannot be made, the more detailedrock descriptions (in the preceding para-graphs) should be consulted after first usingthe flow chart to eliminate all clearly inap-propriate rock types. By the use of des-criptive adjectives, a basic rock classificationcan be modified to buildup a “word picture” ofthe rock (for example, “a pale brown, fine-grained, thin-bedded, compact, clayey,silica-cemented sandstone”).

To use the flow chart, the sample must beplaced into one of three generalized groups

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based on physical appearance. These groupsare—

Foliated.Very fine-grained.Coarse-grained.

Foliated. Foliated rocks are those metamor-phic rocks that exhibit planar orientation oftheir mineral components. They may ex-hibit slaty cleavage (like slate) expressedby closely spaced fractures that cause thesample to split along thin plates. If thesample exhibits a parallel arrangement ofplaty minerals in thin layers and has asilky or metallic reflection, the sample hasschistosity and is called a schist. If thesample exhibits alternating streaks orbands of light and dark minerals of differ-ing composition, then the sample hasgneissic layering and is called a gneiss.

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Very Fine-Grained. If the sample appearspitted or spongy, it is called frothy. The pitsare called vesicles and are the result of hotgases escaping from magma at the top of alava pool. If the sample is light enough tofloat on water and is light-colored, it is calledpumice. If the frothy rock sample is dark-colored and appears cindery, it is calledscoria.

If the sample has the appearance of brokenglass, it is called either obsidian or quartz.Obsidian is a dark-colored natural volcanicglass that cooled too fast for any crystals todevelop. Quartz is not a glass but is identifiedon the flow chart as light-colored and glassy.Quartz is a mineral and not one of the ag-gregates classifed for use in militaryconstruction. It is often found in its crystal-line form with six-sided crystals. It iscommon as veins in both igneous andmetamorphic rock bodies.

A hardness test is conducted to determinewhether a stony sample is hard or soft. If thesample can be scratched with a knife or nail,then it is said to be soft. If it cannot bescratched, then it is said to be hard.

Fine-grained rocks maybe glassy, frothy, orstony. The term “stony” is used to differen-tiate them from “glassy” and “frothy” rocks.

If the sample is soft, a chemical determina-tion must be made using dilute HC1, HC1tests determine the presence or absence ofcalcite (calcium carbonate) which compriseslimestone/dolomite and marble. Very fine-grained rocks that are soft and stony inappearance and have an acid reaction arecomposed of calcium carbonate. If the sampleis dull and massive, it is called a limestone.Dolomites are also dull and massive and arenot separated from limestones on this chart,but they do not readily react to acid. Theirsurface must be powdered first by scratchingthe sample with a nail. The dolomite powderthen readily reacts to the acid. If the sampleexhibits a sugary appearance, then it is themetamorphic rock, marble. The sugary ap-pearance is due to the partial melting orfusing of calcite crystals by heat and pressure.

It is similar to the appearance of the sugarcoating on a breakfast cereal. These rocks aresusceptible to chem ical attack by acidic solu-tions that form when carbon dioxide (CO2) isabsorbed in groundwater. This produces amild carbonic acid that dissolves the calcite inthe rock. This is the process that producescaves and sinkholes. If there is not an acidreaction (no effervescence) and the samplehas a platy structure, it is a shale. A shalemay be any color. It is normally dull andseparates into soft, thin plates. When freshlybroken, it may have a musty odor similar toclay. Shales are derived from lithification ofclay particles and fine muds. Shale is asedimentary rock and should not be confusedwith its metamorphic equivalent, slate.Shales often occur interbedded within layersof limestone and dolomite. Because they areoften found with carbonate rocks, they mayexhibit an acid reaction due to contaminationby calcium carbonate.

If the sample has no acid reaction and has arelatively low density, with small pieces ofglass in its fine-grained matrix, the rock iscalled a tuff. Tuff is a volcanic sedimentaryrock comprised mostly of ash particles thathave been solidified. By the flow chart, it ischaracterized as soft; however, it may be hardif it has been welded by hot gases during theeruption. If it is hard, tuff may exhibit physi-cal properties that make it suitable for someconstruct ion applications.

Fine-grained, stony samples that are hardmay be waxy, dull, or sandy. Waxy samplesresemble candle wax and have a conchoidalfracture and sharp edges. These rocks arecalled chert. They often weather into soft,white materials. Dull samples are eitherlight- or dark-colored igneous extrusive rocks.If the sample is light-colored, it is a felsite.Felsites are normally massive but may ap-pear banded or layered. Unlike gneiss, thelayers are not made up of alternating lightand dark minerals. Felsites may also havecavities filled with other lighter-coloredminerals. They represent a variety of lavarocks that are high in silica. Because of theirgreat variety, they may be hard to identify

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properly. The dark counterpart to the felsitesis basalt. Basalt is normally black and verytough. It is also a lava rock and often exhibitscolumnar jointing. It often occurs as dikes orsills in other rock bodies.

Hard, sandy, very fine-grained samplescomposed mostly of quartz may be eithersandstone or quartzite. If the sample feelsgritty like sandpaper, it is called sandstone.Sandstones are sedimentary rocks composedof sand grains that have been cementedtogether. If the sample appears sugary anddoes not feel like sandpaper, the rock is calledquartzite. Quartzite is the metamorphicequivalent of sandstone. Like marble, it has asugary appearance, which is due to the par-tial melting and fusing of the crystal grains.

Coarse-Grained. Coarse-grained rocksrefer to those that have either crystals or ce-mented particles that are large enough to bereadily seen with the unaided eye. Samplesmay be hard or soft. Hard samples may ap-pear sandy, mixed, or fragmental. A sandysample would be a sandstone or a quartzite.Because coarse sands grade into fine sands,there are coarse sandstones and finesandstones. The sugary-appearing meta-morphic version of a coarse sandstone iscalled a quartzite.

Hard, coarse-grained rocks that are com-prised of mixed interlocking crystals have asalt-and-pepper appearance due to their lightand dark minerals. If the rock is predomi-nantly light in color, it is a granite. If it ispredominantly dark in color, it is called agabbro-diorite. Both of these rocks are ig-neous intrusive rocks that cooled slowly,allowing the growth of large interlockingcrystals. If the sample appears to be made ofround, cemented rock fragments similar tothe appearance of concrete, it is called a con-glomerate. If the rock fragments are angularinstead of round, the rock is called a breccia.

If a coarse-grained sample is soft, it mayeither be fragmental or have an acid reaction.If it appears fragmental and has a low densityand small pieces of glass, it is a tuff. Tuff has

already been described as a very fine-g-rained,stony, soft rock material. This entry on thechart is for the coarse-grained version of thesame material. The coarse-grained rocksamples that are soft and have an acid reac-tion are coarse-grained limestones andmarbles, as already described.

The system of identification of rock typesused by military engineers serves to identifymost common rock types. This method re-quires the user to approach rock identificationin a mnsistent and systematic manner; other-wise, important rock characteristics may gounnoticed. Many important rock featuresmay not appear in small hand specimens. Toenable better identification and evaluation,personnel who are in charge of geologic ex-ploration should maintain careful notes onsuch rock features as bedding, foliation,gradational changes in composition orproperties, and on the associations of rocks inthe field. During preliminary reconnaissancework, geologic maps or map substitutesshould be used to make preliminary engineer-ing estimates based on the typical rockproperties.

Engineering PropertiesThe following engineering properties and

tests are provided to help make engineeringjudgments concerning the use of rockmaterials as construction aggregate:

Toughness.Hardness.Durability.Crushed shape.Chemical stability.Surface character.Density.

Preliminary engineering estimates can bemade based on the typical rock properties as-certained from these tests. If a rock samplecannot be identified using the flow chart, adecision can be made as to its suitability foruse as a construction material by thesetests.

Toughness. This is mechanical strength, orresistance to crushing or breaking. In the

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field, this property may be estimated by at-tempting to break the rock with a hammer orby measuring its resistance to penetration byimpact drills.

Hardness. This is resistance to scratchingor abrasion. In the field, this may be es-timated by attempting to scratch the rockwith a steel knife blade. Soft materials arereadily scratched with a knife, while hardmaterials are difficult or impossible to scratch(see Table 1-6).

Durability. This is resistance to slaking ordisintegration due to alternating cycles ofwetting and drying or freezing and thawing.Generally, this may be estimated in the fieldby observing the effects of weathering onnatural exposures of the rock.

Crushed Shape. Rocks that break into ir-regular, bulky fragments provide the bestaggregates for construction because the par-ticles compact well, interlock to resistdisplacement and distribute loads, and are ofnearly equal strength in all directions. Rocksthat break into elongated pieces or thin slabs,sheets, or flakes are weak in their thin dimen-sions and do not compact, interlock, ordistribute loads as effectively (see Figure1-13).

Chemical Stability. This is resistance toreaction with alkali materials in portland ce-ments. Several rock types contain impureforms of silica that react with alkalies in ce-ment to form a gel. The gel absorbs water and

expands to crack or disintegrate the hardenedconcrete. This potential alkali-aggregatereaction may be estimated in the field only byidentifying the rock and comparing it toknown reactive types or by investigatingstructures in which the aggregate has pre-viously been used.

Surface Character. This refers to the bond-ing characteristics of the broken rock surface.Excessively smooth, slick, nonabsorbent ag-gregate surfaces bond poorly with cementingmaterials and shift readily under loads. Ex-cessively rough, jagged, or absorbent surfacesare likewise undisturbed because they resistcompaction or placement and require exces-sive amounts of cementing material.

Density. This is weight per unit volume. Inthe field, this may be estimated by “hefting” arock sample (see Table 1-7). Density reflectson excavation and hauling costs and may in-fluence the selection of rocks for specialrequirements (such as riprap, jetty stone, orlightweight aggregate). Among rocks of thesame type, density is often a good indicator ofthe toughness and durability to be expected,Table 1-8, page 1-24, lists the general ratingsof rock properties for each of the 18 typicalmilitary construction aggregates. These

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ratings serve only as a guide; each individualrock body must be sampled and evaluatedseparately. Table 1-9, page 1-24, providesgeneral guidance to determine the suitabilityof an unidentified rock sample for generalmilitary construction missions based on theevaluation of its physical properties.

Table 1-10, page 1-25, provides a rating forselected geologic materials concerning their

suitability as an aggregate for concrete or as-phalt or for their use as a base coursematerial. Rock materials that typically ex-hibit chemical instability in concrete aremarked with an asterisk. These materialsmay cause a concrete-alkali reaction due totheir high silica content. In general, felsites,chert, and obsidian should not be used as con-crete aggregate. The end result of thesereactions is the weakening, and in extremecases the failure, of the concrete design. Ap-parently, silica is drawn out of the aggregateto make a gel that creates weaknesses withinthe mix. The gel may expand with tempera-ture changes and prevent the proper bondingof the cement and aggregate.

Rock types with two asterisks may not bondreadily to bituminous materials. They re-quire special antistripping agents to ensurethat they do not “strip,” or separate, from thepavement mix. Stripping severely reducespavement performance.

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CHAPTER 2

S t r u c t u r a l G e o l o g y

Structural geology describes the form, pat-tern, origin, and internal structure of rockand soil masses. Tectonics, a closely relatedfield, deals with structural features on alarger regional, continental, or global scale.Figure 2-1, page 2-2, shows the major plates ofthe earth’s crust. These plates continuallyundergo movement as shown by the arrows.Figure 2-2, page 2-3, is a more detailed repre-sentation of plate tectonic theory. Moltenmaterial rises to the earth’s surface atmidoceanic ridges, forcing the oceanic platesto diverge. These plates, in turn, collide withadjacent plates, which may or may not be ofsimilar density. If the two colliding plates areof approximately equal density, the plateswill crumple, forming mountain range alongthe convergent zone. If, on the other hand,one of the plates is more dense than the other,it will be subducted, or forced below, thelighter plate, creating an oceanic trench alongthe convergent zone. Active volcanism andseismic activity can be expected in the vicinityof plate boundaries. In addition, military en-gineers must also deal with geologic featuresthat exist on a smaller scale than that of platetectonics but which are directly related to thereformational processes resulting from theforce and movements of plate tectonics.

The determination of geologic structure isoften made by careful study of the stratig-raphy and sedimentation characteristics oflayered rocks. The primary structure ororiginal form and arrangement of rock bod-ies in the earth’s crust is often altered by

secondary structural features. These secon-dary features include folds, faults, joints, andschistosity. These features can be identifiedand m appeal in the field through site inves-tigation and from remote imagery.

Section I. Structural Featuresin Sedimentary Rocks

BEDDING PLANESStructural features are most readily recog-

nized in the sedimentary rocks. They arenormally deposited in more or less regularhorizontal layers that accumulate on top ofeach other in an orderly sequence. Individualdeposits within the sequence are separatedby planar contact surfaces called beddingplanes (see Figure 1-7, page 1-9). Beddingplanes are of great importance to military en-gineers. They are planes of structuralweakness in sedimentary rocks, and massesof rock can move along them causing rockslides. Since over 75 percent of the earth’ssurface is made up of sedimentary rocks,military engineers can expect to frequentlyencounter these rocks during construction.

Undisturbed sedimentary rocks may berelatively uniform, continuous, and predict-able across a site. These types of rocks offercertain advantages to military engineers incompleting horizontal and vertical construc-tion missions. They are relatively stable rockbodies that allow for ease of rock excavation,as they will normally support steep rock

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faces. Sedimentary rocks are frequentlyoriented at angles to the earth’s “horizontal”surface; therefore, movements in the earth’scrust may tilt, fold, or break sedimentarylayers. Structurally deformed rocks add com-plexity to the site geology and may adverselyaffect military construction projects by con-tributing to rock excavation and slopestability problems.

Vegetation and overlying soil conceal mostrock bodies and their structural features.Outcrops are the part of a rock formation ex-posed at the earth’s surface. Such exposures,or outcrops, commonly occur along hilltops,steep slopes, streams, and existing road cutswhere ground cover has been excavated oreroded away (see Figure 2-3). Expensivedelays and/or failures may result when

military engineers do not determine the sub-surface conditions before committingresources to construction projects. Therefore,where outcrops are scarce, deliberate excava-tions may be required to determine the typeand structure of subsurface materials. Todetermine the type of rock at an outcrop, theprocedures discussed in Chapter 1 must befollowed. To interpret the structure of thebedrock, the military engineer must measureand define the trend of the rock on the earth’ssurface.

FOLDSRock strata react to vertical and horizontal

forces by bending and crumpling. Folds areundulating expressions of these forces. Theyare the most common type of deformation.Folds are most noticeable in layered rocks but

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rarely occur on a scale small enough to be ob-served in a single exposure. Their size variesconsiderably. Some folds are miles across,while others may be less than an inch. Foldsare of significant importance to military en-gineers due to the change in attitude, orposition, of bedding planes within the rockbodies (see Figure 2-4). These can lead to rockexcavation problems and slope instability.Folds are common in sedimentary rocks inmountainous areas where their occurrencemay be inferred from ridges of durable rockstrata that are tilted at opposite angles innearby rock outcrops. They may also berecognized by topographic and geologic mappatterns and from aerial photographs. Thepresence of tilted rock layers within a regionis usually evidence of folding.

TypesThere are several basic types of folds. They

are—Homocline.Monocline.Anticline.Syncline.Plunging.Dome.Basin.

A rock body that dips uniformly in one direc-tion (at least locally) is called a homocline (seeFigure 2-5a). A rock body that exhibits localsteplike slopes in otherwise flat or gently in-clined rock layers is called a monocline (seeFigure 2-5b). Monoclines are common inplateau areas where beds may locally assume

dips up to 90 degrees. The elevation of thebeds on opposite sides of the fold may differ byhundreds or thousands of feet. Anticlines areupfolds, and synclines are downfolds (see Fig-ure 2-5c and d, respectively). They are themost common of all fold types and are typi-cally found together in a series of fold undula-tions. Differential weathering of the rockscomposing synclines and anticlines tends toproduce linear valleys and ridges. Folds thatdip back into the ground at one or both endsare said to be plunging (see Figure 2-6).Plunging anticline and plunging synclinefolds are common. Upfolds that plunge in alldirections are called domes. Folds that arebowed toward their centers are calledbasins. Domes and basins normally exhibitroughly circular outcrop patterns on geologicmaps.

SymmetryFolds are further classified by their sym-

metry. Examples are-Asymmetrical (inclined).Symmetrical (vertical).Overturned (greatly inclined).Recumbent (horizontal).

The axial plane of a fold is the plane thatbisects the fold as symmetrically as possible.The sides of the fold as divided by the axialplane are called the limbs. In some folds, theplane is vertical or near vertical, and the foldis said to be symmetrical. In others, the axialplane is inclined, indicating an asym-metrical fold. If the axial plane is greatly

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inclined so that the opposite limbs dip in thesame direction, the fold is overturned. Arecumbent fold has an axial plane that hasbeen inclined to the point that it is horizontal.Figure 2-7 shows the components of an ideal-ized fold. An axial line or fold axis is theintersection of the axial plane and a par-ticular bed. The crest of a fold is the axis linealong the highest point on an anticline. Thetrough denotes the line along the lowest part ofthe fold. It is a term associated with synclines.

CLEAVAGE AND SCHISTOSITYFoliation is the general term describing the

tendency of rocks to break along parallel sur-faces. Cleavage and schistosity are foliationterms applied to metamorphic rocks.Metamorphic rocks have been altered by heatand/or pressure due to mountain building orother crustal movements. They may have apronounced cleavage, such as the metamor-phic rock slate that was at one time thesedimentary rock shale. Certain igneousrocks may be deformed into schists or igneis-ses with alignment of minerals to produceschistosity or gneissic foliation. The attitudesof planes of cleavages and schistosity can be

mapped to help determine the structure of arock mass. Their attitudes can complicaterock excavation and, if unfavorable, lead toslope stability problems.

FAULTSFaults are fractures along which there is

displacement of the rock parallel to the frac-ture plane; once-continuous rock bodies havebeen displaced by movement in the earth’scrust (see Figure 2-8). The magnitude of thedisplacement may be inches, feet, or evenmiles along the fault plane. Overall fault dis-placement often occurs along a series of smallfaults. A zone of crushed and broken rockmay be produced as the walls are draggedpast each other. This zone is called a “faultzone” (see Figure 2-9). It often containscrushed and altered rock, or “gouge,” and an-gular fragments of broken rock called“breccia.” Fault zones may consist ofmaterials that have been altered (reduced instrength) by both fault movement and ac-celerated weathering by water introducedalong the fault surface. Alteration of faultgouge to clay lowers the resistance of thefaulted rock mass to sliding. Recognition of

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faults is extremely important to military en-gineers, as they represent potential weaknessin the rock mass. Faults that cut very youngsediments may be active and create seismic(earthquake) damage.

RecognitionFaults are commonly recognized on rock

outcrop surfaces by the relative displacementof strata on opposite sides of the fault planeand the presence of gouge or breccia. Slicken-sides, which are polished and striatedsurfaces that result from movement along thefault plane, may develop on the broken rockfaces in a direction parallel to the direction ofmovement. Faulting may cause a discon-tinuity of structure that maybe observed atrock outcrops where one rock layer suddenlyends against a completely different layer.This is often observed in road cuts, cliff faces,and stream beds. Although discontinuity of

rock beds often indicates faulting, it may alsobe caused by igneous intrusions and uncon-formities in deposition. Faults that are notvisibly identifiable can be inferred by suddenchanges in the characteristics of rock strata inan outcrop or borehole, by missing or repeatedstrata in a stratigraphic sequence, or (on alarger scale) by the presence of long straightmountain fronts thrust up along the fault.Rock strata may show evidence of draggingalong the fault. Drag is the folding of rockbeds adjacent to the fault (see Figure 2-8 andFigure 2-10, page 2-8). Faults are identifiableon aerial photographs by long linear traces(lineations) on the ground surface and by theoffset of linear features such as strata,streams, fences, and roads. Straight faulttraces often indicate near-vertical faultplanes since traces are not distorted bytopographic contours.

TerminologyThe strike and dip of a fault plane is

measured in the same manner as it is for alayer of rock. (This procedure will bedescribed later.) The fault plane intersectionwith the surface is called the fault line. Thefault line is drawn on geologic maps. Theblock above the fault plane is called the hang-ing wall; the block below the fault plane iscalled the footwall. In the case of a verticalfault, there would be neither a hanging wallnor a footwall. The vertical displacementalong a fault is called the throw. The horizon-tal displacement is the heave. The slope onthe surface produced by movement along afault is called the fault scarp. It may vary in

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height from a few feet to thousands of feet ormay be eroded away (see Figure 2-11).

TypesFaults are classified by the relative direc-

tion of movement of the rock on opposite sidesof the fault. The major type of movementdetermines their name. These types are–

Normal (gravity).Reverse (thrust).Strike-slip.

Normal faults are faults along which thehanging wall has been displaced downwardrelative to the footwall (see Figure 2-12a).They are common where the earth’s surface isunder tensional stress so that the rock bodiesare pulled apart. Normal faults are also calledgravity faults and usually are characterized byhigh-angle (near-vertical) fault planes. In a

reverse fault, the hanging wall has been dis-placed upward relative to the footwall (seeFigure 2-12b). Reverse faults are frequentlyassociated with compressional forces thataccompany folding. Low-angle (near-horizon-tal) reverse faults are called overthrustfaults. Thrust faulting is common in manymountainous regions, and overthrusting rocksheets may be displaced many kilometersover the underlying rocks (see Figure 2-10).Strike-slip faults are characterized by oneblock being displaced laterally with respect tothe other; there is little or no vertical displace-ment (see Figure 2-12c). Many faults exhibitboth vertical and lateral displacement. Somefaults show rotational movement, with oneblock rotated in the fault plane relative to theopposite block. A block that is downthrownbetween two faults to form a depression iscalled a “graben” (see Figure 2-13a). Anupthrown block between two faultsproduces a “horst” (see Figure 2-13b). Horstsand grabens are common in the Basin andRange Province located in the western con-tinental United States. The grabens comprisethe valleys or basins between horst moun-tains.

JOINTSRock masses that fracture in such a way

that there is little or no displacement parallelto the fractured surface are said to be jointed,and the fractures are called joints (see Figure2-14, page 2-10). Joints influence the way therock mass behaves when subjected to the

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stresses of construction. Joints charac-teristically form planar surfaces. They mayhave any attitude; some are vertical, othersare horizontal, and many are inclined atvarious angles. Strike and dip are used tomeasure the attitude of joints. Some jointsmay occur as curved surfaces. Joints varygreatly in magnitude, from a few feet tothousands of feet long. They commonly occurin more or less parallel fractures called jointsets. Joint systems are two or more relatedjoint sets or any group of joints with a charac-teristic pattern, such as a radiating orconcentric pattern.

FormationJoints in rock masses may result from a

number of processes, including deformation,expansion, and contraction. In sedimentaryrocks, deformation during lithification or

folding may cause the formation of joints.Igneous rocks may contain joints formed aslava cooled and contracted. In dense, ex-trusive igneous rocks, like basalt, a form ofprismatic fracturing known as columnarjointing often develops as the rock cools rapidlyand shrinks. Jointing may also occur whenoverlying rock is removed by erosion, causinga rock mass to expand. This is known as ex-foliation. The outer layers of the rock peel,similar to the way that an onion does.

SignificanceBecause of their almost universal presence,

joints are of considerable engineering impor-tance, especially in excavation operations. Itis desirable for joints to be spaced closeenough to minimize secondary plugging andblasting requirements without impairing thestability of excavation slopes or increasing

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the overbreakage in tunnels. The spacing ofthe joints can control the size of the materialremoved and can also affect drilling andblasting. The ideal condition is seldom en-countered. In quarry operations, jointing canlead to several problems. Joints oriented ap-proximately at right angles to the workingface present the most unfavorable condition.Joints oriented approximately parallel to theworking face greatly facilitate blasting opera-tions and ensure a fairly even and smoothbreak, parallel to the face (see Figure 2-14).Joints offer channels for groundwater circula-tion. In excavations below the groundwatertable, they may greatly increase waterproblems. They also may exert an importantinfluence on weathering.

STRIKE AND DIPThe orientation of planar features is deter-

mined by the attitude of the rock. Theattitude is described in terms of the strike anddip of the planar feature. The most common

planar feature encountered is a sedimentarybed. Strike is defined as the trend of the lineof intersection formed between a horizontalplane and the bedding plane being measured(see Figure 2-15). The strike line direction isgiven as a compass bearing that is always inreference to true north. Typical strikes wouldthereby fall between north 0 to 90 degreeseast or north 0 to 90 degrees west. They arenever expressed as being to the southeast orsouthwest. Azimuths may be readily con-verted to bearings (for example, an azimuth of350 degrees would be converted to a bearingof north 10 degrees west).

The dip is the inclination of the beddingplane. It is the acute angle between the bed-ding plane and a horizontal plane (see Figure2-16). It is a vertical angle measured at rightangles from the strike line. The dip directionis defined as the quadrant of the compass thebed is dipping into (northeast, northwest,southeast, or southwest). By convention, thedip angle is given in degrees followed by the

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dip direction quadrant (for example, 30degrees northeast).

The strike and dip measurements aretaken in the field on rock outcrops with astandard Brunton compass. The Bruntoncompass is graduated in degrees and has abull’s-eye level for determining the horizontalplane when measuring the strike direction.The strike is determined by aligning the com-pass along the strike direction and readingthe value directly from the compass. In-cluded with the Brunton compass is aclinometer to measure the dip angle. Thisangle is measured by placing the edge of thecompass on the dipping surface at rightangles to the strike direction and reading theacute angle indicated by the clinometer (seeFigure 2-17, page 2-12).

Strike and dip symbols are used on geologicmaps and overlays to convey structural orien-tation. Basic symbols include those forinclined, vertical, and horizontal beds (seeFigure 2-18, page 2-12). For inclined beds,the direction of strike is designated as a longline that is oriented in reference to the mapgrid lines in exactly the same compass direc-tion as it was measured. The direction of thedip is represented by a short line that is al-ways drawn perpendicular to the strike lineand in the direction of the dip. The angle ofthe dip is written next to the symbol (see Fig-ure 2-18a, page 2-12). For vertical beds, the

direction of the strike is designated as it is forinclined beds. The direction of the dip is ashort line crossing the strike line at a rightangle extending on both sides of the strikeline (see Figure 2-18b, page 2-12). Forhorizontal beds, the direction of strike is rep-resented by crossed lines which indicate thatthe rock strikes in every direction. The dip isrepresented by a circle encompassing thecrossed lines. The circle implies that there isno dip direction and the dip angle is zero (seeFigure 2-18c, page 2-12). These basic symbolsare commonly used to convey attitudes ofsedimentary rocks (see Figure 2-19, page2-13). Similar symbols are used to convey at-titudes of other types of planar features, suchas folds, faults, foliation, and jointing in otherrock bodies.

Section II. Geologic Maps

TYPESGeologic maps show the distribution of

geologic features and materials at the earth’ssurface. Most are prepared over topographicbase maps using aerial photography and fieldsurvey data. From a knowledge of geologicprocesses, the user of a geologic map can drawmany inferences as to the geologic relation-ships beneath the surface and also much ofthe geologic history of an area. In engineer-ing practice, geologic maps are importantguides to the location of construction

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materials and the evaluation of foundation,excavation, and ground water conditions.

The following geologic maps are used formilitary planning and operations:

Bedrock or aerial maps.Surficial maps.Special purpose maps.

Bedrock or Aerial MapsThese maps show the distribution of rock

units as they would appear at the earth’s sur-face if all unconsolidated materials wereremoved. Symbols on such maps usuallyshow the age of the rock unit as well as majorstructural details, such as faults, fold axes,and the attitudes of planar rock units or fea-tures. Thick deposits of alluvium (materialdeposited by running water) may also beshown.

Surficial MapsThese maps show the distribution of uncon-

solidated surface materials and exposedbedrock. Surface materials are usually dif-ferentiated according to their physical and/orchemical characteristics. To increase theirusefulness as an engineering tool, most surfi-cial maps show the distribution of materials

at some shallow mapping depth (often onemeter) so that minor residual soils anddeposits do not mask the essential features ofengineering concern.

Special Purpose MapsThese maps show selected aspects of the

geology of a region to more effectively presentinformation of special geologic, military, orengineering interest. Special purpose maps areoften prepared to show the distribution of—

Engineering hazards.Construction materials.Foundation conditions.Excavation conditions.Groundwater conditions.Trafficability conditions.Agricultural soils.Surface-water conditions.

Very detailed, large-scale geologic mapsmay show individual rock bodies, but thesmallest unit normally mapped is the forma-tion. A formation is a reasonably extensive,distinctive series of rocks deposited during aparticular portion of geologic time (see Table2-1, page 2-15). A formation may consist of asingle rock type or a continuous series ofrelated rocks. Generally, formations are

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named after the locality where they were firstdefined. Formations may be grouped by age,structure, or lithology for mapping purposes.

SYMBOLSSymbols are used to identify various fea-

tures on a geologic map. Some of thosefeatures are—

Formations (see Figure 2-21, page 2-18).Contacts (see Figure 2-21, page 2-18).Attitudes (see Figure 2-21, page 2-18).Fault lines and fold axes (see Figure2-21, page 2-18).Cross sections (see Figure 2-23, page2-19).

FormationsLetters, colors, or symbolic patterns are

used to distinguish formations or rock unitson a geologic map. These designators shouldbe defined in a legend on the map. Letter sym-bols usually consist of a capital letterindicating the period of deposition of the for-mation with subsequent letters (usuallylower case) that stand for the formal name ofthe unit, (see Table 2-1). Maps prepared by theUS Geological Survey and many other agen-cies use tints of yellow and orange forCenozoic rocks, tints of green for Mesozoicrocks, tints of blue and purple for Paleozoicrocks, and tints of red for Precambrian rocks,Symbolic patterns for various rock types aregiven in Figure 2-20, page 2-17.

ContactsA thin, solid line shows contacts or boun-

daries between rock units if the boundariesare accurately located. A dashed line is usedfor an approximate location and a dotted lineif the cointact, is covered or concealed. Ques-tionable or gradational contacts are shown bya dashed or dotted line with question marks.

AttitudesStrike and dip symbols describe planes of

stratification, faulting, and jointing. Thesesymbols consist of a strike line long enough sothat its bearing can be determined from themap, a dip mark to indicate the dip directionof the plane being represented, and a number

to show the value (in degrees) of the dipangle. The number is omitted on repre-sentations of both horizontal and verticalbeds, because the values of the dips are auto-matically acknowledged to be 0 and 90 de-grees, respectively. Figure 2-22, page 2-19,shows the placement of strike and dip sym-bols on a geologic map with respect to the loca-tion and orientation of a sedimentary rockbed.

Fault Lines and Fold AxesHeavy black lines, which may be solid,

dashed, or dotted (as described for contacts),show fault lines and fold axes. The direc-tion of movement along faults is shown byarrows or by the use of symbols to indicateup thrown and down thrown sides. Thearrows accompanying fold axes indicatethe dip direction of the limbs and/or theplunge direction of the fold.

Cross SectionsCross sections show the distribution of

geologic features and materials in a verticalplane along a line on a map. Cross sectionsare prepared in much the same way astopographic profiles using map, field, andborehole data. Geologic sections accompanymany geologic maps to clarify subsurfacerelationships, Like geologic maps, geologicsections are often highly interpretive, espe-cially where data is limited and structuresare complex or concealed by overburden.Maps and sections use similar symbols andconventions. Because of the wealth of datathat can be shown, geologic maps and sectionsare the two most important means of record-ing and communicating geologic information.

OUTCROP PATTERNSAn outcrop is that part of a rock formation

that is exposed at the earth’s surface. Out-crops are located where there is no existingsoil cover or where the soil has been removed,leaving the rock beneath it exposed. Outcropsmay indicate both the type and the structureof the local bedrock. Major types of structuralfeatures can be easily recognized on geologicmaps because of the distinctive patterns theyproduce. Figures 2-24 through 2-31, pages2-20 through 2-21, show basic examples ofcommon structural patterns.

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Each illustration contains a block diagram illustrations include some of the followingstructural features:

Horizontal strata.Inclined strata.Domes.Basins.Plunging folds.Faults.Intrusive rocks.Surficial deposits.

showing a particular structural feature alongwith its topographic expression. The outcroppattern of each rock unit shown on the blockdiagram is projected to a horizontal plane,resulting in the production of a geologic mapthat is also shown. This allows the reader toreadily relate the structure shown on theblock diagram to the map pattern. Structuraldetails can be added to basic maps usingthe symbols in Figure 2-21, page 2-18. The

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Horizontal StrataDendritic (branching or treelike) drainage

patterns typically develop on horizontalstrata and cut canyons or valleys in whichprogressively older rock units are exposed atdepth (see Figure 2-24, page 2-20). The resultis that the map patterns of horizontal strataparallel stream valleys, producing dendriticpattern on the geologic map. Although allmaps do not show topographic contour lines,the contacts of horizontal rock units parallel

the contours. Escarpments and gentle slopesgenerally develop on resistant and nonresis-tant beds, respectively, producing variationsin the width of the map outcrop pattern. Theupper and lower contacts are close togetheron steep cliffs; on gentle slopes of the sameformation, the contacts are further apart.The map width of the outcrops of horizontalbeds does not indicate the thickness of thestrata. Gently dipping beds develop the samebasic outcrop pattern as horizontal beds.

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Structural Geology 2-20

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However, the contacts of gently dippingstrata, if traced far enough up a valley, crosstopographic contours and form a large V-shaped pattern that points in the directionthe beds dip, assuming that the beds do not,dip in the direction of the stream gradient,but at a smaller angle.

Inclined StrataWhen a sequence of rocks is tilted and cut

off by erosion, the outcrop pattern ap-pears as bands that, on a regional basis, areroughly parallel. Where dipping strata crossa valley, they produce a V-shaped outcroppattern that points in the direction of dip, ex-cept in cases where the beds dip in thedirection of the stream gradient at smallerangles than the gradient. The size of the V isinversely proportional to the degree of dip.

Low-angle dip (large V) (see frontpart of Figure 2-25, page 2-20).High-angle dip (small V).Vertical dip (no V) (see back part ofFigure 2-25, page 2-20).

Other relationships that are basic to the in-terpretation of geologic maps are also shownin Figure 2-25, page 2-20. For example, theyshow that older beds dip toward youngerbeds unless the sequence has been over-turned (as by folding or faulting). Maps alsoshow that outcrop width depends on thethickness of the beds, the dip of the beds (lowdip, maximum width), and the slope of thetopography (steep slope, minimum width).

DomesEroded dome-shaped structures form a

roughly circular outcrop pattern with bedsdipping away from a central area in which theoldest rocks outcrop (see Figure 2-26, page2-20). These structures range from small fea-tures only a few meters across to greatUpwarps covering areas of hundreds orthousands of square kilometers.

Drainage patterns are helpful in interpret-ing a domal structure. Radial drainagepatterns tend to form on domes. Streams cut-ting across the resistant beds permit one to

apply the “rule of Vs” as explained above tointerpret the direction of dip.

BasinsEroded structural basins form an outcrop

pattern very similar to that of an eroded dome(see Figure 2-27, page 2-20). However, twomajor features serve to distinguish them:younger rocks outcrop in the center of a basinand, if the structure has been dissected bystream erosion, the outcrop Vs normally pointtoward the center of a basin, whereas theyusually point away from the center of a dome.

Plunging FoldsFolding is found in complex mountain

ranges and sometimes in lowlands andplateaus. When folds erode, the oldest rocksoutcrop in the center of the anticlines (or up-folds) and the youngest rocks outcrop in thecenter of the synclines (or downfolds). Theaxes of folded beds are horizontal in somefolds, but they are usually inclined. In thiscase, the fold is said to plunge. Plunging foldsform a characteristic zigzag outcrop patternwhen eroded (see Figure 2-28, page 2-21). Aplunging anticline forms a V-shaped patternwith the apex (or nose) of the V pointing in thedirection of the plunge. Plunging synclinesform a similar pattern, but the limbs of thefold open in the direction of the plunge.

FaultsFault patterns on geologic maps are distinc-

tive in that they abruptly offset structuresand terminate contacts (see Figure 2-29,page 2-21). They are expressed on the geologicmap by heavy lines in order to be readilydistinguished. Some common types are–

Normal.Reverse.Thrust.

Normal and Reverse (see A and B, respec-tively, in Figure 2-29, page 2-21). Both normaland reverse fault planes generally dip at ahigh angle, so outcrop patterns are relativelystraight. Older rocks are usually exposed onthe upthrown block. It is thus possible todetermine the relative movement on most

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high-angle faults from map relationsalone. Linear streams, offsets, linear scarps,straight valleys, linear-trending springs orponds, and omitted or repeated strata arecommon indications of faulting (see para-graph on recognition of faults, page 2-7).

Thrust (see C in Figure 2-29, page 2-21).Thrust faults are reverse faults that dip atlow angles (less than 15 degrees) and havestrati graphic displacements, commonlymeasured in kilometers (see Figure 2-10, page2-8). The trace of the thrust commonly formsVs where it intersects the valleys. The Vspoint in the direction of the fault plane dip,except in cases where the fault plane dips inthe direction of the stream gradient, but asmaller angle. Erosion may form windows(fensters) through the thrust sheet so that un-derlying rocks are exposed or produceisolation remnants (klippen) above the un-derlying rocks. Hachure symbols are used todesignate the overthrust block that usuallycontains the oldest rocks.

IntrusionsLarger igneous intrusions, such as

batholiths and stocks, are typically discor-dant and appear on geologic maps as ellipticalor roughly circular areas that cut across thecontacts of surrounding formations (see Fig-ure 2-30, page 2-21). Smaller discordantintrusions, such as dikes, are usually tabularand appear on geologic maps as straight,usually short, bands. However, some dikesare lenticular and appear as such on the map.Concordant intrusions, such as sills and lac-coliths, have contacts that parallel those ofthe surrounding formations (see Figure 1-5,page 1-7).

The relative age of igneous bodies can berecognized from crosscutting relationships.The younger intrusions cut the older ones.With this in mind, it is clear from the relation-ships in Figure 2-30, page 2-21, that theelliptical stock is the oldest intrusion, thenortheast trending dike the next oldest, andthe northwest trending dike the youngest.The age of the small discontinuous dikes nearthe western part of the map is younger than

that of the stock, but the age relation withthe other dikes is not indicated.

Surficial DepositsSurficial deposits are recent accumulations

of various types of sediment or volcanic debrison the surface of the landscape (see Figure2-31, page 2-21). The primary types are—

Windblown sand and loess.Stream channel and floodplain deposits.Landslide deposits.Glacial deposits.Present beaches and other shorelinesediments.

Section III. EngineeringConsiderations

ROCK DISTRIBUTIONGeologic structure controls the distribution

of rock bodies and features along and beneaththe earth’s surface. The presence and orienta-tion of such features as bedding, folding,faulting, and unconformities must be deter-mined before construction begins. Otherwise,foundation, excavation, and groundwater con-ditions cannot be properly evaluated.

ROCK FRAGMENTATIONRocks tend to fracture along existing zones

of weakness. The presence and spacing ofbedding, foliation, and joint planes can con-trol the size and shape of rock fragmentsproduced in quarries and other excavations.Operational and production costs may beprohibitive if rock fragments are too large, toosmall, too slabby, or too irregular for ag-gregate requirements. Advantageous joint orbedding spacings can significantly reduce ex-cavation and aggregate production costs.

Many weak, thinly bedded, or highly frac-tured rocks can be excavated without blastingby using ripping devices drawn by heavycrawler tractors. When ripping is used tobreak up and loosen rock for removal, thework should proceed in the direction of thedip. This prevents the ripping devices fromriding up the dip surfaces and out of the rockmass (see Figure 2-32, page 2-24).

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Most rock must be drilled and blasted forremoval. Where joints or bedding planes in-cline across the axis of the drill hole, drill bitstend to follow these planes, causing the holesto be misaligned; or, more often, the bits tobind, stick, or break off in the holes (seeFigure 2-33). Open fractures and layers ofweak rock greatly reduce blasting effective-ness by allowing the force of the blast toescape before the surrounding rock has beenproperly fragmented. Such situations re-quire special drilling and blastingtechniques that generally lower the ef-ficiency of quarrying operations.

ROCK SLIDES AND SLUMPSMassive rock slides may occur where un-

confined rock masses overlie inclinedbedding, foliation, fault, or joint surfaces (seeFigure 2-34). The risk of such slides isgenerally greatest over smooth, continuous,water- or clay-lubricated surfaces that dipsteeply toward natural or man-made excava-tions. The following general observationsmay assist in evaluating hazards (see Figure2-35):

Most rocks are stable above surfacesthat dip less than about 18 degreestoward an excavation. Excavation slopeswith horizontal to vertical ratios of 1:2

Structural Geology 2-24

(1 foot horizontal to 2 feet vertical)are usually feasible in such cases un-less weak rocks underlie the excava-tion sidewalls.Some rocks may slide on surfaces thatdip between about 18 degrees and 35 de-grees toward an excavation, particularlyif the surfaces are wet, clayey,smooth, and continuous. Side slopesof 1:1 or flatter may be required tostabilize such surfaces. It may benecessary to remove the hazardousrock entirely. Where excessive ex-cavations must be avoided for economic,environmental, or other reasons, ar-tificial supports or drainage worksmay be employed to stabilize therock.Unless rock surfaces are discon-tinuous or very rough and uneven,

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most unconfined rocks will slide oversurfaces steeper than about 35degrees. Excavation side slopesshould be cut back to the dipping sur-face or slightly beyond to assurestability against sliding.Rocks along planes of weakness thatdip almost vertically toward or awayfrom excavation sidewalls should becut on horizontal to vertical ratios of1:4 or 1:2 to prevent toppling failures.This is particularly important if the

rocks are weak or the planes of weak-ness are closely spaced.

WEAK ROCKSWeak rocks, such as shales, may shear or

crush under the weight of overlying rock andallow excavation sidewalls to slump or cavein. Such failures can be prevented by instal-ling artificial supports or by using flattenedor terraced side slopes to reduce the load onthe potential failure zone.

FAULT ZONESFault zones are often filled with crushed

and broken rock material. When thesematerials are water-soaked, they mayweaken and cause the fault zone to becomeunstable. Such zones are extremely hazard-ous when encountered in tunneling and deepexcavations because they frequently slump orcave in. Artificial supports are usually re-quired to stabilize such materials.

GROUNDWATERWater entering the ground percolates

downward, through open fractures and per-meable rocks, until it reaches a subsurfacezone below which all void spaces are filled

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with water. Where such ground water is in-tersected in an excavation, such as a road cutor tunnel, drainage problems may occur; rockslides triggered by the weakening and/orlubricating of the rock mass may result. Inaddition, water trapped under hydrostaticpressure in fault zones, joints, and permeablerock bodies can cause sudden floodingproblems when released during excavation.Permeable rock zones may also permit waterto escape from canals and reservoirs. How-ever, if properly evaluated, the structuralconditions that produce ground waterproblems can also provide potential suppliesof groundwater or subsurface drainage for en-gineering projects.

ROAD CUT ALIGNMENTThe most advantageous alignment for road

cuts is generally at right angles (perpen-dicular) to the strike of the major planes ofweakness in the rock (usually the bedding).This allows the rock surfaces to dip along thecut rather than into it (see Figure 2-36a and2-36 b). Where roads must be aligned parallelto the strike of the major planes of weakness,the most stable alignment is one in which themajor planes of weakness dip away from theexcavation; however, some overhang shouldbe expected (see Figure 2-36c).

QUARRY FACESQuarries should normally be developed in

the direction of strike so that the quarry faceitself is perpendicular to strike (see Figure2-37a, page 2-28). This particular orientationis especially important where rocks are steeplyinclined, because it allows for the optimiza-tion of drilling and blasting efforts by creatinga vertical or near-vertical rock face after eachblast. If necessary, quarries maybe workedperpendicular to the strike direction in in-stances where the rocks are not steeplyinclined, but drilling and blasting will proveto be more difficult. In addition, if the rocksdip away from the excavation, overhang andoversized rocks can be expected (See Figure 2-37b, page 2-28). If the rocks dip toward theexcavation, problems with slope instabilityand toeing may result (See Figure 2-37c, page2-28). In massive igneous rock bodies and

Structural Geology 2-26

horizontal sedimentary rock layers, the direc-tion of quarrying should be chosen based onthe most prominent joint set or other discon-tinuity.

ROCK DEFORMATIONRocks may behave as elastic, plastic, or vis-

cous solids under stress. Heavy loads, such asdams, massive fills, tall buildings, or bridgepiers, may cause underlying rocks to com-press, shear, or squeeze laterally. Particularproblems exist where rocks of differentstrength underlie a site. For example, whereweak shale and stronger limestone supportdifferent parts of the same structure, thestructure may tile or crack due to uneven set-tlement.

The removal of confining stresses duringexcavation may cause rocks to expand orsqueeze into the excavated area. Suchproblems seldom cause more than an increasein excavation or maintenance costs for roads,airfields, and railroads; however, they maycause serious damage to dams, buildings,canals, and tunnels where deformation can-not be tolerated. Weak clays and shales(especially compaction shales) are the mostcommon cause of such problems. Other rockscan also cause trouble if they are weatheredor if they have been under great stress. Toneutralize the effects of rock flow or rebound,the following may be required:

Additional excavation.Artificial supports or hold-downs.Compensating loads.Adjustment periods before construc-tion.

EARTHQUAKES (FAULT MOVEMENTS)Movement along active faults produces

powerful ground vibrations and rock dis-placements that can seriously disruptengineering works. Unless proven otherwiseby geological or historical evidence, all faultsthat disrupt recent geologic deposits shouldbe considered active. Many areas sufferearthquakes as a result of deep-seated faultsthat do not appear at the earth’s surface.Consequently, seismic hazards must bethoroughly investigated before any major

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structure is undertaken. Power lines, dams, vertical structures must be designed to ac-canals, tunnels, bridges, and pipelines across commodate the lateral movements andactive faults must be designed to accom- vibrations associated with earthquakesmodate earth movements without failure, where seismic hazards exist. Expect in-Buildings and airfields should be located creased seismic risk in marginal areas ofaway from known active fault zones. All continental plates (see Figure 2-1, page 2-2).

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Structural Geology 2-29

DAMS

Dam sites are selected on the basis oftopography, followed by a thorough geo-logic investigation. A geologic investiga-tion should include, as a minimum—

• Soundness. Determine the sound-ness of underlying foundation bedsand their ability to carry the desig-nated load.

• Water integrity. Determine the de-gree of watertightness of the foun-dation beds at the dam location andthe necessary measures, if any, tomake the underlying geologic stratawatertight.

• Duration of water exposure. Studythe effect that prolonged exposure towater has on the foundation bed-rock.

• Potential for quake activity. De-termine the possibility of earthmovement occurring at the dam siteand what it takes to safeguardagainst such failures.

• Availability of materials. Investi-gate what natural materials areavailable near the site (potentialquarries, sand, gravel, fill).

Generally, igneous rocks make themost satisfactory material for a damfoundation. Most igneous rocks are asstrong as or stronger than concrete. How-ever, many tuffs and agglomerates areweak. Solution cavities do not occur in ig-neous rocks because they are relativelyinsoluble; however, leakage will takeplace along joints, shear zones, faults, andother fissures. These can usually besealed with cement grout.

Most metamorphic rocks have founda-tion characteristics similar to igneousrocks. Many schists are soft, so they areunsuitable as foundations for large, con-crete dams. Marble is soluble and some-times contains large solution cavities. As

a rule, metamorphic rocks can be treatedwith cement grout.

Sandstones allow seepage throughpores, joints, and other fissures. The highporosity and low permeability of manysandstones make them difficult to treatwith cement grout. Limestone’s solubilitycreates large underground cavities. Gen-erally, the strength of shale compares fa-vorably with that of concrete; however, itselasticity is greater. Shale is normally wa-tertight.

TUNNELS

After determining the general locationand basic dimensions of a tunnel, considergeological problems before designing andconstructing it. Civil engineers dealingwith tunnel construction understand theneed for geological data in this field, sofailure due to the lack of geological infor-mation seldom occurs. However, manyfailures do occur because engineers im-properly interpret the available geologicalfacts.

Folded Strata

Extensive fracturing often exists alongthe axis of folded rock. This presents diffi-culties in tunneling operations. In an an-ticline, such fractures diverge upward; ina syncline, they diverge downward. If atunnel is placed along the crest of a fold,the engineer can expect trouble fromshattered rock. In such a case, the tunnelmay have to be lined its entire length. Ina syncline, an engineer could face addi-tional trouble, even with moderate frac-turing. The blocks bounded by fractureplanes are like inverted keystones and arevery likely to drop. When constructingtunnels in areas of folded rocks, the engi-neer should carefully consider the geologicstructure. If a tunnel passes throughhorizontal beds, the engineer should en-counter the same type of rock throughoutthe entire operation. In folded strata,

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many series of rock types can be encoun-tered. Therefore, carefully mapping geo-logical structures in the construction areais important.

Faulted Strata

As with folded rocks, the importance ofhaving firm, solid rock cannot be stressedenough, not only for safety and conven-ience in working but also for tunnel main-tenance after completion. If rock is shat-tered by faulting, the tunnel must belined, at least in the crushed-rock area.Also, if the fault fissure extends to thesurface, it may serve as a channel forrainwater and groundwater.

Groundwater Problems

Groundwater presence is often themain trouble source in tunnel construc-tion. If tunnel grades cannot facilitategroundwater drainage, it may be neces-sary to pump throughout the tunnel.Therefore, it is necessary to have accurateinformation before beginning tunnel con-struction. Apply grout or cement, whenpossible, to solve water problems.

BRIDGES

Geological principles also apply inbridge construction. The weight of thebridge and the loads that it supports mustbe carried by the underlying foundationbed. In most cases, bridges are con-structed for convenience and economy, sothey must be located in specified areas.Therefore, engineers cannot alwayschoose the best site for piers and abut-ments. Once construction begins, thebridge location cannot be easily changedand should only be done so under excep-tional circumstances.

As a rule, bridges are constructed tocross over rivers and valleys. An older riv-erbed or other depression (caused by gla-ciation or river deposits) could be com-pletely hidden below the existing river-bed. Problems could arise if such a buried

valley is not discovered before bridge con-struction begins. For example, riverbedscontain many types of deposits, includinglarge boulders. If preliminary work is notcarefully done and correlated with geo-logical principles, existing boulder depos-its could be mistaken for solid bedrock.

BUILDINGS

Ground conditions at a building sitemay be one of three general types:

• On or near ground surface. Solidrock could exist at ground surface orso close to the surface that the foun-dation of the building can be placeddirectly on it.

• Below ground surface. Bedrock couldexist below ground surface so thatan economic, practical foundationcan be used to support the buildingload.

• Far below ground surface. Thenearest rock stratum could be so farbelow the surface that it cannot beused as a foundation bed. A build-ing’s foundation must be built onthe material that forms the surfacestratum.

If solid rock is present, its strength andphysical properties must be determined.When the foundation consists of loose, un-consolidated sedimentary material, propersteps must be taken to solve the problemof subsidence. Structures that are sup-ported on bedrock, directly or throughpiles or piers, will settle by extremelysmall amounts. If a foundation has beensupported in unconsolidated strata, ap-preciable settlement can be expected.

QUARRY OPERATIONS

Natural sand and gravel are not al-ways available, so it is sometimes neces-sary to produce aggregate by quarryingand processing rock. Quarrying is nor-mally done only where other materials of

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adequate quality and size cannot be ob-tained economically and efficiently.

Many rock types are suitable for con-struction, and they exist throughout theworld. Therefore, the quality and durabil-ity of the rock selected depend on localconditions. The following rock types areusually easy to quarry. They are also du-rable and resistant to weathering.

• Granite. As a dimension stone,granite is fairly durable and has atexture and a color that are desir-able for polishing. As a constructionmaterial for base courses and ag-gregate, it is not as desirable assome of the denser igneous rocks.

• Felsite and rhyolite. These are du-rable and make good aggregate forbase courses. They are not suitablefor concrete aggregate.

• Basalt. The dense, massive varietyof basalt is excellent for crushedrock, base course, and bituminousaggregate. It is very strong and du-rable. Due to basalt’s high compres-sive strength, processing it may bemore difficult than processing otherrocks.

• Sandstone. Few sedimentary rocksare desirable for construction due totheir variable physical properties,but sandstone is generally durable.However, deposits must be evalu-ated individually, due to the vari-able nature of grains and cementpresent in the rock.

• Limestone. Limestone is widely usedfor road surfacing, in concrete, andfor lime production. It is a good, all-around aggregate.

• Gneiss. Most varieties of gneisshave good strength and durabilityand make good road aggregate.

• Quartzite. Quartzite is hard and du-rable, so it is an excellent rock forconstruction. However, it can be dif-ficult to quarry.

• Marble. The texture and color ofmarble make it desirable for di-mension stone. It can also be usedfor base course and aggregate ma-terial.

Factors that enhance the easy removalof rock often diminish its suitability forconstruction. Strong, durable, unweath-ered rock usually serves best for em-bankment and fill, base and surfacecourse material, concrete aggregate, andriprap. However, these rocks are the mostdifficult to quarry or excavate.

Soils continuously change. Weathering,chemical alteration, dissolution, and pre-cipitation of components all occur as soilsaccumulate and adjust to their environ-ment. Particle coatings and natural ce-ments are added and removed. Solublecomponents wash downward (leach) oraccumulate in surface layers by evapora-tion. Plants take root and grow as soilprofiles develop. These changes tend tobecome more pronounced with increasingage of the soil deposit. These possible al-terations to the sediment may affect itsutility in construction. The soils of naturalgeological deposits are commonly used asconstruction materials.

Section IV. AppliedMilitary Geology

The science and applied art of geologyis an important component of militaryplanning and operations. Today, comput-ers, satellites, geographic information sys-tems, geographic positioning systems, andsimilar technology have catapulted theart and science of geology as an everydaytool for military commanders and engi-neers.

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MILITARYGEOGRAPHIC INTELLIGENCE

The purpose of geographic intelligenceis to obtain data about terrain and cli-mate. Commanders use the information tomake sound decisions and soldiers use itto execute their missions. In planning anoperation, commanders and their staffanalyze the effects that terrain and cli-matic conditions will have on the activi-ties of friendly and enemy forces. Knowl-edge of how geology controls and influ-ences terrain is helpful for classifying andanalyzing terrain and terrain effects.When provided with adequate geographicand geologic intelligence, commanders areable to exploit the advantages of the ter-rain and avoid or minimize its unfavor-able aspects. Data on soil movement, thepresence of hard rock, and the kind anddistribution of vegetation is needed whenconsidering concealment and cover, cross-country travel, and field fortifications.Strategic intelligence studies prepared byDepartment of Defense agencies providedetailed geographic and terrain informa-tion (Table 2-2) useful for compiling andanalyzing geographic intelligence.

Maps and Terrain Models

Maps are a basic source of terrain in-formation. Geologic maps show the distri-bution, age, and characteristics of geologicunits. They may also contain cross sec-tions that show the subsurface occurrenceof rock and soil. Maps may have text ex-plaining physical properties; engineeringproperties; and other information onnatural construction materials, rock for-mations, and groundwater resources. Soilmaps are commonly presented under anagricultural classification but may beused for engineering purposes after theyhave been converted to engineering no-menclature.

A terrain model is a three-dimensionalgraphic representation of an area showingthe conformation of the ground to scale.Computer-generated images have re-cently been developed that display two-dimensional form images in three-dimensional form for viewing from anyangle.

Remote Imagery

Aerial and ground photography andremote imagery furnish information thatis not readily available or immediatelyapparent by direct ground or aerial obser-vation. Examples are infrared photogra-phy and side-looking radar. Imagery per-manantly preserves information so that itis available for later study. Photographsnormally depict more recent terrain fea-tures than available maps.

Terrain Classification

Land forms are the physical expressionof the land surface. For terrain intelli-gence purposes, major land forms are ar-bitrarily described on the basis of localrelief (the difference in elevation betweenland forms in a given area).

GEOLOGY IN RESOLVINGMILITARY PROBLEMS

To apply geology in solving militaryproblems, personnel must first considergeologic techniques and uses and then de-termine how to acquire the needed infor-mation. Commanders can use geology inthree ways—geologic and topographicmap interpretation, photo interpretation,and ground reconnaissance.

Maps

Combination topographic and geologicmaps can tell commanders and engineerswhat the ground looks like. Map informa-tion should be made available early in op-eration planning. The success of many

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military operations depends on the speedof required advance construction. Speed,in turn, depends on completely under-standing the needs and adequately plan-ning to meet those needs in a particulararea. Topographic maps are important

sources of information on slope and landforms. One problem in using a topo-graphic map is that some relief or rough-ness may be hidden between the contourlines. Generally, the larger the intervalbetween contour lines and the smaller the

Table 2-2. Reports for geographic/terrain intelligence

Report Title Report ApplicationImagery interpretation Planning combat and support operations

Planning recon activitiesSupporting requests for terrain intelligenceAnalyzing areas of operationsPlanning terrain studies

Terrain study on soils Supporting communications planningExecuting movement, maneuver operationsPlanning combat operations (construction of landing strips, maintenance of

culverts)Selecting avenues of approach

Terrain study on rocks Planning movement, maneuver operationsPlanning combat operations (construction, maintenance, and destruction of

roads, bridges, culverts, and defensive installations)Selecting avenues of approach

Terrain study on waterresources

Selecting locations of and routes to water pointsPlanning combat operations (street crossing, bridging)Supporting logistics planning

Terrain study on drainage Supporting communications planningPlanning combat operations (constructing roads, fortifications, and fjords)Supporting river crossings and cross-country movement

Terrain study on surfaceconfiguration

Supporting communications planningPlanning observation posts and recon activityPlanning tactical operations and executing tactical objectivesPlanning barrier and denial operationsPlanning artillery support

Terrain study on the stateof the ground

Planning movement, maneuver operationsPlanning ADM activityPlanning combat operations (constructing, maintaining, and repairing roads,

fjords, landing strips, and fortifications)Planning logistics support

Terrain study on con-struction suitability

Planning combat operations (constructing fortifications, landing strips, cam-ouflage, obstacles, and a CP’s supply installations)

Selecting construction supply-point locationsTerrain study on coastsand landing beaches

Planning amphibious operations (preparing and removing obstacles and forti-fications)

Planning recon activityPlanning port construction

Terrain study on cross-country movement

Planning and executing maneuver, movement operationsPlanning logistics supportPlanning barrier and denial operationsPlanning engineer combat operations

Terrain study on airbornelanding areas

Planning area-clearing supportPlanning recon activityPlanning combat operations (constructing and repairing landing strips)Selecting helicopter landing zones

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scale of the map, the more the relief ishidden. Conversely, the smaller the con-tour intervals and the larger the scale ofthe map, the less the relief is hidden.

Photographic Interpretation

Many principles that make a geologicmap useful for estimating the terrainsituation also apply to the usefulness ofaerial photographs. The interpreter’s skillis very important. Without a professionalphoto interpretation and the knowledge ofgeologic process and forces, a great deal ofinformation may be overlooked. In prepar-ing terrain intelligence, aerial photo-graphs alone will not provide enough in-formation. Geologic maps must also beavailable. Aerial photographs are com-pletely reliable for preparing tactical ter-rain intelligence. However, the usefulnessof aerial photographs varies with thescale of the report being prepared.

Reconnaissance

Interpretation of the land for militarypurposes can be accomplished by studyingmaps and can be even more accurate byadding photographs. Using maps or pho-tographs is highly effective, but it cannotcompare in accuracy to actual ground ob-servation. In a tactical situation, such aswhen attacking a defended position, theknowledge of the terrain behind the posi-tion is vital for planning the next move.Terrain may be different on the side thatcannot be seen. Generally, the differenceis expressed in the geology of the slopethat can be observed. By combiningground observation and reconnaissanceby a trained observer (geologist) withaerial and map interpretation, the com-mander can plan ahead. Reconnaissanceof secure territory can be used to an evengreater advantage when developing thearea of occupation or advancement.

REMOTE IMAGERY

The major kinds of remotely sensedimagery are photography, radar, andmultispectral or digital scanner imagery.Since the 1930s, various worldwide agen-cies have acquired a large amount of re-mote imagery. The quality, scale, and na-ture of the coverage vary considerably be-cause new techniques and equipment arebeing developed rapidly. Remote imagerycan be—

• Generated quickly in a specifiedtime.

• Displayed accurately.

• Produced in a useful and storableformat.

• Produced in volume (Table 2-3).

High-altitude aircraft and spacecraftimagery are desirable for regional geologicmapping and delineating major structuralfeatures. Stereo coverage of low-, medium-,and high-altitude photography is used fordetailed geologic mapping of rock units,structure, soil type, groundwater sources,and geologic hazards such as slope failure,sinkholes, fracturing zones, and flooding.

FIELD DATA COLLECTION

Field data collection is necessary to—

• Supplement existing information ob-tained from published and unpub-lished literature.

• Obtain site-specific, detailed infor-mation that describes the local geol-ogy.

Mission constraints, such as time, re-sources, weather, and political climate,limit the amount of field investigationthat can be conducted. The followingmethods and procedures, which were de-signed primarily for civilian peacetime

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projects, serve as a guide for the kinds ofgeologic information that can be obtainedin field investigation.

All available geologic information(literature, geologic and topographicmaps, remote sensing imagery, boringlogs, and seismic data relative to the gen-eral area of the project) should be col-lected, identified, and incorporated into

the preliminary study for the project.This preliminary study should be com-pleted before field investigations begin. Apreliminary study allows those assignedto the project to become familiar withsome of the engineering problems thatthey may encounter. Geologic informationavailable in published and unpublishedsources must be supplemented by data

Table 2-3. Sources of remote imagery

ProcurementPlatform

Imagery Format Scale Coverage Source Agency

Low-, medium-,and high-altitudeaircraft

Black and white orcolor stereo pairs ofaerial photos ofhigh resolution

1:12,0001:125,000

Limited worldwide(low altitude, 1942to present; highaltitude, 1965 topresent)

USGS, EROS datacenter, Sioux Falls,SD

Low-, medium-,and high-altitudeaircraft

Black and white,color, color IR,black and white IR,thermal IR, SLAR,multiband imagery(reproductions ofimagery are avail-able to all US mili-tary organizationsand US govern-ment agencies)

1:1,0001:100,000

Partial to full cover-age of most foreigncountries from late1930s to present

DIA, ATTN: DC-6C2, Washington,DC 20301

Low-, medium-,and high-altitudeaircraft

Black and white,color IR

Main scales:1:20,0001:40,000

Black and white:1:20,000 to1:120,000

Black and white:80% of US

Color IR:Partial US

ASCS, Aerial PhotoField Office, POBox 30010, SaltLake City, UT84130

Unmanned satel-lites ERTS LAND-SAT 1-5 MSS—

Band 4: green(0.5-0.6 m)

Band 5: red(0.7-0.8 m)

Band 6: near IR(0.7-0.8 m)

Band 7: near IR(0.8-1.0 m)

Black and white,color composite(IR), color compo-sition generation, 7and 9—track com-puter—compatibletapes (800 and1,600 bpi)

1:250,0001:3,369,000

Worldwide cover-age, completeearth’s surfacecoverage every 18days, 1972 to pres-ent; every 9 days,1975 to present

EROS data center

Manned spacecraftSkylab with S-190Amultispectral cam-era and S-190Bsystem, single lens(earth terrain cam-era)

S-190A: black andwhite, black andwhite IR, colorIR, high resolu-tion color

S-190B: black andwhite, color,stereo pairs

S-190A:1:1,250,0001:2,850,000

S-190B:1:125,0001:950,000

Limited worldwidecoverage

EROS data center

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Structural Geology 2-36

that is gathered in field investigations.Some of the most reliable methods avail-able for field investigation are boring, ex-ploration excavation, and geophysical ex-ploration.

Boring

Borings are required to characterizethe basic geologic materials at a project.They are broadly classified as disturbed,undisturbed, and core. Borings are occa-sionally made for purposes that do notrequire the recovery of samples, and theyare frequently used for more than onepurpose. Therefore, it is important tohave a complete log of every boring, evenif there is not an immediate use for someof the information. Initial explorationphases should concentrate on providingoverall information about the site.

Exploration Excavation

Test pits and trenches can be con-structed quickly and economically usingbulldozers, backhoes, draglines, or ditch-ing machines. Depths are normally lessthan 30 feet. Side excavations may re-quire shoring, if personnel must work inthe excavated areas. Exploratory tunnelsallow for detailed examination of thecomposition and the geometry of rockstructures such as joints, fractures, faults,and shear zones. Tunnels are helpful indefining the extent of the marginalstrength of rock or adverse rock struc-tures that surface mapping and boringinformation provide.

Geophysical Exploration

Geophysical exploration consists ofmaking indirect measurements from theearth’s surface or in boreholes to obtainsubsurface information. Boreholes orother subsurface explorations are neededfor reference and control when using geo-physical methods. Geophysical explora-tions are appropriate for rapidly locatingand correlating geologic features such as

stratigraphy, lithology, discontinuities,structure, and groundwater.

EQUIPMENT FOR FIELDDATA COLLECTION

The type of equipment needed on afield trip depends on the type of surveybeing conducted. The following items arealways required:

• Hammer. This is usually a geologichammer, and it is used to break ordig rock and soil and to preparesamples for laboratory examination.A hammer is also useful for deter-mining the strength and resistanceof the rock and the toughness of thegrains.

• Hand lens. A hand lens is a smallmagnifying glass, usually 10Xpower. It is used to examine indi-vidual mineral grains of rock foridentification, shape, and size.

• Dilute hydrochloric (HCl) acid. Onepart concentrated HCl acid to fourparts water is used to determinecarbonate rocks. Dilute acid is pre-ferred because the degree of its re-action with different substances isseen more easily.

• Brunton compass. One of the mostimportant pieces of equipment tothe field geologist is the Bruntoncompass. This instrument is an or-dinary magnetic compass with fold-ing open sights, a mirror, and a ro-tating dial graduated in degrees ormils. In some cases, the dial is num-bered to 360 degrees, while in oth-ers, the dial may be graduated in90-degree quadrants. A compasshelps measure dips, slopes, strikes,and directions of rock formations.

• Base map. A base map is essentialin all types of field work exceptwhen the plane-table-and-alidademethod is used.

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GEOLOGICAL SURVEYING

The instruments and methods of geo-logical surveying are numerous and var-ied. Instruments used on a particularproject depend on the scale, time, detail,and accuracy required.

Pace-and-Compass Method

The pace-and-compass method isprobably the least-accurate procedureused. The survey is conducted by pacingthe distance to be measured and deter-mining the angle of direction with thecompass. The field geologist records ele-vations on a topographic map, when it isavailable. When a topographic map or agood equivalent is unavailable, an aneroidbarometer or some type of accurate al-timeter is used to record elevations.

Plane-Table-and-Alidade Method

When accurate horizontal and verticalmeasurements are required, the plane-table-and-alidade method is used. Theequipment consists of a stadia rod, a tri-pod, a plane table, and an alidade. Sheetsof heavy paper are placed on the planetable to record station readings. After re-cording the stations, the geologist placesformation contacts, faults, and other mapsymbols on the paper. This informationcan later be transferred to a finished map.The alidade is a precision instrumentconsisting of a flat base that can easily bemoved on the plane table. The straightedge, along the side of the flat base andparallel to the line of sight, is used to plotdirections on the base map. The alidadealso consists of a telescopic portion with alens that contains one vertical hair andthree horizontal hairs (stadia hairs). Thevertical hair is used to align the stadiarod with the alidade. The horizontal hairsare used to read the distance to the rod.Vertical elevations are determined fromthe stadia distance and the vertical angleof the points in question.

Brunton-Compass-and-Aerial-PhotoMethod

A Brunton compass and a verticalaerial photo provide a rapid, accuratemethod for geological surveys. The aerialphoto is used in place of a base map. Con-tact, dips and strikes, faults, and otherfeatures may be plotted directly on theaerial photo or on a clear acetate overlay.Detailed notes of the geological featuresmust be kept in a separate field notebook.If topographic maps are available, theywill supplement the aerial photo andeliminate the need for an aneroid barome-ter. A topographic map may be used forthe base map and to plot control for hori-zontal displacements.

Plane-Table-, Mosaic-, and-AlidadeMethod

A mosaic of aerial photos may be usedwith a plane table and an alidade, thuseliminating the base map. This procedureis used to eliminate the rod holder and toaccelerate the mapping. By using a planetable and an alidade as a base, horizontaldistance does not have to be measured;and the surveyor can compute verticalelevation. The surveyor—

• Reads the angle of variation fromthe horizontal distance.

• Scales the distance from the map.

• Finds the difference by trigonomet-ric calculations.

This method is faster than the normalplane-table method, but it is not as accu-rate.

Photogeology Method

Photogeology is the fastest and least-expensive method of geological surveying.However, a certain amount of accuracyand detail is sacrificed. This type of sur-vey is normally used for reconnaissance of

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large areas. When a geologic map isconstructed from aerial-photo analysisalone, it shows only major structural

trends. After a preliminary office investi-gation, a geologist may go to the field anddetermine detailed geology of particularareas.

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CHAPTER 3

S u r f i c i a l G e o l o g y

An integral part of the military engineer’smission is the location and processing ofmaterials for construction use. Most con-struction materials are derived from rocksand soils that occur naturally on or near thesurface of the earth. These materials may beobtained by developing a quarry or a borrowpit.

Quarries are sites where open excavationsare made into rock masses by drilling, cut-ting, or blasting for the purpose of producingconstruction aggregate. These operations re-quire extensive time, manpower, andmachinery. Borrow pits are sites where un-consolidated material has been deposited andcan be removed easily by common earth-moving machinery, generally withoutblasting.

This chapter covers the processes that formsurficial features which are suitable forpotential borrow pit operations and the typesof construction materials found in these fea-tures.

FLUVIAL PROCESSThe main process responsible for the

erosion and subsequent deposition ofweathered material suitable for the develop-ment of borrow pits is that of moving water.When water moves very quickly, as over asteep gradient, it picks up weatheredmaterial and carries it away. When thestream slows down (for example, when thegradient is reduced), the capacity of the

stream to carry the weathered materialdecreases; then it deposits the material in avariety of possible surficial features.

Stream deposits are characteristicallystratified (layered) and composed of particleswithin a limited size range. Fluvial depositsare sorted by size based on the velocity of thewater. When the velocity of the stream fallsbelow the minimum necessary to carry theload, deposition occurs beginning with theheaviest material. In this way, rivers buildgravel and sandbars on the inside of meanderloops and dump fine silts and muds outsidetheir levees during floods. This createsdeposits of reasonably well-sorted, naturalconstruction materials.

Drainage PatternsWithout the benefit of geologic maps, it is

difficult to determine the type and structureof the underlying rocks. However, by study-ing the drainage patterns as they appear on atopographic map, both the rock structure andcomposition may be inferred.

Many drainage patterns exist; however,the more common patterns are—

Rectangular.Parallel.Dendritic.Trellis.Radial.Annular.Braided.

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Rectangular. This pattern is characterizedby abrupt, nearly 90-degree changes instream directions. It is caused by faulting orjointing of the underlying bedrock. Rectan-gular drainage patterns are generallyassociated with massive igneous andmetamorphic rocks, although they may befound in any rock type. Rectangular drainageis a specific type of angular drainage and isusually a minor pattern associated with amajor type, such as dendritic (see Figure3-1a). Angular drainage is characterized bydistinct angles of stream juncture.

Parallel. This drainage is characterized bymajor streams trending in the same direction,Parallel streams are indicative of gently dip-ping beds or uniformly sloping topography.Extensive, uniformly sloping basalt flows andyoung coastal plains exhibit this type ofdrainage pattern. On a smaller scale, theslopes of linear ridges may also reflect thispattern (see Figure 3-1b).

Dendritic. This is a treelike pattern, com-posed of branching tributaries to a mainstream. It is characteristic of essentially flat-lying and/or relatively homogeneous rocks(see Figure 3-1c).

Trellis. This is a modified version oft h edendritic pattern. Tributaries generally flowperpendicular to the main streams and jointhem at right angles. This pattern is found inareas where sedimentary or metamorphicrocks have been folded and the main streamsnow follow the strike of the rock (see Figure3-1d).

Radial. This pattern, in which streams flowoutward from a high central area, is found ondomes, volcanic cones, or round hills (see Fig-ure 3-1e).

Annular. This pattern is usually associatedwith radial drainage where sedimentaryrocks are upturned by a dome structure. Inthis case, streams circle around a high centralarea (see Figure 3-1f).

Braided. A braided stream pattern com-monly forms in arid areas during flash

Surficial Geology 3-2

flooding or from the meltwater of a glacier.The stream attempts to carry more materialthan it is capable of handling. Much of thegravels and sands are deposited as bars andislands in the stream bed (see Figure 3-1g andFigure 3-2, page 3-4), Figure 3-2 shows thevicinity of Valdez, Alaska. Both the Copperand Tonsina Rivers are braided streams.

DensityThe nature and density of the drainage pat-

tern in an area provides a strong indicator asto the particle size of the soils that havedeveloped. Sands and gravels are usuallyboth porous and permeable. This means thatduring periods of precipitation, water perco-lates down through the sediment. Thedensity of the drainage and the surface runoffare minimal due to this good internaldrainage.

Clays and silts are normally porous but notpermeable. Most precipitated water is forcedto run off, creating a fine network of streamerosion.

Sandstone and shale may exhibit the sametype of drainage pattern. Sandstone, due toits porosity and permeability, has good inter-nal drainage while shale dots not. Therefore,the texture or density of the drainage pattern—which develops on the sandstone is coarsewhile that on shale is fine.

Stream EvolutionThe likelihood of finding construction

materials in a particular stream valley can becharacterized by the evolution of that valley.The evolutionary stages are described as—

Youth.Maturity.Old age.

Youth. Youthful stream valleys, which arelocated in highland areas, are typified bysteep gradients, high water velocities withrapids and waterfalls present, downcutting instream bottoms resulting in the creation ofV-shaped valleys, and the filling of the entire

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valley floor by the stream (see Figure 3-3a).Although there is considerable erosion takingplace, there is very little deposition.

Maturity. A mature system has a developedfloodplain and, while the stream no longerfills the entire valley floor, it meanders toboth edges of the valley. The stream gradientis medium to low, deposition of materials canbe found, and (when compared with theyouthful stream) there is less downcuttingand more lateral erosion that contributes towidening the valley (see Figure 3-3b).

Old Age. In an old-age system, the streamgradient is very gentle, and the water velocityis low. The river exhibits little downcutting,and lateral meandering produces an exten-sive floodplain. Because of the low watervelocity, there is a great amount of deposition.

The river only occupies a small portion of thefloodplain (see Figure 3-3c).

Recognition of the stream evolution stage ofa particular river system is required todevelop sources of construction aggregate.Rivers in maturity or old age provide thegreatest quantities of aggregate. In youthfulrivers, sources of aggregate are often scarce orunobtainable due to the steep gradients andhigh velocity. Table 3-1, page 3-6, sum-marizes the characteristics of each stage ofstream evolution, Figure 3-4, page 3-7, showsan example of the topographic expression of ayouthful stream valley in the vicinity ofPortage, Montana. Figure 3-5, page 3-8,shows a mature stream valley in the vicinityof Fort Leavenworth, Kansas. Figure 3-6,page 3-9, shows an old age stream valley inthe vicinity of Philipp, Mississippi.

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Stream DepositsCoarse-grained (gravels and sands) and

fine-g-rained (silts and clays) deposits can befound by map reconnaissance. Certain surfi-cial features are comprised of coarse-grainedmaterials, others are made up of medium-sized particles, and still others of fine-g-rainedsediments. However, if the source area for astream is composed only of fine- grainedmaterials, then the resulting depositionalfeatures will also contain fine-grainedsediments, regardless of their usual composi-tion.

The following surficial features can be iden-tified by their topographic expressions onmilitary maps and are likely sources of con-struction materials.

Surficial Geology 3-6

Point bars.Channel bars.Oxbow lakes.Natural levees.BackSwamps/floodplains.Alluvial terraces.Deltas.Alluvial fans.

Point Bars. Meandering is the process bywhich a stream is gradually deflected from astraight-line course by slight irregularities.Most streams that flow in wide, flat-flooredvalleys tend to meander (bend). Thesestreams are alternately cutting and fillingtheir channels, and as the deflection progres-ses, the force of the flowing waterconcentrates against the channel wall on the

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outside of the curve. This causes erosion onthat wall (a body in motion tends to remain inmotion in the same direction and with thesame velocity until acted on by an externalforce) (see Figure 3-7). Consequently, there isa decrease in velocity and carrying power ofthe water on the inside of the curve, and thegravels and sands are deposited, formingpoint bar deposits (see Figure 3-8). Point bardeposits on many maps will not be apparentbut can be inferred to be at the inside of eachmeander loop.

Channel Bars. When a stream passesthrough a meander loop, its speed increaseson the outer bank due to the greater volume ofwater that is forced to flow on the outside ofthe loop. When the stream leaves themeander and the channel straightens out, theforces that caused the stream to move fasterare no longer in control and the stream slowsdown and deposits materials. Thesematerials are coarse-grained (gravels andsands) and are on the opposite bank anddownstream of the point bar. If there is aseries of meander loops, these deposits mayormay not be present between point bars,depending on the spacing of the meanders.However, a channel bar can be expected afterthe last meander loop. Figure 3-9, page, 3-12,shows channel bar deposits, oxbow lakes, andbackswamp/floodplain deposits in the vicinityof Fort Leavenworth, Kansas. A prominentchannel bar is located north of Stigers Island.

Mud Lake, Burns Lake, and HorseshoeLake are oxbow lakes. Backswamps on thefloodplain are represented by swampy groundsymbols.

Oxbow Lakes. During high-water stages, astream that normally flows through ameander loop may cut through the neck of apoint, thus separating the loop. When thishappens, the stream has taken the path ofleast resistance and has isolated the bend.The cutoff meander bend is eventually sealedfrom the main stream by fine deposits. Thebend itself then forms an oxbow lake (see Fig-ure 3-10, page 3-13). These deserted loopsmay become stagnant lakes or bogs, or thewater may evaporate completely leaving a U-shaped depression in the ground.Fine-grained deposits (silts and clays) arenormally located in oxbow lakes. An old pointbar deposit can be found on the inside of the U(see Figure 3-11, page 3-13). In Figure 3-9,page 3-12. Horseshoe Lake is an example ofthe topographic expression of an oxbow lake,

Natural Levees. Stream velocity increasesduring flooding as the stream swells withinthe confines of its bank to move a greatervolume of water. As the stream moves faster,it has the ability to carry more material. Ifthe volume of water becomes so great that thewater cannot stay in the channel, the streamspills over its banks onto the surrounding

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floodplain, which is a flat expanse of land ad-jacent to a stream or river. Once the streamspills over its banks, the water velocitydecreases as the water spreads out to occupya larger area. As the velocity decreases, sedi-ment carried by the floodwater is deposited.The size of this material depends primarily onthe character of the material in the sourcearea upstream and the velocity of the water inthe stream channel. Generally, gravels andsands can be found in a natural levee, withthe larger material deposited near the streambank and a gradual gradation to smaller sandparticles away from the stream.

Backswamps/Floodplains. After a floodends and the stream regresses into its chan-nel, much of the water that spilled over thebanks onto the floodplain is trapped on theoutside of the natural levees. The finematerials (silts and clays) that are suspendedin this water settle onto the floodplain. Con-sequently, these areas are often used foragricultural production. In the lower-lyingareas of the floodplain, a large amount of finesmay accumulate, inhibit drainage, and formswamplike conditions called a backswamp(see Figure 3-9, page 3-12).

Alluvial Terraces. A depositing streamtends to fill its valley with a fair amount of

granular alluvial material. If a change in thegeological situation results in the uplift of alarge area or rejuvenation of the stream, anincrease in the stream velocity by othermeans, or a change in the sedimentation anderosion process, the stream may begin toerode away the material it had deposited pre-viously. As the eroding stream meandersabout in its new valley, it may leave benchlikeremnants of the preexisting valley fillmaterial perched against the valley walls asterraces. This action of renewed downcuttingmay occur several times, leaving several ter-race levels (see Figure 3-12). These are easilyrecognized on a topographic map becausethey show up as flat areas with no contourlines, alternating with steeply sloping regionswith many contour lines. Alluvial terracesusually occur on one side of the stream butcan be found on both sides. They are a normalfeature of the history of any fluvial valley.They are usually a good source of sandsand gravels. Figure 3-13 shows alluvialterraces in the vicinity of Souris River, NorthDakota.

Deltas. When streams carrying sedimentsin suspension flow into a body of standingwater, the velocity of the stream is immedi-ately and drastically reduced. As a result, thesedimentary load begins to settle out of

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suspension, with the heavier particles set-tling first. If the conditions in the body ofwater (sea or lake) are such that these par-ticles are not spread out over a large area bywave action, or if they are not carried away bycurrents, they continue to accumulate at themouth of the stream. Large deposits of thesesediments gradually build up to just abovethe water level to form deltas (see Figure3-14). These assume three general forms,

depending mainly on the relative influence ofwaves, fluvial processes, and tides. Theseforms are—

Arcuate (see Figure 3-15a and b).Bird’s-foot (see Figure 3-15c,),Elongate (see Figure 3-15d).

Arcuate deltas are arc- or fan-shaped andare formed when waves are the primary forceacting on the deposited material. Arcuate

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deltas usually result from deposition bystreams carrying relatively coarse material(sands and gravels) with some occasional finematerial. Arcuate deltas consisting primar-ily of coarse material have very good internaldrainage; therefore, they have few minorchannels. On the other hand, an arcuatedelta having a considerable amount of finematerial (silts and clays) mixed with thecoarse material does not have good internaldrainage. In this case, a larger number ofminor channels develop. Generally, arcuatedeltas are considered good sources of sandsand gravels. An example of an arcuate deltais the Nile Delta in Egypt.

Bird’s-foot deltas are formed in situationswhere fluvial processes have a major in-fluence on deposited sediments. Bird’s-footdeltas resemble a bird’s foot from the air,hence the name. They are generally com-posed of fine-g-rained material and have verypoor internal drainage. These deltas are flatwith vegetation, have many small outlets,and are a good source of fine materials. TheMississippi Delta is a classic example of thisdelta type.

Elongate deltas form where tidal currentshave a major impact on sediment deposition.

They contain only a few distributaries, butthe distributaries that occur are large.

Alluvial Fans. These are the dry landcounterpart of deltas. They are formed bystreams flowing from rough terrain, such asmountains or steep faults, onto a flat plain.This type of deposit is found in regions thathave an arid to semiarid type of climate, suchas the western interior, the Basin and RangeProvince of the United States, and the desertmountain areas worldwide. The valleys inthese areas are normally dry much of theyear, with streams resulting only after tor-rential rainstorms or following the springsnow melt. The mountains themselves aredevoid of vegetation, and erosion by thestreams is not impeded. These streams rushdown a steep gradient, and when they meetthe valley floor, there is a sudden reduction invelocity. The sediment load is deposited atthe foot of the rough terrain. This deposit isin the form of a broad “semitone” with theapex pointing upstream. Coalescing alluvialfans consist of a series of fans that have joinedto form one large feature. This is typical inarid areas. Figure 3-16 depicts alluvial andcoalescing alluvial fans. Alluvial fans maybe readily identified by their topographic

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expressions of concentric half-circular con-tour lines. Figure 3-17 is a topographic mapshowing the Cedar Creek alluvial fan in thevicinity of Ennis Lake, Montana. This al-luvial fan is approximately four miles inradius. Figure 3-18, page 3-20, shows coalesc-ing alluvial fans in the vicinity of Las Vegas,Nevada.

The types of materials found in alluvialfans are gravels, sands, and fines based on a1/3 rule. The first 1/3, the area adjacent tothe highland, is primarily composed ofgravels; the middle 1/3 is composed of sands;and the final 1/3, the area farthest from thehighland, is composed of fines.

Fluvial features are found throughout theworld and are the primary source of borrowpit materials for military engineers. Table3-2, page 3-21, and Figure 3-19, page 3-21,present a summary of fluvial features. Fig-ure 3-20, page 3-22, shows a generalizeddistribution of fluvial surficial featuresthroughout the world.

GLACIAL PROCESSBetween ten and twenty-five thousand

years ago, much of North America, Europe,and Northern Asia was covered by glaciers.Significant ice sheets still cover Greenlandand Antarctica, and lesser ice sheets can befound at high elevations and latitudes (seeFigure 3-21, page 3-23).

Glaciation produces great changes in theexisting topography by reshaping the landsurface and depositing new surficial featuresthat may serve as a source of construction ag-gregate for military engineers.

Types of GlaciationThe glaciation process may be described as

either continental or alpine glaciation.

Continental. Continental glaciation occurson a large, regional scale affecting vast areas.It may be characterized by the occurrence ofmore depositional features than erosionalfeatures. Continental glaciers can be oftremendous thickness and extent. They

move slowly in a plastic state with the icechurning the soil and rocks beneath it as wellas crushing and plucking rocks from theground and incorporating large amounts ofmaterial within the glacier itself. The overallrange of particle size of these materials isfrom clays through cobbles and boulders (seeFigure 3-22, page 3-24).

Alpine. Alpine or mountain glaciation takesplace in mountainous areas and generallyresults in the creation of mainly erosionalforms. Alpine glacial features are very dis-tinctive and easy to recognize. In the past,glaciers scooped out and widened the valleysthrough which they moved, producing valleyswith a U-shaped profile in contrast to theV-shaped profile produced by fluvial erosion(see Figure 3-23, page 3-25).

Glacial DepositsMaterials deposited by glaciers are fre-

quently differentiated into two types. Theyare—

Stratified.Unstratified.

Stratified. The features composed ofstratified deposits are actually the result ofdeposition of sediment by glacial streams(glaciofluvial) and not by the movement of theice itself. These features are—

Outwash plains.Eskers.Kames.Kame terraces.Glacial lake deposits.

They result when the material in the glacierhas been carried and deposited by meltwaterfrom the glacier. The water selectivelydeposits the coarsest materials, carryingthe fines away from the area. The endresult is essentially deposits of sands andgravels.

Outwash plains result when melting ice atthe edge of the glacier creates a great volumeof water that flows through the end moraineas a number of streams rather than as a con-tinuous sheet of water. Each of the streams

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builds an alluvial fan and each of the fansjoins together and forms a plain that slopesgently away from the end moraine area. Thecoarsest materiaI is deposited nearest the endmoraine, and the fines are deposited atgreater distances. Much of the prairie land inthe United States consists of outwash plains.Drainage and trafficability in the outwashplains are much better than in a groundmoraine; however, kettles can be formed in

outwash plains due to large masses of ice leftduring the recession of the ice front. If thekettles are numerous, the outwash area iscalled a pitted plain (see Figure 3-22, page3-24).

Eskers are winding ridges of irregularlystratified sands and gravels that are foundwithin the area of the ground moraine. Theridges are usually several miles long but are

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rarelv more than 45 to 60 feet wide or morethan 150 feet high. They are formed by waterthat flowed in tunnels or ice-walled gorges inor beneath the ice. They branch and wind likestream valleys but are not like ordinary val-leys in that they may cross normal drainagepatterns at an angle, and they may also passover hills (see Figures 3-22, page 3-24, andFigure 3-24, page 3-26). Figure 3-24, page3-26, shows kettle lakes, swamps, and es-kers.

A similar feature that resembles an esker,but is rarely more than a mile in length, is aridge known as a crevasse filling. A crevasseis a large, deep crevice or fissure on the sur-face of a glacier. Unsorted debris washes intothe crevasse, and when the surrounding icemelts, a ridge containing a considerableamount of fines is left standing.

Kames are conical hills of sands andgravels deposited by heavily laden glacialstreams that flowed on top of or off of theglacier. They are usually isolated hills thatare associated with the end or recessional

moraine; kettle lakes are commonly found inthe same area. The formation of kames nor-mally occurred when meltwater streamsdeposited relatively coarse materials in theform of a glacioalluvial fan at the edge of theice; the fine particles were washed away.This material accumulated along the side ofthe ice, and when the ice receded, thematerial slumped back on the side formerly incontact with the glacier.

Delta kames are another type of kame thatmay be formed when the meltwater flows intoa marginal lake and forms a delta. After thelake and the ice disappear, deltas are left asflat-topped, steep-sided hills of well-sortedsands and gravels (see Figure 3-22, page3-24).

Kame terraces are features associated withalpine glaciation. When the ice moves down avalley, it is in contact with the sides of the val-ley. As the glacier melts away from the valleywall, glacial water flows into the spacecreated between the side of the glacier and thevalley wall. The void is filled with gravels and

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sands, while the fines are carried away by thestream water. A terrace is left where the icewas in contact with the valley; gravels andsands can be found at the base of the terrace(see Figure 3-25).

Glacial lake deposits occur during the melt-ing of the glacier when many lakes and pondsare created by the meltwater in the outwashareas. The streams that fed these waterswere laden with glacial material. Most of thegravels and sands that were not depositedbefore reaching the lake accumulated as adelta (later to be called a delta kame) aftermelting of the ice. The fines that remainedsuspended in the water were, on the otherhand, deposited throughout the lake. Duringthe summer, a band consisting of light-colored, coarse silt was deposited, whereas athinner band of darker, finer-grainedmaterial was deposited in the winter. Thetwo bands together represent a time span ofone year and are referred to as a varve.

Unstratified. Unstratified glacial deposits(sediments deposited by the ice itself) are themost common of the of glacial deposits. Theycomprise the following surfical features:

Ground moraines.End moraines.

Recessional moraines.Drumlins.

Unstratified deposits make up landformsthat may be readily identified in the field, onaerial photographs, and from topographicand other maps. Unstratified deposits arecomposed of a heterogeneous mixture of par-ticle types and sizes ranging from clays toboulders. Till is the name given to this mix-ture of materials. It is the most widespread ofall the forms of glacial debris. In general, fea-tures comprised of till are undesirable assources of military construction aggregatesince the material must be washed andscreened to provide proper gradation.

Ground moraines, sometimes called tillplains, are deposits that are laid down aS theglacier recedes. Melting ice drops materialthat blankets the area over which the glaciertraveled. A deposit of this kind forms gentlyrolling plains. The deposit itself may be athin veneer of material lying on the bedrock,or it may be hundreds of feet thick. Morainesoil composition is complex and often indeter-minate. This variation in sediment makeupis due to the large variety of rocks and soilpicked up by the moving glacier (see Figure3-22, page 3-24).

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Morainic areas have a highly irregulardrainage pattern because of the haphazardarrangement of ridges and hills, althougholder till plains tend to develop dendritic pat-terns. Frequent features associated withgrouncl moraines are kettle holes andswamps. Kettles are usually formed by themelting of ice that had been surrounded by orembedded in the moraine material. Largeamounts of fines in the till prevent water frompercolating down through the soil. This mayallow for the accumulation of water in the ket-tle holes forming kettle lakes or, in low-lyingareas, swamps. Figure 3-22, page 3-24, andFigure 3-24, page 3-26, show ground morainewith an esker.

End moraines, sometimes called terminalmoraines, are ridges of till material that werepushed to their locations at the limit of theglacier’s advance by the forceful action of theice sheet. Generally, there is no one linearelement, such as a continuous ridge, evidentin either the field or on aerial photos. Nor-mally. this deposit appears as adiscontinuous chain of elongated to oval hills.These hills vary in height from tens tohundreds of feet. The till material is. attimes. quite clayey. Kettle lakes are some-times associated with terminal morainedeposits also (see Figure 3-22, page 3-24).

Recessional moraines. which are similar toend moraines. are produced when a recedingglacier halts its retreat for a considerableperiod of time. The stationary action allowsfor the accumulation of till material along theglacier’s edge. A series of these moraines may

result during the retreat of a glacier (see Fig-ure 3-22, page 3-24).

Drumlins are asymmetrical, streamlinedhills of gravel till deposited at the base of aglacier and oriented in a direction parallel toice flow. The stoss side (the side from whichthe ice flowed) of the drumlin is steeper andblunter than the lee side. The overall ap-pearance of a drumlin resembles an invertedspoon if viewed from above. Drumlins com-monly occur in groups of two or more.Individual drumlins are seldom more than½ mile long, and they can rise to heights of75 to 100 feet (see Figure 3-26 and Figure3-27).

It is important to understand that featuresformed from the glacial process only occur incertain areas of the world. Figure 3-28, page3-30, and Figure 3-29, page 3-31, illustratethe regions of the United States and the worldwhere glacial landforms occur. Table 3-3,page 3-32, is a summary of glacial surficialfeatures.

EOLIAN PROCESSIn arid areas where water is scarce, wind

takes over as the main erosional agent. Whena strong wind passes over a soil, it carriesmany particles of soil with it. The height anddistance the materials are transported is afunction of the particle size and the windvelocity. The subsequent decrease in thewind velocity gives rise to a set of wind-bornedeposits called eolian features.

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Types of Eolian ErosionThere are two types of wind erosion. They

are—Deflation.Abrasion.

Deflation. Deflation occurs when loose par-ticles are lifted and removed by the wind.This results in a lowering of the land surfaceas materials are carried away. Unlike streamerosion, in which downcutting is limited by a“base level” (usually sea level), deflation cancontinue lowering a land surface as long as ithas loose material to carry away. Deflationmay be terminated if the land surface is cutdown to the water table (moist soil is not car-ried away as easily) or if vegetation issufficient to hold the soil in place. In addi-tion, deflation may be halted when the supplyof fine material has been depleted. Thismakes a surface of gravel in the area wheredeflation has taken place. This gravel surfaceis known as desert pavement (see Figure 3-30,page 3-32).

Abrasion. Abrasion occurs when hard par-ticles are blown against a rock face causingthe rocks to break down. As fragments arebroken off, they are carried away by the wind.This process can grind down and polish rocksurfaces. A rock fragment with facets thathave been cut in this way is called a ventifact(see Figure 3-31, page 3-33).

Modes of TransportationSoil particles can be carried by the wind in

the following ways:

Bed Load. Material that is too heavy to becarried by the wind for great distances at atime (mainly sand-sized particles) bouncesalong the ground, rarely higher than two feet.

Suspended Load. These are fines (mostlysilts) that are easily carried by the wind.Suspended loads extend to high altitudes(sometimes thousands of feet) and can betransported for thousands of miles. During aparticularly bad dust storm in the mid-western “dust bowl” on 20 March 1935, the

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suspended load extended to altitudes of over Figure 3-32 illustrates the origin of these12,000 feet. The lowermost mile of the atmos-phere was estimated to contain over 166,000tons of suspended particles per cubic mile.Enough material was transported to bringtemporary twilight to New York and NewEngland (over 2,000 miles away) on 21March.

Eolian FeaturesEolian surficial features may consist of

gravels, sands, or fines. The three main typesof eolian features are-

Lag deposits or desert pavement.Sand dunes.Loess deposits.

deposits.

Lag Deposits or Desert Pavement. As thewind billows across the ground, sands andfines are continually removed. Eventually,gravels and pebbles that are too large to becarried by the wind cover the surface. Theseremnants accumulate into a sheet that ul-timately covers the finer-grained materialbeneath and protects it from further defla-tion. Desert pavement usually developsrapidly on alluvial fan and alluvial terracesurfaces. The exposed surface of the gravelsmay become coated with a black, glittery sub-stance termed desert varnish. In some

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locations, the evaporation of water, broughtto the surface by the capillary action of thesoil, may leave behind a deposit of calciumcarbonate (caliche) or gypsum. It acts as a ce-ment, hardening the pavement into aconglomeratelike slab.

Although desert pavement contains goodgravel material, the layers are normally toothin to supply the quantity required for con-struction. However, it does provide a roughbut very trafficable surface for all types ofvehicles and also provides excellent airfields.

Sand Dunes. Dunes may take severalforms, depending on the supply of sand, thelay of the land, vegetation restrictions, andthe steady direction of the wind. Theirgeneral expressions are as follows:

Transverse.Longitudinal.Barchan.Parabolic.Complex.

Transverse dunes are wavelike ridges thatare separated by troughs; they resemble seawaves during a storm. These dunes, whichare oriented perpendicular to the prevailingwind direction, occur in desert locationswhere a great supply of sand is present overthe entire surface. A collection of transversedunes is known as a sand sea (see Figure3-33a, page 3-34).

Longitudinal dunes have been elongated inthe direction of the prevailing winds. Theyusually occur where strong winds blow acrossareas of meager amounts of sand or where thewinds compete with the stabilizing effect ofgrass or small shrubs (see Figure 3-33b, page3-34).

Barchan dunes are the simplest and mostcommon of the dunes. A barchan is usuallycrescent-shaped, and the windward side has agentle’ slope rising to a broad dome that cutsoff abruptly to the leeward side. Barchansform in open areas where the direction of thewind is fairly constant and the ground is flatand unrestricted by vegetation and topog-raphy (see Figure 3-33c, page 3-34).

Parabolic, or U-shaped, dunes have tipsthat point upwind. They typically form alongcoastlines where the vegetation partiallycovers the sand or behind a gap in anobstructing ridge. Later, a parabolic dunemay detach itself from the site of formationand migrate independently (see Figure 3-33d,page 3-34).

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Complex dunes lack a distinct form anddevelop where wind directions vary, sand isabundant, and vegetation may interfere.These can occur locally when other dunetypes become overcrowded and overlap,thereby losing their characteristic shapes in adisorder of varying slopes (see Figure 3-33e).

Loess Deposits. In a number of regions ofthe world, thick accumulations of yellowish-brown material composed primarily ofwindblown silts make up a substantialamount of surface area. These deposits areknown as loess. The material that makes upthese deposits originated mainly from driedglacial outwash, floodplains, or desert areafines. Loess is composed of’ physically groundrock rather than of chemically weathered

the deposits may range in thickness from afew feet to hundreds of feet. Thickness tendsto decrease with distance from the source. Inthe United States, most of Kansas, Nebraska,Iowa, and Illinois are covered by loess. Aftera loess has been laid down, it is rarely pickedup again. This is due to a very thin layer offines that interlock after wetting. While dryloess is trafficable, it loses all strength with aslight amount of water (see Figure 3-34).

Eolian features occur worldwide and mayconsist of areas of sand dunes and desertpavement or loess; however, their topogra-phic expressions vary. In general, dune areasare specified on maps by special topographicsymbols since they are continually chang-ing unless stabilized by vegetation. Figure3-35, page 3-36, is a topographic expres-sion, using special symbols, of sand

material. The source and deposition point forthe material may be many miles apart, and

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dunes and desert pavement (Summan). Fig- provide construction aggregate to meet mis-ure 3-36 shows the generalized distribution sion requirements. Generally, engineer unitsof eolian landforms throughout the world. attempt to develop borrow pit operations in

fluvial features since they are easy to identifySOURCES OF CONSTRUCTION and are normally accessible. In arid and

AGGREGATE semiarid regions, eolian deposits and alluvialMilitary engineers use their knowledge of fans provide large amounts of aggregate. In

surficial features to develop borrow pits and mountainous regions and continentally

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glaciated regions, fluvial-glacial deposits can materials. Table 3-4 summarizes the types ofprovide large quantities of quality aggregate. aggregates found in common fluvial, glacial,Therefore, their presence should not neces- and eolian surficial features.sarily be discounted in preference to fluvial

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CHAPTER 4

S o i l F o r m a t i o n a n d

C h a r a c t e r i s t i c s

The term “soil,” as used by the US Army,refers to the entire unconsolidated materialthat overlies and is distinguishable frombedrock. Soil is composed principally of thedisintegrated and decomposed particles ofrock. It also contains air and water as well asorganic matter derived from the decomposi-tion of plants and animals. Bedrock isconsidered to be the solid part of the earth’scrust, consisting of massive formationsbroken only by occasional structural failures.Soil is a natural conglomeration of mineralgrains ranging from large boulders to singlemineral crystals of microscopic size. Highlyorganic materials, such as river bottom mudand peat, are also considered soil. To helpdescribe soils and predict their behavior, themilitary engineer should understand thenatural processes by which soils are formedfrom the parent materials of the earth’s crust.As soils are created, by the process of rockweathering and often by the additionalprocesses of transportation and disposition,they often acquire distinctive characteristicsthat are visible both in the field and on mapsand photographs.

Section I. Soil Formation

WEATHERINGWeathering is the physical or chemical

breakdown of rock. It is this process by whichrock is converted into soil. Weathering isgenerally thought of as a variety of physical or

chemical processes that are dependent on theenvironmental conditions present.

Physical ProcessesPhysical weathering is the disintegration of

rock. Physical weathering processes breakrock masses into smaller and smaller pieceswithout altering the chemical composition ofthe pieces. Therefore, the disintegrated frag-ments of rock exhibit the same physicalproperties as their sources. Processes thatproduce physical weathering are—

Unloading.Frost action.Organism growth.Temperature changes.Crystal growth.Abrasion.

Unloading. When rock layers are buriedunder the surface, they are under compres-sive stress from the weight of overlyingmaterials. When these materials areremoved, the resulting stress reduction mayallow the rock unit to expand, forming ten-sional cracks (jointing) and causing extensivefracturing.

Frost Action. Most water systems in rocksare open to the atmosphere, but freezing atthe surface can enclose the system. When theenclosed water freezes, it expands nearly one-tenth of its volume, creating pressures up to

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4,000 pounds per square inch (psi). The ex-panding ice fractures the rock.

Organism Growth. Trees and plantsreadily grow in the joints of rock masses nearthe surface. The wedging action caused bytheir root growth hastens the disintegrationprocess.

Temperature Changes. Daily or seasonaltemperature changes can cause differentialexpansion and contraction of rocks near theearth’s surface. This results in a tensionalfailure called spalling or exfoliation. As therock’s surface heats up, it expands; as it cools,it contracts. The jointing patterns of igneousrock are often the result of tern perature chan-ges.

Crystal Growth. The growth of mineralsprecipitating from groundwater can applypressure similar to that of expanding ice.Soluble minerals, such as halite (salt), readilycrystallize out of solution.

Abrasion. Sediments suspended in wind orfast-moving water can act as abrasives tophysically weather rock masses. Rock par-ticles carried by glacial ice can also be veryabrasive.

Chemical ProcessesChemical weathering is the decomposition

of rock through chemical processes. Chemi-cal reactions take place between the mineralsof the rock and the air, water, or dissolved orsuspended chemicals in the atmosphere.Processes that cause chemical weatheringare—

Oxidation.Hydration.Hydrolysis.Carbonation.Solution.

Oxidation. Oxidation is the chemical unionof a compound with oxygen. An example isrusting, which is the chemical reaction ofoxygen, water, and the iron mineral pyrite(FeS2) to form ferrous sulfate (FeSO4).Oxidation is responsible for much of the red

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and yellow coloring of soils and surface rockbodies. This type of reaction is important inthe decomposition of rocks, primarily thosewith metallic minerals.

Hydration. Hydration is the chemical unionof a compound with water. For example, themineral anhydrite (CaSO4) incorporateswater into its structure to form the newmineral gypsum (CaSO4·2H2O).

Hydrolysis. This decomposition reaction isrelated to hydration in that it involves water.It is a result of the partial dissociation ofwater during chemical reactions that occur ina moist environment. It is one of the types ofweathering in a sequence of chemical reac-tions that turns feldspars into clays. Anexample of hydrolysis is the altering ofsodium carbonate (Na2CO3) to sodiumhydroxide (NaOH) and carbonic acid(H2CO3).

Carbonation. This is the chemical processin which carbon dioxide from the air uniteswith various minerals to form carbonates. Acopper penny eventually turns green from theunion of copper with carbon dioxide in the airto form copper carbonate. Carbonate rocks,in turn, are susceptible to further weatheringprocesses, namely solution.

Solution. Carbon dioxide dissolved in waterforms a weak acid called carbonic acid(H2CO3). Carbonic acid acts as a solvent todissolve carbonates, such as limestone, andcarry them away. This creates void spaces, orcaves, in the subsurface. Areas that have un-dergone extensive solutioning are known askarst regions.

DISCONTINUITIES AND WEATHERINGJointing and other discontinuities increase

the surface area of the rock mass exposed tothe elements and thereby enhance chemicalweathering. Discontinuities, such as joints,faults, or caverns, act as conduits into therock mass for the weathering agents (air andwater) to enter. Weathering occurs on ex-posed surfaces, such as excavation walls, roadcuts, and the walls of discontinuities. Theeffect of weathering along discontinuities is a

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general weakening in a zone surrounding thewall surface.

EFFECTS OF CLIMATEThe climate determines largely whether a

type of rock weathers mostly by chemical ormostly by physical processes. Warm, wet(tropical or subtropical) climates favor chemi-cal weathering. In such climates, there isabundant water to support the various chemi-cal processes. Also, in warm, wet climates,the temperature is high enough to allow thechemical reactions to occur rapidly. Cold, dryclimates discourage chemical weathering ofrock but not physical weathering. The in-fluence of climate on the weathering of themany rock types varies; however, most rocktypes weather more rapidly in warm, wetclimates than in cold and/or dry climates.

EFFECTS ON RELIEFFEATURES

Weathering combined with erosion (thetransportation of weathered materials) isresponsible for most of the relief features onthe earth’s surface. For example, the subsur-face cavities so predominant in karst regionsdevelop along the already existing joints andbedding planes and commonly form an inter-lacing network of underground channels. Ifthe ceiling of one of these subterranean voidspaces should collapse, a sinkhole forms atthe earth’s surface. The sinkhole may rangein size from a few feet to several miles indiameter. It may be more than a hundred feetdeep, and it may be dry or contain water. Ex-tensive occurrences of sinkholes result in theformation of karst topography, which is char-acterized by a pitted or pinnacle groundsurface with numerous depressions and apoorly developed drainage pattern. Otherfeatures associated with karst topography in-clude:

Lost or disappearing streams wheresurface streams disappear or flow un-derground.Rises where underground streamssuddenly reappear at the surface toform springs.

Solution cavities and sinkholes can bedetrimental to foundations for horizontal andvertical construction and should be identifiedand evaluated for military operations.

SOIL FORMATION METHODSSoils may be divided into two groups based

on the method of formation—residual soilsand transported soils.

Residual SoilsWhere residual soils are formed, the rock

material has been weathered in place. Whilemechanical weathering may occur, chemicalweathering is the dominant factor. As aresult of this process, and because the rockmaterial may have an assorted mineral struc-ture, the upper layers of soils are usuallyfine-grained and relatively impervious towater. Under this fine-grained material is azone of partially disintegrated parent rock. Itmay crumble easily and break down rapidlywhen exposed to loads, abrasions, or furtherweathering. The boundary line between soiland rock is usually not clearly defined.Lateritic soils (highly weathered tropical soilscontaining significant amounts of iron or ironand aluminum) are residual. Residual soilsgenerally present both drainage and founda-tion problems. Residual soil deposits arecharacteristically erratic and variable in na-ture. Figure 4-1, page 4-4, shows a typicalresidual soil.

Transported SoilsBy far, most soils the military engineer en-

counters are materials that have beentransported and deposited at a new location.Three major forces—glacial ice, water, andwind —are the transporting agents. Theseforces have acted in various ways and haveproduced a wide variety of soil deposits.Resulting foundations and constructionproblems are equally varied. These soils maybe divided into glacial deposits, sedimentaryor water-laid deposits, and eolian or wind-laiddeposits. Useful construction material can belocated by being able to identify these fea-tures on the ground or on a map (see Chapter3).

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SOIL PROFILESAs time passes, soil deposits undergo a

maturing process. Every soil depositdevelops a characteristic profile because ofweathering and the leaching action of wateras it moves downward from the surface. Theprofile developed depends not only on the na-ture of the deposit but also on factors such astemperature, rainfall amounts, and vegeta-tion type. Under certain conditions, complexprofiles may be developed, particularly withold soils in humid regions. In dry regions, theprofile may be obscured.

Typical soil profiles have at least threelayers, known as horizons (see Figure 4-2).They are-

A horizon.B horizon.C horizon.

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The A horizon, or upper layer, contains azone of accumulation of organic materials inits upper portion and a lower portion oflighter color from which soil colloids and othersoluble constituents have been removed. TheB horizon represents the layer where solublematerials accumulate that have washed outof the A horizon. This layer frequently con-tains much clay and may be several feet thick.The C horizon is the weathered parentmaterial. The development of a soil profiledepends on the downward movement ofwater. In arid and semiarid regions, themovement of water may be reversed andwater may be brought to the surface becauseof evaporation. Soluble salts may thus bebrought to the surface and deposited.

The study of the maturing of soils and therelationship of the soil profile to the parent

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material and its environment is called pedol-ogy. As will be explained later, soils may beclassified on the basis of their soil profiles.This approach is used by agricultural soilscientists and some engineering agencies.This system is of particular interest to en-gineers who are concerned with road andairfield problems.

Soils not only characteristically vary withdepth, but several soil types can and often doexist within a relatively small area. Thesevariations may be important from an en-gineering standpoint. The engineeringproperties of a soil are a function not only ofthe kind of soil but also of its conditions.

Section II. Soil Characteristics

PHYSICAL PROPERTIESThe engineering characteristics of soil vary

greatly, depending on such physical proper-ties as—

Grain or particle size.

Gradation.Particle shape.Structure.Density.Consistency.

These properties are defined, in most casesnumerically, as a basis for the systematicclassification of soil types. Such a classifica-tion system, used in connection with acommon descriptive vocabulary, permits theready identification of soils that may be ex-pected to behave similarly.

The nature of any given soil can be changedby manipulation. Vibration, for example, canchange a loose sand into a dense one. There-fore, the behavior of a soil in the field dependsnot only on the significant properties of the in-dividual constituents of the soil mass but alsoon properties due to particle arrangementwithin the mass.

Frequently, the available laboratory equip-ment or other considerations only permit the

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military engineer or the engineer’s soil tech-nician to determine some of the soil’sproperties and then only approximately.Hasty field identification often permits a suf-ficiently accurate evaluation for the problemat hand. However, the engineer cannot relysolely on experience and judgment in estimat-ing soil conditions or identifying soils. Hemust make as detailed a determination of thesoil properties as possible and subsequentlycorrelate these identifying properties withthe observed behavior of the soil.

Grain or Particle SizeIn a natural soil, the soil particles or solids

form a discontinuous mass with spaces orvoids between the particles. These spaces arenormally filled with water and/or air. Or-ganic material may be present in greater orlesser amounts. The following paragraphsare concerned with the soil particles themsel-ves. The terms “particle” and “grain” areused interchangeably.

Detemination. Soils may be grouped onthe basis of particle size. Particles aredefined according to their sizes by the use ofsieves, which are screens attached to metalframes. Figure 4-3 shows sieves used for theUnified Soil Classification System (USCS). Ifa particle will not pass through the screenwith a particular size opening, it is said to be“retained on” that sieve. By passing a soilmixture through several different size sieves,it can be broken into its various particle sizesand defined according to the sieves used.Many different grain-size scales have beenproposed and used. Coarse gravel particlesare comparable in size to a lemon, an egg, or awalnut, while fine gravel is about the size of apea. Sand particles range in size from that ofrock salt, through table salt or granulatedsugar, to powdered sugar. Below a Number200 sieve, the particles (fines) are designatedas silts or clays, depending on their plasticitycharacteristics.

Other grain-size scales apply other limits ofsize to silts and clays. For example, some civilengineers define silt as material less than0.05 mm in diameter and larger than 0.005mm. Particles below 0.005 mm are clay sizes.

A particle 0.07 mm in diameter is about assmall as can be detected by the unaided eye.It must be emphasized that below the Num-ber 200 sieve (0.074-mm openings), particlesize is relatively unimportant in most casescompared to other properties. Particlesbelow 0.002 mm (0.001 mm in some grain-sizescales) are frequently designated as soil col-loids. The organic materials that may bepresent in a soil mass have no size boun-daries.

Several methods may be used to determinethe size of soil particles contained in a soilmass and the distribution of particle sizes.Dry sieve analysis has sieves stacked accord-ing to size, the smallest being on the bottom.Numbered sieves designate the number ofopenings per lineal inch. Dimensioned sievesindicate the actual size of the opening. Forexample, the Number 4 standard sieve hasfour openings per lineal inch (or 16 openingsper square inch), whereas the ¼-inch sievehas a sieve opening of ¼ inch.

The practical lower limit for the use ofsieves is the Number 200 sieve, with 0.074 -millimeter-square openings. In someinstances, determining the distribution of

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particle sizes below the Number 200 sieve isdesirable, particularly for frost susceptibilitydetermination. This may be done by aprocess known as wet mechanical analysis,which employs the principle of sedimenta-ion. Grains of different sizes fall through aliquid at different velocities. The wetmechanical analysis is not a normal fieldlaboratory test. It is not particularly impor-ant in military construction, except that thepercentage of particles finer than 0.02 mmhas a direct bearing on the susceptibility ofsoil to frost action. A field method for per-forming a wet mechanical analysis for thedetermination of the percentage of materialfiner than 0.02 mm is given in TechnicalManual (TM) 5-530. The procedure is calleddecantation.

The procedures that have been describedabove are frequently combined to give a morecomplete picture of grain-size distribution.The procedure is then designated as a com-bined mechanical analysis.

Other methods based on sedimentation arefrequently used in soils laboratories, par-ticularly to determine particle distributionbelow the Number 200 sieve. One suchmethod is the hydrometer analysis. A com-plete picture of grain-size distribution isfrequently obtained by a combined sieve andhydrometer analysis. This method isdescribed in TM 5-530 (Section V).

Reports. Test results may be recorded in oneof the following forms:

Tabular (see Figure 4-4, page 4-8).Graphic (see Figure 4-5, page 4-9).

The tabular form is used most often on soilconsisting predominantly of coarse particles.This method is frequently used when the soilgradation is being checked for compliancewith a standard specification, such as for agravel base or a wearing course.

The graphic form permits the plotting of agrain-size distribution curve. This curve af-fords ready visualization of the distributionand range of particle sizes. It is also par-ticularly helpful in determining the soil

classification and the soil’s use as a founda-tion or construction material.

GradationThe distribution of particle sizes in a soil is

known as its gradation. Gradation and otherassociated factors, primarily as applicable tocoarse-grained soils, are discussed in the fol-lowing paragraphs.

Effective Size. The grain size correspondingto 10 percent passing on a grain-size distribu-tion curve (see Figure 4-5, page 4-9) is calledHazen’s effective size. It is designated by thesymbol D10. For the soil shown, D10 is 0.13mm. The effective sizes of clean sands andgravels can be related to their permeability.

Coefficient of Uniformity. The coefficientof uniformity (Cu) is defined as the ratiobetween the grain diameter (in milli-meters) corresponding to 60 percent passingon the curve (D60) divided by the dia-meter of the 10 percent (D10) passing.Hence, Cu = D60/D10.

For the soil shown on Figure 4-5, page 4-9—D60 = 2.4 mm and D10 = 0.13 mm

then Cu = 2.4/0.13 = 18.5

The uniformity coefficient is used to judgegradation.

Coefficient of Curvature. Another quan-tity that may be used to judge the gradation ofa soil is the coefficient of curvature, desig-nated by the symbol Cc.

D10 and D60 have been defined, while D30 isthe grain diameter corresponding to 30 per-cent passing on the grain-size distributioncurve. For the soil shown in Figure 4-5, page4-9:

D30 = 0.3 mm

Well-Graded Soils. A well-graded soil isdefined as having a good representation of all

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particle sizes from the largest to the smallest(see Figure 4-6), and the shape of the grain-size distribution curve is considered“smooth.” In the USCS, well-graded gravelsmust have a Cu value >4, and well-gradedsands must have a Cu value > 6. For well-graded sands and gravels, a Cc value from 1to 3 is required. Sands and gravels notmeeting these conditions are termed poorlygraded.

Poorly Graded Soils. The two types ofpoorly graded soils are—

Uniformly graded.Gap-graded.

A uniformly graded soil consists primarily ofparticles of nearly the same size (see Figure4-7). A gap-graded soil contains both largeand small particles, but the gradation con-tinuity is broken by the absence of someparticle sizes (see Figure 4-8).

Figure 4-9 shows typical examples of well-graded and poorly graded sands and gravels.Well-graded soils ((GW) and (SW) curves)

would be represented by a long curve span-ning a wide range of sizes with a constant orgently varying slope. Uniformly graded soils((SP) curve) would be represented by a steeplysloping curve spanning a narrow range ofsizes; the curve for a gap-graded soil ((GP)curve) flattens out in the area of the grain-size deficiency.

Bearing Capacity. Coarse materials thatare well-graded are usually preferable forbearing from an engineering standpoint,since good gradation usually results inhigh density and stability. Specificationsfor controlling the percentage of thevarious grain-size groups required for awell-graded soil have been established forengineering performance and testing. Byproportioning components to obtain awell-graded soil, it is possible to providefor maximum density. Such proportion-ing develops an “interlocking” of particleswith smaller particles filling the voids be-tween larger particles, making the soilstronger and more capable of supportingheavier loads. Since the particles are“form-fitted”, the best load distributiondownward will be realized. When eachparticle is surrounded and “locked” byother particles, the grain-to-grain contactis increased and the tendency for displace-ment of the individual grains isminimized.

Particle ShapeThe shape of individual particles affects the

engineering characteristics of soils. Threeprincipal shapes of soil grains have beenrecognized. They are—

Bulky.Scalelike or platy.Needlelike.

Bulky. Bulky grains are nearly equal in allthree dimensions. This shape characterizessands and gravels and some silts. Bulkygrains may be described by such terms as—

Angular.Subangular.Subrounded.Well-rounded.

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These four subdivisions of the bulky par-ticle shape depend on the amount ofweathering that has occurred (see Figure4-10). These subdivisions are discussed inthe order of desirability for construction.

Angular particles are particles that haverecently been broken up. They are charac-terized by jagged projections, sharp ridges,and flat surfaces. The interlocking charac-teristics of angular gravels and sandsgenerally make them the best materials forconstruction. Such particles are seldomfound in nature because weathering proces-ses normally wear them down in a relativelyshort time. Angular material may beproduced artificially by crushing, but becauseof the time and equipment required for suchan operation, natural materials with othergrain shapes are frequently used.

Subangular particles have been weathereduntil the sharper points and ridges of theiroriginal angular shape have been worn off.The particles are still very irregular in shapewith some flat surfaces and are excellent forconstruction.

Subrounded particles are those on whichweathering has progressed even further.Still somewhat irregular in shape, they haveno sharp corners and few flat areas. Sub-rounded particles are frequently found instream beds. They may be composed of hard,durable particles that are adequate for mostconstruction needs.

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Rounded particles are those in which allprojections have been removed and few ir-regularities in shape remain. The particlesapproach spheres of varying sizes. Roundedparticles are usually found in or near streambeds, beaches, or dunes. Perhaps the mostextensive deposits exist at beaches whererepeated wave action produces almost per-fectly rounded particles that may be uniformin size. Rounded particles also exist in aridenvironments due to wind action and theresulting abrasion between particles. Theyare not desirable for use in asphalt or concreteconstruction until the rounded shape is al-tered by crushing.

Platy. Platy grains are extremely thin com-pared to their length and width. They havethe general shape of a flake of mica or a sheetof paper. Some coarse particles, particularlythose formed by the mechanical breakdown ofmica, are flaky or scalelike in shape. How-ever, most particles that fall in the range ofclay sizes, including the so-called clayminerals, have this characteristic shape. Aswill be explained in more detail later, thepresence of these extremely small platygrains is generally responsible for the plas-ticity of clay. This type of soil is also highlycompressible under static load.

Needlelike. These grains rarely occur.

StructureSoils have a three-phase composition, the

principal ingredients being the soil particles,water, and air. Organic materials are alsofound in the surface layer of most soils. Basicconcepts regarding volume and weightrelationships in a solid mass are shown inFigure 4-11. These relationships form thebasis of soil testing, since they are used inboth quantitative and qualitative reporting ofsoils. It must be recognized that the diagrammerely represents soil mass for studying therelationships of the terms to be discussed. Allvoid and solid volumes cannot be segregatedas shown.

Specific Gravity. The specific gravity,designated by the symbol G, is defined as the

ratio between the weight per unit volume ofthe material at a stated temperature (usually20 degrees Celsius (C)) and the weight perunit volume of water.

Specific gravity =weight of sample in air (grams)_

weight of sample in air (grams) —weight of sample in water (grams)

Test procedures are contained in TM 5-530.The specific gravity of the solid substance ofmost inorganic soils varies between 2.60 and2.80. Tropical iron-rich laterite soils general-ly have a specific gravity of 3.0 or more. Clayscan have values as high as 3.50. Mostminerals, of which the solid matter of soil par-ticles is composed, have a specific gravitygreater than 2.60. Therefore, smaller valuesof specific gravity indicate the possiblepresence of organic matter.

Volume Ratios. The total volume (V) of asoil mass consists of the volume of voids (Vv)and the volume of solids (Vs). The volume ofvoids in turn consists of the volume of air (Va),and the volume of water (Vw) (see Figure4-11). The most important volume ratio is thevoid ratio (e). It is expressed:

Vve = —Vv

The volume of solids is the ratio of the dryweight (Wd) of a soil mass, in pounds, to the

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product of its specific gravity (G) and the unitweight of water (62.4 pounds per cubic foot(pcf). It is expressed:

Wd (lb)Vs

= 62.4 x G

The volume of the water is the ratio of theweight of the water (Ww), in pounds, to theunit weight of the water. It is expressed:

WwVw

= 62.4

The degree of saturation (S) expresses therelative volume of water in the voids and is al-ways expressed as a percentage. It isexpressed:

A soil is saturated if S equals 100 percent,which means all void volume is filled withwater.

Weight Ratios. The total weight (W) of a soilmass consists of the weight of the water (Ww)and the weight of the solids (Ws), the weight ofthe air being negligible. Weight ratios widelyused in soil mechanics are moisture content,unit weight, dry unit weight, and wet unitweight.

Moisture content (w) expressed as a per-centage is the ratio of the weight of the waterto the weight of the solids. It is expressed:

The moisture content may exceed 100 per-cent. By definition, when a soil mass is driedto constant weight in an oven maintained at a.temperature of 105 + 5 degrees C, Ww = 0, andthe soil is said to be oven dry or dry. If a soilmass is cooled in contact with the atmos-phere, it absorbs some water. This waterabsorbed from the atmosphere is calledhydroscopic moisture. TM 5-530 containstesting procedures for determining moisturecontent.

Unit weight (y) is the expression given tothe weight per unit volume of a soil mass. Itis expressed:

In soils terminology, the terms “unit weight”and “density” are used interchangeably.

Wet unit weight (y m), also expressed as wetdensity, is the term used if the moisture con-tent is anything other than zero. The wetunit weight of natural soils varies widely.Depending on denseness and gradation, asandy soil may have a wet unit weight or den-sity of 115 to 135 pcf. Some very dense glacialtills may have wet unit weights as high as 145pcf. Wet unit weights for most clays rangefrom 100 to 125 pcf. Density of soils can begreatly increased by compaction during con-struction. In foundation problems, thedensity of a soil is expressed in terms of wetunit weight.

Dry unit weight (y d), also expressed as drydensity, is the term used if the moisture con-tent is zero. Since no water is present and theweight of air is negligible, it is written:

Dry unit weight normally is used in con-struction problems. The general relationshipbetween wet unit weight and dry unit weightis expressed:

A numerical example of volume-weightrelationships follows:

GIVEN:

A soil mass with:

wet unit weight = 125 pcfmoisture content = 18 percentspecific gravity = 2.65volume = 1 cubic foot (cu ft)

FIND:

y d dry unit weight(2) e, void ratio

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SOLUTION:

Find dry unit weight

Find the void ratio using the formula:e = Vv/Vs

Vs = Wd/62.4 G

Vs = 105.9/62.4 (2.65)

= 0.64 cu ft

Thus, if e = Vv/Vs, substituting computedvalues, then

e = 0.36/0.64= 0.56

The relationships discussed previously areused in calculations involved in soil construc-tion work. They are used along with thenecessary soil tests to classify and to helpdetermine engineering characteristics of soil.

Relative DensityUse of the void ratio is not very effective in

predicting the soil behavior of granular or un-restricted soils. More useful in this respect isthe term relative density, expressed as Dr.Relative density is an index of the degree towhich a soil has been compacted. Valuesrange from O (e = emax) to 1.0 (e = emin). It iswritten:

the natural, in-place, void ratiothe void ratio in the loosestpossible conditionthe void ratio in the most densecondition possible.

The limiting ranges of emax may be foundby pouring the soil loosely into a containerand determining its weight and volume. Thelimiting ranges of emin may be found by tamp-ing and shaking the soil until it reaches aminimum volume and recording its weightand volume at this point. Relative density isimportant for gravels and sands.

Soil-Moisture ConditionsCoarse-grained soils are much less affected

by moisture than are fine-grained soils.Coarser soils have larger void openings andgenerally drain more rapidly. Capillarity isno problem in gravels having only very smallamounts of fines r-nixed with them. Thesesoils will not usually retain large amounts ofwater if they are above the ground watertable. Also, since the particles in sandy andgravelly soils are relatively large (in com-parison to silt and clay particles), they areheavy in comparison to the films of moisturethat might surround them. Conversely, thesmall, sometimes microscopic, particles of afine-grained soil weigh so little that waterwithin the voids has a considerable effect onthem. The following phenomena are ex-amples of this effect:

Clays frequently undergo very largevolume changes with variations inmoisture content. Evidence of this canbe seen in the shrinkage cracks thatdevelop in a lake bed as it dries.Unpaved clay roads, although oftenhard when sunbaked, lose stabilityand turn into mud in a rainstorm.In general, the higher the water con-tent of a clay or silt, the less is itsstrength and hence its bearing capac-ity.

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These effects are very important to an en-gineer and are functions of changing watercontent. The Army’s emphasis on earlyachievement of proper drainage in horizontalconstruction stems from these properties ofcohesive soils.

Adsorbed Water. In general terms, ad-sorbed water is water that may be present asthin films surrounding the separate soil par-ticles. When the soil is in an air-drycondition, the adsorbed water present iscalled hydroscopic moisture. Adsorbed wateris present because the soil particles carry anegative electrical charge. Water is dipolar;it is attracted to the surface of the particle andbound to it (see Figure 4-12). The water filmsare affected by the chemical and physicalstructure of the soil particle and its relativesurface area. The relative surface area of aparticle of fine-grained soil, particularly if ithas a flaky or needlelike shape, is muchgreater than for coarse soils composed ofbulky grains. The electrical forces that bindadsorbed water to the soil particle also aremuch greater. Close to the particle, the watercontained in the adsorbed layer has proper-ties quite different from ordinary water. Inthe portion of the layer immediately adjacentto the particle, the water may behave as asolid, while only slightly farther away it be-haves as a viscous liquid. The total thicknessof the adsorbed layer is very small, perhaps onthe order of 0.00005 mm for clay soils. Incoarse soils, the adsorbed layer is quite thincompared with the thickness of the soil par-ticle. This, coupled with the fact that thecontact area between adjacent grains is quitesmall, leads to the conclusion that thepresence of the adsorbed water has little ef-fect on the physical properties ofcoarse-grained soils. By contrast, for finersoils and particularly in clays, the adsorbedwater film is thick in comparison with par-ticle size. The effect is very pronounced whenthe particles are of colloidal size.

Plasticity and Cohesion. Two importantaspects of the engineering behavior of fine-grained soils are directly associated with the

existence of adsorbed water films. Theseaspects are plasticity and cohesion.

Plasticity is the ability of a soil to deformwithout cracking or breaking. Soils in whichthe adsorbed films are relatively thick com-pared to particle size (such as clays) areplastic over a wide range of moisture con-tents. This is presumably because theparticles themselves are not in direct contactwith one another. Plastic deformation cantake place because of distortion or shearing ofthe outside layer of viscous liquid in the mois-ture films. Coarse soils (such as clean sandsand gravels) are nonplastic. Silts also are es-sentially nonplastic materials, since they areusually composed predominantly of bulkygrains; if platy grains are present, they maybe slightly plastic.

A plasticity index (PI) is used to determineif soils are cohesive. Not all plastic soils arecohesive; soil is considered cohesive if its PIis 5. That is, they possess some cohesion orresistance to deformation because of the sur-face tension present in the water films. Thus,wet clays can be molded into various shapeswithout breaking and will retain theseshapes. Gravels, sands, and most silts are notcohesive and are called cohesionless soils.Soils of this general class cannot be moldedinto permanent shape and have little or nostrength when dry and unconfined. Some ofthese soils may be slightly cohesive whendamp. This is attributed to what is some-times called apparent cohesion, which is also

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due to the surface tension in the water filmsbetween the grains.

Clay Minerals and Base Exchange. Thevery fine (colloidal) particles of clay soils con-sist of clay minerals, which are crystalline instructure. These minerals are complex com-pounds of hydrous aluminum silicates andare important because their presence greatlyinfluences a soil’s physical properties. X rayshave been used to identify several differentkinds of clay minerals that have somewhatdifferent properties. Two extreme types arekaolinite and montmorillonite. Both havelaminated crystalline structures, but they be-have differently. Kaolinite has a very rigidcrystalline structure, while montmorillonitecan swell by taking water directly into its lat-tice structure. Later, the flakes themselvesmay decrease in thickness as the water issqueezed out during drying, the flakes arethus subject to detrimental shrinkage and ex-pansion. An example of this type of materialis bentonite, largely made up of themontmorillonite type of clay mineral. Be-cause of its swelling characteristics,bentonite is widely used commercially in theconstruction of slurry walls and temporarydam cores. Most montmorillonites havemuch thicker films of adsorbed water than dokaolinites. Kaolinites tend to shrink andswell much less than montmorillonites withchanges in moisture content. In addition, theadsorbed water film may contain disas-sociated ions. For example, metallic cations,such as sodium, calcium, or magnesium, maybe present. The presence of these cations alsoaffects the physical behavior of the soil. Amontmorillonite clay, for example, in whichcalcium cations predominate in the adsorbedlayer may have properties quite differentfrom a similar clay in which sodium cationspredominate. The process of replacing ca-tions of one type with cations of another typein the surface of the adsorbed layer is calledbase (or cation) exchange. It is possible to ef-fect this replacement and thereby alter thephysical properties of a clay soil. For ex-ample, the soil may swell, the plasticity maybe reduced, or the permeability may be in-creased by this general process.

Capillary Phenomena. Capillary phenom-ena in soils are important for two reasons.First, water moves by capillary action into a

soil from a free-water surface. This aspect ofcapillary phenomena is not discussed herebut is covered in Chapter 8. Second, capillaryphenomena are closely associated with theshrinkage and expansion (swelling) of soils.

The capillary rise of water in small tubes is acommon phenomenon, which is caused bysurface tension (see Figure 4-13). The waterthat rises upward in a small tube is in tension,hanging on the curved boundary between airand water (meniscus) as if from a suspendingcable. The tensile force in the meniscus isbalanced by a compressive force in the walls ofthe tube. Capillary phenomena in smalltubes can be simply analyzed and equationsderived for the radius of the curved meniscus,the capillary stress (force per unit of area),and the height of capillary rise (see hc in Fig-ure 4-13). A soil mass may be regarded asbeing made up of a bundle of small tubesformed by the interconnected void spaces.These spaces form extremely irregular, tor-tuous paths for the capillary movement ofwater. An understanding of capillary actionin soils is thus gained by analogy. Theoreticalanalyses indicate that maximum possiblecompressive pressure that can be exerted bycapillary forces is inversely proportional tothe size of the capillary openings.

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Shrinkage. Many soils undergo a very con-siderable reduction in volume when theirmoisture content is reduced. The effect ismost pronounced when the moisture contentis reduced from that corresponding to com-plete saturation to a very dry condition. Thisreduction in volume is called shrinkage and isgreatest in clays. Some of these soils show areduction in volume of 50 percent or morewhile passing from a saturated to an oven-drycondition. Sands and gravels, in general,show very little or no change in volume withchange in moisture content. An exception tothis is the bulking of sands, which is dis-cussed below. The shrinkage of a clay massmay be attributed to the surface tension exist-ing in the water films created during thedrying process. When the soil is saturated, afree-water surface exists on the outside of thesoil mass, and the effects of surface tensionare not important. As the soil dries out be-cause of evaporation, the surface waterdisappears and innumerable meniscuses arecreated in the voids adjacent to the surface ofthe soil mass. Tensile forces are created ineach of these boundaries between water andair. These forces are accompanied by com-pressive forces that, in a soil mass, act on thesoil structure. For the typical, fairly densestructure of a sand or gravel, the compressiveforces are of little consequence; very little orno shrinkage results. In fine-grained soils,the soil structure is compressible and themass shrinks. As drying continues, the massattains a certain limiting volume. At thispoint, the soil is still saturated. The moisturecontent at this stage is called the shrinkagelimit. Further drying will not cause a reduc-tion in volume but may cause cracking as themeniscuses retreat into the voids. In claysoils, the internal forces created duringdrying may become very large. The existenceof these forces also principally accounts forthe rocklike strength of a dried clay mass.Both silt and clay soils may be subject todetrimental shrinkage with disastrousresults in some practical situations. For ex-ample, the uneven shrinkage of a clay soilmay deprive a concrete pavement of theuniform support for which it is designed;severe cracking or failure may result whenwheel loads are applied to the pavement.

Swelling and Slaking. If water is againmade available to a still-saturated clay soilmass that has undergone shrinkage, waterenters the soil’s voids from the outside andreduces or destroys the internal forces pre-viously described. Thus, a clay mass willabsorb water and expand or swell. If expan-sion is restricted, as by the weight of aconcrete pavement, the expansion force maybe sufficient to cause severe pavement crack-ing. If water is made available to the soil afterit has dried below the shrinkage limit, themass generally disintegrates or slakes. Slak-ing may be observed by putting a piece of dryclay into a glass of water. The mass will fallcompletely apart, usually in a matter ofminutes. Construction problems associatedwith shrinkage and expansion are generallysolved by removing the soils that are subjectto these phenomena or by taking steps toprevent excessive changes in moisture con-tent.

Bulking of Sands. Bulking is a phe-nomenon that occurs in dry or nearly dry sandwhen a slight amount of moisture is intro-duced into the soil and the soil is disturbed.Low moisture contents cause increased sur-face tension, which pulls the grains togetherand inhibits compaction. As a result, slightlymoist sands can have lower compacted den-sities than totally dry or saturated sands.Commonly in sands, this problem is madeworse because a slight addition of moistureabove the totally dry state increases the slid-ing coefficient of the particles. The U-shapedcompaction curve, with characteristic free-draining soils (sands and gravels), illustratesthe concept of bulking. Adding sufficientwater to saturate the sand eliminates surfacetension, and the sand can be compacted to itsdensest configuration (see Figure 4-14, page4-18).

CONSISTENCY (ATTERBERG) LIMITSA fine-grained soil can exist in any one of

several different states, depending on theamount of water in the soil. The boundariesbetween these different soil states are mois-ture contents called consistency limits. Theyare also called Atterberg limits after theSwedish soil scientist who first defined themin 1908. The shrinkage limit is the boundary

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between the semisolid and solid states. Theplastic limit (PL) is the boundary between thesemisolid and plastic states. The liquid limit(LL) is the boundary between the plastic andliquid states. Above the LL, the soil ispresumed to behave as a liquid. The numeri-cal difference between the LL and the PL iscalled the PI and is the range of moisture con-tent over which the soil is in a plasticcondition. The Atterberg limits are impor-tant index properties of fine-grained soils.They are particularly important in classifica-tion and identification. They are also widelyused in specifications to control the proper-ties, compaction, and behavior of soilmixtures.

Test ProceduresThe limits are defined by more or less ar-

bitrary and standardized test procedures thatare performed on the portion of the soil thatpasses the Number 40 sieve. This portion ofsoil is sometimes called the soil binder.TM 5-530 contains detailed test procedures tobe used in determining the LL and the PL.The tests are performed with the soil in a dis-turbed condition.

Liquid Limit. The LL (or wL ) is defined asthe minimum moisture content at which a soilwill flow upon application of a very smallshearing force. With only a small amount ofenergy input, the soil will flow under its ownweight. In the laboratory, the LL is usuallydetermined by use of a mechanical device (seeFigure 4-15). The detailed testing procedureis described in TM 5-530.

Plastic Limit. The PL (or wp) is arbitrarilydefined as the lowest moisture content atwhich a soil can be rolled into a thread 1/8inch in diameter without crushing or break-ing. If a cohesive soil has a moisture contentabove the PL, a thread may be rolled to lessthan 1/8 inch in diameter without breaking.If the moisture content is below the PL, thesoil will crumble when attempts are made toroll it into 1/8-inch threads. When the mois-ture content is equal to the PL, a thread canbe rolled out by hand to 1/8 inch in diameter;then it will crumble or break into pieces 1/8 to3/8 inch long when further rolling is at-tempted. Some soils (for example, cleansands) are nonplastic and the PL cannot bedetermined. A clean sand or gravel willprogress immediately from the semisolid tothe liquid state.

Plasticity IndexThe PI (or Ip) of a soil is the numerical dif-

ference between the LL and the PL. Forexample, if a soil has a LL of 57 and a PL of 23,then the PI equals 34 (PI = LL - PL). Sandysoils and silts have characteristically low PIs,while most clays have higher values. Soils thathave high PI values are highly plastic and aregenerally highly compressible and highly

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cohesive. The PI is inversely proportional to Casagrande of Harvard University and ledthe permeability of a soil. Soils that do not to the development of the plasticity chart.have a PL, such as clean sands, are reported The chart’s development and use in class-as having a PI of zero. ifying and identifying soils and selecting the

best of the available soils for a particular con-Relationships between the LLs and PIs struction application are discussed in

of many soils were studied by Arthur Chapter 5.

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CHAPTER 5

S o i l C l a s s i f i c a t i o n

Early attempts to classify soils were basedprimarily on grain size. These are the tex-tural classification systems. In 1908, asystem that recognized other factors wasdeveloped by Atterberg in Sweden andprimarily used for agricultural purposes.Somewhat later, a similar system wasdeveloped and used by the Swedish Geotech-nical Commission. In the United States, theBureau of Public Roads System wasdeveloped in the late twenties and was inwidespread use by highway agencies by themiddle thirties. This system has been revisedover time and is widely used today. The Air-fieid Classification System was developed byProfessor Arthur Casagrande of HarvardUniversity during World War II. A modifica-tion of this system, the USCS, was adopted bythe US Army Corps of Engineers and theBureau of Reclamation in January 1952. Anumber of other soil classification systemsare in use throughout the world, and themilitary engineer should be familiar with themost common ones.

The principal objective of any soil classifica-tion system is predicting the engineeringproperties and behavior of a soil based on afew simple laboratory or field tests.Laboratory and/or field test results are thenused to identify the soil and put it into a groupthat has soils with similar engineering char-acteristics. Probably no existing classifi-cation system completely achieves the statedobjective of classifying soils by engineeringbehavior because of the number of variables

involved in soil behavior and the variety ofsoil problems encountered. Considerableprogress has been made toward this goal, par-ticularly in relationship to soil problemsencountered in highway and airport en-gineering. Soil classification should not beregarded as an end in itself but as a toolto further your knowledge of soil behavior.

Section I. Unified SoilClassification System

SOIL CATEGORIESSoils seldom exist in nature separately as

sand, gravel, or any other single component.Usually they occur as mixtures with varyingproportions of particles of different sizes.Each component contributes its charac-teristics to the mixture. The USCS is basedon the characteristics of the soil that indicatehow it will behave as a construction material.

In the USCS, all soils are placed into one ofthree major categories. They are—

Coarse-grained.Fine-grained.Highly organic.

The USCS further divides soils that havebeen classified into the major soil categoriesby letter symbols, such as—

S for sand.G for gravel.M for silt.C for clay.

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A soil that meets the criteria for a sandyclay would be designated (SC). There arecases of borderline soils that cannot be clas-sified by a single dual symbol, such as GM forsilty gravel. These soils may require four let-ters to fully describe them. For example,(SM-SC) describes a sand that contains ap-preciable amounts of silt and clay.

Coarse-Grained SoilsCoarse-grained soils are defined as those in

which at least half the material is retained ona Number 200 sieve. They are divided intotwo major divisions, which are—

Gravels.Sands.

A coarse-grained soil is classed as gravel ifmore than half the coarse fraction by weightis retained on a Number 4 sieve. The symbolG is used to denote a gravel and the symbol Sto denote a sand. No clearcut boundary existsbetween gravelly and sandy soils; as far assoil behavior is concerned, the exact point ofdivision is relatively unimportant. Where amixture occurs, the primary name is thepredominant fraction and the minor fractionis used as an adjective. For example, a sandygravel would be a mixture containing moregravel than sand by weight. Additionally,gravels are further separated into eithercoarse gravel or fine gravel with the 3/4-inchsieve as the dividing line and sands are eithercoarse, medium, or fine with the Number 10and Number 40 sieves, respectively. Thecoarse- grained soils may also be furtherdivided into three groups on the basis of theamount of fines (materials passing a Number200 sieve) they contain. These amounts are—

Less than 5 percent.More than 12 percent.Between 5 and 12 percent.

Coarse-grained soils with less than 5 per-cent passing the Number 200 sieve may fallinto the following groups:

(GW is well-graded gravels and gravel-sand mixtures with little or no fines.The presence of the fines must not not-ably change the strength characteristics

of the coarse-grained fraction andmust not interfere with its free-draining characteristics.(SW) is well-graded sands and grav-elly sands with little or no fines. Thegrain-size distribution curves for (GW)and (SW) in Figure 4-9, page 4-11, aretypical of soils included in thesegroups. Definite laboratory classifica-tion criteria have been established tojudge if the soil is well-graded (seeChapter 4). For the (GW) group, theCu must be greater than 4; for the(SW) group, greater than 6. For bothgroups, the CC must be between 1 and3.(GP) is poorly graded gravels andsandy gravel mixtures with little orno fines.(SF) is poorly graded sands andgravelly sands with little or no fines.These soils do not meet the gradationrequirements established for the (GW)and (SW) groups. The grain-size dis-tribution curve marked (GP) in Fig-ure 4-9, page 4-11, is typical of apoorly graded gravel-sand mixture,while the curve marked (SP) is apoorly graded (uniform) sand.

Coarse-grained soils containing more than12 percent passing the Number 200 sieve fallinto the following groups:

(GM) is silty gravel and poorly gradedgravel/sand-silt mixtures.(SM) is silty sands and poorly gradedsand-silt mixtures.

Gradation of these materials is not con-sidered significant. For both of these groups,the Atterberg limits must plot below the A-line of the plasticity chart shown in Figure5-1. A dual symbol system allows moreprecise classification of soils based on grada-tion and Atterberg limits.

(GC) is clayey gravels and poorlygraded gravel-sand-clay mixtures.(SC) is clayey sands and poorlygraded sand-clay mixtures.

Soil Classification 5-2

FM 5-410

Gradation of these materials is not con-sidered significant. For both of these groups,the Atterberg limits plot above the A-line.

The use of the symbols M and C is based onthe plasticity characteristics of the materialpassing the Number 40 sieve. The LL and PIare used in determining the plasticity of thefine materials. If the plasticity chart shownin Figure 5-1 is analyzed with the LL and PI,it is possible to determine if the fines areclayey or silty. The symbol M is used to indi-cate that the material passing the Number 40sieve is silty in character. M usually desig-nates a fine-grained soil of little or noplasticity. The symbol C is used to indicatethat the binder soil is clayey in character. A

dual symbol system allows more precise clas-sification of soils based on gradation andAtterberg limits.

For example, coarse-grained soils with be-tween 5 and 12 percent of material passingthe Number 200 sieve, and which meet thecriteria for well-graded soil, require a dualsymbol, such as—

(GW-GM)(GP-GM)(GW-GC)(GP-GC)(SW-SC}(SW-SM)(SP-SC)(SP-SM)

Soil Classification 5-3

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Similarly, coarse-grained soils containingmore than 12 percent of material passing theNumber 200 sieve, and for which the limitsplot in the hatched portion of the plasticitychart (see Figure 5-1, page 5-3), are borderlinebetween silt and clay and are classified as(SM-SC) or (GM-GC).

In rare instances, a soil may fall into morethan one borderline zone. If appropriate sym-bols were used for each possible classification,the result would be a multiple designationusing three or more symbols. This approachis unnecessarily complicated. It is consideredbest to use only a double symbol in thesecases, selecting the two believed most repre-sentative of probable soil behavior. If there isdoubt, the symbols representing the poorer ofthe possible groupings should be used. Forexample, a well-graded sandy soil with 8 per-cent passing the Number 200 sieve, with anLL of 28 and a PI of 9, would be designated as(SW-SC). If the Atterberg limits of this soilwere such as to plot in the hatched portion ofthe plasticity chart (for example, an LL of 20and a PI of 5), the soil could be designatedeither (SW-SC) or (SW-SM), depending on thejudgment of the soils technician.

Fine-Grained SoilsFine-g-rained soils are those in which more

than half the material passes a Number 200sieve. The fine-grained soils are not classifiedby grain size but according to plasticity andcompressibility. Laboratory classificationcriteria are based on the relationship betweenthe LL and the PI, determined from the plas-ticity chart shown in Figure 5-1, page 5-3.The chart indicates two major groupings offine-g-rained soils. These are—

The L groups, which have LLs <50.The H groups, which have LLs of50.

The symbols L and H represent low andhigh compressibility, respectively. Fine-grained soils are further divided based ontheir position above or below the A-line of theplasticity chart.

Typical soils of the (ML) and (MH) groupsare inorganic silts. Those of low plasticity are

Soil Classification 5-4

in the (ML) group; others are in the (MH)group. Atterberg limits of these soils all plotbelow the A-line. The (ML) group includes-

Very fine sands.Rock flours.Silty or clayey fine sands with slightplasticity.

Micaceous and diatom aceous soils gen-erally fall into the (MH) group but may extendinto the (ML) group with LLs<50. The samestatement is true of certain types of kaolinclays, which have low plasticity. Plastic siltsfall into the (MH) group.

In (CL) and (CH) groups, the C stands forclay, with L and H denoting low or high com-pressibility. These soils plot above the A-lineand are principally inorganic clays. The (CL)group includes gravelly clays, sandy clays,silty clays, and lean clays. In the (CH) groupare inorganic clays of high plasticity, includ-ing fat clays, the gumbo clays of the southernUnited States, volcanic clays, and bentonite.The glacial clays of the northern UnitedStates cover a wide band in the (CL) and (CH)groups.

Soils in the (OL) and (OH) groups are char-acterized by the presence of organic matter,hence the symbol O. The Atterberg limits ofthese soils generally plot below the A-line.Organic silts and organic silt clays of lowplasticity fall into the (OL) group, while or-ganic clays plot in the (OH) zone of theplasticity chart. Many organic silts, silt-clays,and clays deposited by rivers along the lowerreaches of the Atlantic seaboard have LLs be-tween 40 and 100 and plot below the A-line.Peaty soils may have LLs of several hundredpercent and their Atterberg limits generallyplot below the A-line.

Fine-grained soils having limits that plot inthe shaded portion of the plasticity chart aregiven dual symbols (for example, (CL-ML)).Several soil types exhibiting low plasticityplot in this general region on the chart and nodefinite boundary between silty and clayeysoils exists.

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Highly Organic SoilsA special classification, (Pt), is reserved for

the highly organic soils, such as peat, whichhave many undesirable engineering charac-teristics. No laboratory criteria areestablished for these soils, as they generallycan be easily identified in the field by theirdistinctive color and odor, spongy feel, andfrequently fibrous texture. Particles ofleaves, grass, branches, or other fibrousvegetable matter are common components ofthese soils.

Table 5-1, page 5-7, and Table 5-2, page 5-9,are major charts which present informationapplicable to the USCS and procedures to befollowed in identifying and classifying soilsunder this system. Principal categoriesshown in the chart include—

Soil groups, soil group symbols, andtypical soil names.Laboratory classification criteria.Field identification procedures.Information for describing soils.

These charts are valuable aids in soil clas-sification problems. They provide a simplesystematic means of soil classification.

LABORATORY TESTINGUsually soil samples are obtained during

the soil survey and are tested in thelaboratory to determine test properties forclassifying the soils. The principal tests are—

Mechanical analysis.Liquid limit.Plastic limit.

These tests are used for all soils exceptthose in the (Pt) group. With the percentagesof gravel, sand, and fines and the LL and PI,the group symbol can be obtained from thechart in Table 5-2, page 5-9, by reading thediagram from top to bottom. For the gravelsand sands containing 5 percent (or less) fines,the shape of the grain-size distribution curvecan be used to establish whether the materialis well-graded or poorly graded. For the

fine-grained soils, it is necessary to plot theLL and PI in the drawing on Figure 5-1, page5-3, to establish the proper symbol. Organicsilts or clays (ML) and (MH) are subjected toLL and PL tests before and after oven drying.An organic silt or clay shows a radical drop inthese limits as a result of oven drying. An in-organic soil shows a slight drop that is notsignificant. Where there is an appreciabledrop, the predrying values should be usedwhen the classification is determined fromTable 5-2, page 5-9.

DESIRABLE SOIL PROPERTIESFOR ROADS AND AIRFIELDS

The properties desired in soils for founda-tions under roads and airfields are—

Adequate strength.Resistance to frost action (in areaswhere frost is a factor).Acceptable compression and expan-sion.Adequate drainage.Good compaction.

Some of these properties may be suppliedby proper construction methods. For in-stance, materials having good drainagecharacteristics are desirable, but if suchmaterials are not available locally, adequatedrainage may be obtained by installing aproperly designed water-collecting system.Strength requirements for base coursematerials are high, and only good qualitymaterials are acceptable. However, lowstrengths in subgrade materials may be com-pensated for in many cases by increasing thethickness of overlying base materials or usinga geotextile (see Chapter 11). Proper designof road and airfield pavements requires theevaluation of soil properties in more detailthan possible by use of the general soils clas-sification system. However, the grouping ofsoils in the classification system gives an ini-tial indication of their behavior in road andairfield construction, which is useful in site orroute selection and borrow source reconnais-sance.

Soil Classification 5-5

FM 5-410

General characteristics of the soil groupspertinent to roads and airfields are in the soilclassification sheet in Table 5-3, page 5-11, asfollows:

Columns 1 through 5 show major soildivisions, group symbols, hatching,and color symbols.Column 6 gives names of soil types.Column 7 evaluates the performance(strength) of the soil groups whenused as subgrade materials that arenot subject to frost action.Columns 8 and 9 make a similarevaluation for the soils when used assubbase and base materials.Column 10 shows potential frost ac-tion.Column 11 shows compressibility andexpansion characteristics.Column 12 presents drainage charac-teristics.Column 13 shows types of compactionequipment that perform satisfactorilyon the various soil groups.Column 14 shows ranges of unit dryweight for compacted soils.Column 15 shows ranges of typicalCalifornia Bearing Ratio (CBR) val-ues to be anticipated for use in air-field design.Column 16 gives ranges of modulus ofsubgrade reaction, k.

The various features are discussed in thefollowing paragraphs.

StrengthIn column 3 of Table 5-3, page 5-11, the

basic soil groups (GM) and (SM) have eachbeen subdivided into two groups designatedby the following suffixes:

d (represents desirable base and sub-base materials).u (represents undesirable base andsubbase materials).

This subdivision applies to roads and air-fields only and is based on field observationand laboratory tests on soil behavior in thesegroups. The basis for the subdivision is theLL and PI of the fraction of the soil passing

Soil Classification 5-6

the Number 40 sieve. The suffix d is usedwhen the LL is 25 and the PI is fix u is used otherwise.

The descriptions in columns 7, 8, and 9generally indicate the suitability of the soilgroups for use as subgrade, subbase, or basematerials not subjected to frost action. Inareas where frost heaving is a problem, thevalue of materials as subgrades is reduced,depending on the potential frost action of thematerial (see column 10). Proper design pro-cedures should be used in situations wherefrost action is a problem.

Coarse-Grained Soils. Generally, thecoarse-grained soils make the best subgrade,subbase, and base materials. The (GW)group has excellent qualities as a basematerial. The adjective “excellent” is notused for any of these soils for base courses, be-cause “excellent” should only be used todescribe a high quality processed crushedstone. Poorly graded gravels and some siltygravels (groups (GP) and (GMd)) are usuallyonly slightly less desirable as subgrade orsubbase materials. Under favorable condi-tions, these gravels may be used as basematerials; however, poor gradation and otherfactors sometimes reduce the value of thesesoils so they offer only moderate strength.For example—

The (GMu), (GC), and (SW) groupsare reasonably good subgrade orselect materials but are generallypoor to not suitable as base materials.

The (SP) and (SMd) soils usually areconsidered fair to good subgrade andsubbase materials but are generailypoor to not suitable as base materials.

Fine-Grained Soils. The fine-grained soilsrange from fair to very poor subgradematerials as follows—

Silts and lean clays (ML) and (CL)are fair to poor.

Organic silts, lean organic clays, andmicaceous or diatom aceous soils (OL)and (MH) are poor.

Fat clays and fat organic clays (CH)and (OH) are poor to very poor.

5; the sur-

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Soil Classification 5-8

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Soil Classification 5-10

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Soil Classification 5-12

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These qualities are compensated for inflexible pavement design by increasing thethickness of overlying base material. In rigidpavement design, these qualifications arecompensated for by increasing the pavementthickness or by adding a base course layer.None of the fine-grained soils are suitable asa subbase under bituminous pavements, butsoils in the (ML) and (CL) groups may be usedas select material. The fibrous organic soils(group (Pt)) are very poor subgrade materialsand should be removed wherever possible;otherwise, special construction measuresshould be adopted. They are not suitable assubbase and base materials. The CBR valuesshown in column 15 give a relative indicationof the strength of the various soil groups whenused in flexible pavement design. Similarly,values of subgrade modulus (k) in column 16are relative indications of strengths fromplate-bearing tests when used in rigid pave-ment design. Actual test values should beused for this purpose instead of the ap-proximate values shown in the tabulation.

For wearing surfaces on unsurfaced roads,slightly plastic sand-clay-gravel mixtures(GC) are generally considered the most satis-factory. However, they should not contain toolarge a percentage of fines, and the PI shouldbe in the range of 5 to about 15.

Frost ActionThe relative effects of frost action on the

various soil groups are shown in column 10.Regardless of the frost susceptibility of thevarious soil groups, two conditions must bepresent simultaneously before frost action isa major consideration. These are-

A source of water during the freezingperiod.A sufficient period for the freezingtemperature to penetrate the ground.

Water necessary for the formation of icelenses may become available from a highgroundwater table, a capillary supply, waterheld within the soil voids, or through infiltra-tion. The degree of ice formation that willoccur is markedly influenced by physical fac-tors, such as—

Topographic position.

Stratification of the parent soil,Transitions into a cut section.Lateral flow of water from side cuts.Localized pockets of perched ground-water,Drainage conditions.

In general, the silts and fine silty sands aremost susceptible to frost. Coarse-grainedmaterials with little or no fines are affectedonly slightly or not at all. Clays ((CL) and(CH)) are subject to frost action, but the loss ofstrength of such materials may not be asgreat as for silty soils. Inorganic soils con-taining less than 3 percent (by weight) ofgrains finer than 0.02 mm in diameter areconsidered non frost-susceptible. Wherefrost-susceptible soils occur in subgrades andfrost is a problem, two acceptable methods ofpavement design are available:

Place a sufficient depth of acceptablegranular material over the soils tolimit the depth of freezing in the sub-grade and thereby prevent the det-rimental effects of frost action.Use a design load capacity during theperiod of the year when freezing con-ditions are expected.

In the second case, design is based on thereduced strength of the subgrade during thefrost-melting period. Often an appropriatedrainage measure to prevent the accumula-tion of water in the soil pores helps limit icedevelopment in the subgrade and subbase.

CompressionThe compression or consolidation of soils

becomes a design factor primarily whenheavy fills are made on compressible soils.The two types of compression are—

Relatively long-term compression orconsolidation under the dead weightof the structure.Short-term compression and reboundunder moving wheel loads.

If adequate provision is made for this typeof settlement during construction, it will havelittle influence on the load-carrying capacity

Soil Classification 5-13

FM 5-410

of the pavement. However, when elastic soilssubject to compression and rebound underwheel loads are encountered, adequateprotection must be provided. Even smallmovements of this type soil may be detrimen-tal to the base and wearing course ofpavements. Fortunately, the free-draining,coarse-grained soils ((GW), (GP), (SW), and(SP)), which generally make the best sub-grade and subbase materials, exhibit almostno tendency toward high compressibility orexpansion. In general, the compressibility ofsoil increases with an increasing LL. How-ever, compressibility is also influenced by soilstructure, grain shape, previous loading his-tory, and other factors not evaluated in theclassification system. Undesirable compres-sion or expansion characteristics may bereduced by distributing the load through agreater thickness of overlying material.These factors are adequately handled by theCBR method of design for flexible pavements.However, rigid pavements may require theaddition of an acceptable base course underthe pavement.

DrainageThe drainage characteristics of soils are a

direct reflection of their permeability. Theevaluation of drainage characteristics for usein roads and runways is shown in column 12of Table 5-3, page 5-11. The presence of waterin base, subbase, and subgrade materials, ex-cept for free-draining, coarse-grained soils,may cause pore water pressures to developresulting in a loss of strength. The water maycome from infiltration of groundwater or rain-water or by capillary rise from an underlyingwater table. While free-draining materialspermit rapid draining of water, they also per-mit rapid ingress of water. If free-drainingmaterials are adjacent to less perviousmaterials and become inundated with water,they may serve as reservoirs. Adjacent,poorly drained soils may become saturated.The gravelly and sandy soils with little or nofines (groups (GW), (GP), (SW), (SP)) have ex-cellent drainage characteristics. The (GMd)and (SMd) groups have fair to poor drain-age characteristics, whereas the (GMu),(GC), (SMu), and (SC) groups have verypoor drainage characteristics or are practi-cally impervious. Soils of the (ML), (MH),and (Pt) groups have fair to poor drainage

characteristics. All other groups have poordrainage characteristics or are practically im-pervious.

CompactionCompacting soils for roads and airfields re-

quires attaining a high degree of densityduring construction to prevent detrimentalconsolidation from occurring under anembankment’s weight or under traffic. In ad-dition, compaction reduces the detrimentaleffects of water. Processed materials, such ascrushed rock, are often used as a base courseand require special treatment during com-paction. Types of compaction equipment thatmay be used to achieve the desired soil den-sities are shown in Table 5-3, column 13, page5-11. For some of the soil groups, severaltypes of equipment are listed because varia-tions in soil type within a group may requirethe use of a specific type of compaction equip-ment. On some construction projects, morethan one type of compaction equipment maybe necessary to produce the desired densities.For example, recommendations include—

Steel-wheeled rollers for angularmaterials with limited amounts offines.Crawler-type tractor or rubber-tiredrollers for gravels and sand.Sheepsfoot rollers for coarse-grainedor fine-grained soils having somecohesive qualities.Rubber-tired rollers for final compac-tion operations for most soil exceptthose with a high LL (group H).

Suggested minimum weights of the varioustypes of equipment are shown in note 2 ofTable 5-3, page 5-11. Column 14 shows rangesof unit dry weight for soil compacted accord-ing to the moisture-density testingprocedures outlined in Military Standard621A, method 100. These values are includedprimarily for guidance; base design or controlof construction should be based on laboratorytest results.

DESIRABLE SOIL PROPERTIES FOREMBANKMENTS AND FOUNDATIONS

Table 5-4 lists the soil characteristics per-tinent to embankment and foundation

Soil Classification 5-14

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Soil Classification 5-16

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construction. After the soil has been clas-sified, look at column 3 and follow itdownward to the soil class. Table 5-4, page5-15, contains the same type of information asTable 5-3, page 5-11, except that column 8lists the soil permeability and column 12 listspossible measures to control seepage.Material not pertinent to embankments andfoundations, such as probable CBR values,are not contained in Table 5-4, page 5-15.Both tables are used in the same manner.Read the notes at the bottom of both tablescarefully.

SOIL GRAPHICSIt is customary to present the results of

soils explorations on drawings as schematicrepresentations of the borings or test pits oron soil profiles with the various soils en-countered shown by appropriate symbols.One approach is to write the group letter sym-bol in the appropriate section of the log. As analternative, hatching symbols shown incolumn 4 of Table 5-3, page 5-11, may beused. In addition, show the natural watercontent of fine-grained soils along the side ofthe log. Use other descriptive remarks as ap-propriate. Colors may be used to delineatesoil types on maps and drawings. A sug-gested color scheme to show the major soilgroups is described in column 5. Boring logsare discussed in more detail in Chapter 3.Soil graphics generated in terrain studiesusually use numeric symbols, each of whichrepresents a USCS soil type.

FIELD IDENTIFICATIONThe soil types of an area are an important

factor in selecting the exact location of air-fields and roads. The military engineer,construction foreman, and members of en-gineer reconnaissance parties must be able toidentify soils in the field so that the engineer-ing characteristics of the various soil typesencountered can be compared. Because of theneed to be economical in time, personnel,equipment, materiel, and money, selection ofthe project site must be made with these fac-tors in mind. Lack of time and facilities oftenmake laboratory soil testing impossiblein military construction. Even where

laboratory tests are to follow, field identifica-tion tests must be made during the soilexploration to distinguish between the dif-ferent soil types encountered so thatduplication of samples for laboratory testingis minimized. Several simple field identifica-tion tests are described in this manual. Eachtest may be performed with a minimum oftime and equipment, although seldom will allof them be required to identify a given soil.The number of tests required depends on thetype of soil and the experience of the in-dividual performing them. By using thesetests, soil properties can be estimated andmaterials can be classified. Such classifica-tions are approximations and should not beused for designing permanent or semiper-manent construction.

ProceduresThe best way to learn field identification is

under the guidance of an experienced soilstechnician. To learn without such assistance,systematically compare laboratory testresults for typical soils in each group with the“feel” of these soils at various moisture con-tents.

An approximate identification of a coarse-grained soil can be made by spreading a drysample on a flat surface and examining it,noting particularly grain size, gradation,grain shape, and particle hardness. Alllumps in the sample must be thoroughly pul-verized to expose individual grains and toobtain a uniform mixture when water isadded to the fine-grained portion. A rubber-faced or wooden pestle and a mixing bowl isrecommended for pulverizing. Lumps mayalso be pulverized by placing a portion of thesample on a firm, smooth surface and usingthe foot to mash it. If an iron pestle is used forpulverizing, it will breakup the mineralgrains and change the character of the soil;therefore, using an iron pestle is discouraged.

Tests for identification of the fine-g-rainedportion of any soil are performed on the por-tion of the material that passes a Number 40sieve. This is the same soil fraction used inthe laboratory for Atterberg limits tests, such

FM 5-410

as plasticity. If this sieve is not available, arough separation may be made by spreadingthe material on a flat surface and removingthe gravel and larger sand particles. Fine-grained soils are examined primarily forcharacteristics related to plasticity.

EquipmentPractically all the tests to be described may

be performed with no equipment or acces-sories other than a small amount of water.However, the accuracy and uniformity ofresults is greatly increased by the proper useof certain equipment. The following equip-ment is available in nearly all engineer units(or may be improvised) and is easilytransported:

A Number 40 US standard sieve.Any screen with about 40 openingsper lineal inch could be used, or anapproximate separation may be usedby sorting the materials by hand.Number 4 and Number 200 sieves areuseful for separating gravels, sands,and fines.A pick and shovel or a set ofentrenching tools for obtaining sam-ples. A hand earth auger is useful ifsamples are desired from depths morethan a few feet below the surface.A spoon issued as part of a messequipment for obtaining samples andfor mixing materials with water todesired consistency.A bayonet or pocket knife for obtain-ing samples and trimming them tothe desired size.A small mixing bowl with a rubber-faced or wooden pestle for pulverizingthe fine-grained portion of the soil.Both may be improvised by using acanteen cup and a wooden dowel.Several sheets of heavy nonabsorbentpaper for rolling samples.A pan and a heating element fordrying samples.A balance or scales for weighingsamples.

FactorsThe soil properties that form the basis for

the Unified Soil Classification System arethe—

Percentage of gravels, sands, andfines.Shape of the grain-size distributioncurve.Plasticity.

These same properties are to be consideredin field identification. Other characteristicsobserved should also be included in describ-ing the soil, whether the identification ismade by field or laboratory methods.

Properties normally included in a descrip-tion of a soil are—

Color.Grain size, including estimated max-imum grain size and estimated percentby weight of fines (material passingthe Number 200 sieve),Gradation.Grain shape.Plasticity.Predominant type.Secondary components.Classification symbol.Other remarks, such as organic,chemical, or metallic content; com-pactness; consistency; cohesivenessnear PL; dry strength; and source—residual or transported (such aseolian, water-borne, or glacial de-posit).

An example of a soil description using thesequence and considering the propertiesreferred to above might be—

Dark brown to white.Coarse-grained soil, maximum par-ticle size 2 ¾ inches, estimating 60percent gravel, 36 percent sand, and4 percent passing the Number 200sieve.Poorly graded (insufficient fine gravel,gap-graded).Gravel particles subrounded torounded.

Soil Classification 5-18

FM 5-410

Nonplastic.Predominantly gravel.Considerable sand and a smallamount of nonplastic fines (silt).(GP)Slightly calcareous, no dry strength,dense in the undisturbed state.

A complete description with the proper clas-sification symbol conveys much more to thereader than the symbol or any other isolatedportion of the description used alone.

TestsThe following tests can be performed to aid

in field identification of soils:

Visual Examination Test. Determine thecolor, grain size, and grain shape of thecoarse-grained portion of a soil by visual ex-amination, The grain-size distribution maybe estimated. To observe these properties,dry a sample of the material and spread it ona flat surface.

In soil surveys in the field, color is oftenhelpful in distinguishing among various soilstrata, and from experience with local soils,color may aid in identifying soil types. Sincethe color of a soil often varies with its mois-ture content, the condition of the soil whencolor is determined must always be recorded.Generally, more contrast occurs in thesecolors when the soil is moist, with all thecolors becoming lighter as the moisture con-tents are reduced. In fine-grained soils,certain dark or drab shades of gray or brown(including almost-black colors) are indicativeof organic colloidal matter ((OL) and (OH)).In contrast, clean and bright-looking colors(including medium and light gray, olivegreen, brown, red, yellow, and white) areusually associated with inorganic soils. Soilcolor may also indicate the presence of certainchemicals. Red, yellow, and yellowish-brownsoil may be a result of the presence of ironoxides. White to pinkish colors may indicatethe presence of considerable silica, calciumcarbonate, or (in some cases) aluminum com-pounds. Grayish-blue, gray, and yellowmottled colors frequently indicate poordrainage.

Estimate the maximum particle size foreach sample, thereby establishing the upperlimit of the grain-size distribution curve forthat sample. The naked eye can normally dis-tinguish the individual grains of soil down toabout 0,07 mm. All particles in the gravel andsand ranges are visible to the naked eye.Most of the silt particles are smaller than thissize and are invisible to the naked eye.Material smaller than 0.75 mm will pass theNumber 200 sieve.

Perform the laboratory mechanicalanalysis whenever the grain-size distributionof a soil sample must be determined accu-rately; however, the grain-size distributioncan be approximated by visual inspection.The best way to evaluate a material withoutusing laboratory equipment is to spread aportion of the dry sample on a flat surface.Then, using your hands or a piece of paper,separate the material into its various grain-size components. By this method, the gravelparticles and some of the sand particles canbe separated from the remainder. This will atleast give you an opportunity to estimatewhether the total sample is to be consideredcoarse-grained or fine-grained, depending onwhether or not more than 50 percent of thematerial would pass the Number 200 sieve.Percentage of values refers to the dry weightof the soil fractions indicated as compared tothe dry weight of the original sample. Agraphical summary of the procedure is shownin Figure 5-2, page 5-20.

If you believe the material is coarse-grained, then consider the following criteria:

Does less than 5 percent pass theNumber 200 sieve?Are the fines nonplastic?

If both criteria can be satisfied and thereappears to be a good representation of allgrain sizes from largest to smallest, withoutan excessive deficiency of any one size, thematerial may be said to be well-graded ((GW)or (SW)). If any intermediate sizes appear tobe missing or if there is too much of any onesize, then the material is poorly graded ((GP)or (SP)). In some cases, it may only be

Soil Classification 5-19

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Soil Classification 5-20

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possible to take a few of the standard sievesinto the field. When this is the case, take theNumber 4, Number 40, and Number 200sieves. The sample may be separated intogravels, sands, and fines by use of the Num-ber 4 and Number 200 sieves. However, ifthere is a considerable quantity of fines, par-ticularly clay particles, separation of the finescan only be readily accomplished by washingthem through the Number 200 sieve. In suchcases, a determination of the percentage offines is made by comparing the dry weight ofthe original sample with that retained on theNumber 200 sieve after washing. The dif-ference between these two is the weight of thefines lost in the washing process. To deter-mine the plasticity, use only that portion ofthe soil passing through a Number 40 sieve.

Estimating the grain-size distribution of asample using no equipment is probably themost difficult part of field identification andplaces great importance on the experience ofthe individual making the estimate. A betterapproximation of the relative proportions ofthe components of the finer soil fraction maysometimes be obtained by shaking a portionof this sample into a jar of water and allowingthe material to settle. It will settle in layers,with the gravel and coarse sand particles set-tling out almost immediately. The fine sandparticles settle within a minute; the silt par-ticles require as much as an hour; and the clayparticles remain in suspension indefinitely oruntil the water is clear. In using this method,remember that the gravels and sands settleinto a much more dense formation than eitherthe silts or clays.

The grain shape of the sand and gravel par-ticles can be determined by close examinationof the individual grains. The grain shape af-fects soil stability because of the increasedresistance to displacement found in the moreirregular particles. A material with roundedgrains has only the friction between the sur-faces of the particles to help hold them inplace. An angular material has this samefriction force, which is increased by the rough-ness of the surface. In addition, aninterlocking action is developed between theparticles, which gives the soil much greaterstability.

A complete description of a soil should in-clude prominent characteristics of theundisturbed material. The aggregate proper-ties of sand and gravel are describedqualitatively by the terms “loose,” “medium,”and “dense.” Clays are described as “hard,”“stiff,” “medium, ” and “soft.”

These characteristics are usually evaluatedon the basis of several factors, including therelative ease or difficulty of advancing thedrilling and sampling tools and the consis-tency of the samples. In soils that aredescribed as “soft,” there should be an indica-tion of whether the material is loose andcompressible, as in an area under cultivation,or spongy (elastic), as in highly organic soils.The moisture condition at the time of evalua-tion influences these characteristics andshould be included in the report.

Breaking or Dry Strength Test. Thebreaking test is performed only on materialpassing the Number 40 sieve. This test, aswell as the roll test and the ribbon test, is usedto measure the cohesive and plastic charac-teristics of the soil. The testis normally madeon a small pat of soil about ½ inch thick andabout 2 inches in diameter. The pat isprepared by molding a portion of the soil inthe wet plastic state into the size and shapedesired and then allowing the pat to dry com-pletely. Samples may be tested for drystrength in their natural conditions. Such atest may be used as an approximation; how-ever, it should be verified later by testing acarefully prepared sample.

After the prepared sample is thoroughlydry, attempt to break it using the thumb andforefingers of both hands (see Figure 5-3,page5-22). If it can be broken, try to powder it byrubbing it with the thumb and fingers of onehand.

Typical reactions obtained in this test forvarious types of soils are described below.

Very highly plastic soils. (CH); veryhigh dry strength, Samples cannot bebroken or powdered using finger pres-sure.

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Highly plastic soils, (CH); high drystrength. Samples can be broken withgreat effort but cannot be pow-dered.Medium plastic soils, (CL); mediumdry strength. Samples can be brokenand powdered with some effort.Slightly plastic soils, (ML), (MH), or(CL); low dry strength. Samples canbe broken quite easily and powderedreadily.Nonplastic soils, (ML) or (MH); verylittle or no dry strength. Samplescrumble and powder on being pickedup in the hands.

The breaking or dry strength test is one ofthe best tests for distinguishing betweenplastic clays and nonplastic silts or finesands. However, a word of caution is ap-propriate. Dry pats of highly plastic claysquite often display shrinkage cracks. Break-ing the sample along one of these cracks givesan indication of only a very small part of thetrue dry strength of the clay. It is importantto distinguish between a break along such acrack and a clean, fresh break that indicatesthe true dry strength of the soil.

Roll or Thread Test. The roll or thread testis performed only on material passing theNumber 40 sieve. Prepare the soil sample byadding water to the soil until the moisturecontent allows easy remolding of the soilwithout sticking to the fingers. This is

Soil Classification 5-22

sometimes referred to as being just below the“sticky limit.” Using a nonabsorbent surface,such as glass or a sheet of heavy coated paper,rapidly roll the sample into a thread ap-proximately 1/8 inch in diameter Figure 5-4.

A soil that can be rolled into a l/8-inch-diarneter thread at some moisture contenthas some plasticity. Materials that cannot berolled in this manner are nonplastic or havevery low plasticity. The number of times thatthe thread may be lumped together and therolling process repeated without crumblingand breaking is a measure of the degree ofplasticity of the soil. After the PL is reached,the degree of plasticity may be described asfollows:

Highly plastic soils, (CH). The soilmay be remolded into a ball and theball deformed under extreme pressureby the fingers without cracking orcrumbling.Medium plastic soils, (CL). The soilmay be remolded into a ball, but theball will crack and easily crumbleunder pressure of the fingers.Low plastic soils, (CL), (ML), or (MH).The soil cannot be lumped togetherinto a ball without completely break-ing up.Organic materials, (OL) or (OH).Soils containing organic materials ormica particles will form soft spongythreads or balls when remolded.Nonplastic soils, (ML) or (MH). Non-plastic soils cannot be rolled into athread at any moisture content.

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From this test, the cohesiveness of thematerial near the PL may also be described asweak, firm, or tough. The higher the positionof a soil on the plasticity chart, the stiffer arethe threads as they dry out and the tougherare the lumps if the soil is remolded after roll-ing.

Ribbon Test. The ribbon test is performedonly on the material passing the Number 40sieve. The sample prepared for use in thistest should have a moisture content slightlybelow the sticky limit. Using this material,form a roll of soil about ½ or ¾ inch indiameter and about 3 to 5 inches long. Placethe material in the palm of the hand and,starting with one end, flatten the roll, forminga ribbon 1/8 to ¼ inch thick by squeezing itbetween the thumb and forefinger (see Figure5-5). The sample should be handled carefullyto form the maximum length of ribbon thatcan be supported by the cohesive properties ofthe material. If the soil sample holdstogether for a length of 8 to 10 inches withoutbreaking, the material is considered to beboth plastic and highly compressive (CH).

If soil cannot be ribboned, it is nonplastic(ML) Or (MH). If it can be ribboned only withdifficulty into short lengths, the soil is con-sidered to have low plasticity (CL). The rolltest and the ribbon test complement eachother in giving a clearer picture of the degreeof plasticity of a soil.

Wet Shaking Test. The wet shaking test isperformed only on material passing the Num-ber 40 sieve. In preparing a portion of thesample for use in this test, moisten enoughmaterial with water to form a ball of materialabout ¾ inch in diameter. This sampleshould be just wet enough so that the soilwill not stick to the fingers when remolding(just below the sticky limit) (see Figure 5-6a,page 5-24).

Place the sample in the palm of your handand shake vigorously (see Figure 5-6b, page5-24). Do this by jarring the hand on the tableor some other firm object or by jarring itagainst the other hand. The soil has reactedto this test when, on shaking, water comes tothe surface of the sample producing a smooth,shiny appearance (see Figure 5-6c, page 5-24).This appearance is frequently described as“livery.” Then, squeeze the sample betweenthe thumb and forefinger of the other hand.The surface water will quickly disappear, andthe surface will become dull. The materialwill become firm and resist deformation.Cracks will occur as pressure is continued,with the sample finally crumbling like a brit-tle material. The vibration caused by theshaking of the soil sample tends to reorientthe soil grains, decrease voids, and forcewater that had been within these voids to thesurface. Pressing the sample between thefingers tends to disarrange the soil grains, in-crease the void space, and draw the water intothe soil. If the water content is still adequate,shaking the broken pieces will cause them toliquefy again and flow together. This processonly occurs when the soil grains are bulky andcohesionless.

Very fine sands and silts are readily iden-tified by the wet shaking test. Since it is rarethat fine sands and silts occur without someamount of clay mixed with them, there arevarying degrees of reaction to this test. Evena small amount of clay tends to greatly retardthis reaction. Descriptive terms applied tothe different rates of reaction to this testare—

Sudden or rapid.Sluggish or slow.No reaction.

Soil Classification 5-23

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Soil Classification 5-24

A sudden or rapid reaction to the shakingtest is typical of nonplastic fine sands andsilts. A material known as rock flour, whichhas the same size range as silt, also gives thistype of reaction.

A sluggish or slow reaction indicates slightplasticity, such as that which might be foundfrom a test of some organic or inorganic siltsor from silts containing a small amount ofclay.

Obtaining no reaction at all to this test doesnot indicate a complete absence of silt or finesand. Even a slight content of colloidal clayimparts some plasticity and slows the reac-tion to the shaking test. Extremely slow or noreaction is typical of all inorganic clays andhighly plastic clays.

Odor Test. Organic soils of the (OL) and(OH) groups have a distinctive musty, slight-ly offensive odor, which can be used as an aidin identifying such material. This odor isespecially apparent from fresh samples. Ex-posure to air gradually reduces the odor, butheating a wet sample rejuvenates the odor.Organic soils are undesirable as foundationor base course material and are usuallyremoved from the construction site.

Bite or Grit Test. The bite or grit test is aquick and useful method of distinguishingamong sands, silts, or clays. In this test, asmall pinch of the soil material is groundlightly between the teeth and identified.

A sandy soil may be identified because thesharp, hard particles of sand grate veryharshly between the teeth and will be highlyobjectionable. This is true even of the finesand.

The silt grains of a silty soil are so muchsmaller than sand grains that they do not feelnearly so harsh between the teeth. Siltgrains are not particularly objectionable, al-though their presence is still easily detected.

The clay grains of a clayey soil are not grittybut feel smooth and powdery, like flour, be-tween the teeth. Dry lumps of clayey soilsstick when lightly touched with the tongue.

FM 5-410

Slaking Test. The slaking test is useful indetermining the quality of certain shales andother soft rocklike materials. The test is per-formed by placing the soil in the sun or in anoven to dry and then allowing it to soak inwater for a period of at least 24 hours. Thestrength of the soil is then examined. Certaintypes of shale completely disintegrate, losingall strength.

Other materials that appear to be durablerocks may be crumbled and readily broken byhand after such soaking. Materials that havea considerable reduction in strength are un-desirable for use as base course materials.

Acid Test. The acid test is used to determinethe presence of calcium carbonate. It is per-formed by placing a few drops of HC1 on apiece of soil. A fizzing reaction (efferves-cence) to this test indicates the presence ofcalcium carbonate.

CAUTIONHC1 may cause burns. Use appropriate measuresto protect the skin and eyes. If it is splashed onthe skin or in the eyes, immediately flush withwater and seek medical attention.

Calcium carbonate is normally desirable ina soil because of the cementing action itprovides to add to the soil’s stability. In somevery dry noncalcareous soils, the absorptionof the acid creates the illusion of efferves-cence. This effect can be eliminated in drysoils by moistening the soil before applyingthe acid.

Since cementation is normally developedonly after a considerable curing period, it can-not be counted on for strength in mostmilitary construction. This test permits bet-ter understanding of what appears to beabnormally high strength values on fine-grained soils that are tested in-place wherethis property may exert considerable in-fluence.

Shine Test. The shine testis another meansof measuring the plasticity characteristics ofclays. A slightly moist or dry piece of highlyplastic clay will give a definite shine when

rubbed with a fingernail, a pocketknife blade,or any smooth metal surface. On the otherhand, a piece of lean clay will not display anyshine but will remain dull.

Feel Test. The feel test is a general-purposetest and one that requires considerable ex-perience and practice before reliable resultscan be obtained. This test will be used moreas familiarity with soils increases. Moisturecontent and texture can be readily estimatedby using the feel test.

The natural moisture content of a soil indi-cates drainage characteristics, nearness to awater table, or other factors that may affectthis property. A piece of undisturbed soil istested by squeezing it between the thumb andforefinger to determine its consistency. Theconsistency is described by such terms as“hard,” stiff,” “brittle,” “friabie,” “sticky,”“plastic,” or “soft.” Remold the soil by workingit in the hands and observing any changes.By this test, the natural water content is es-timated relative to the LL or PL of the soil.Clays that turn almost liquid on remolding areprobably near or above the LL. If the clay re-mains stiff and crumbles on being remolded,the natural water content is below the PL.

The term “texture,” as applied to the fine-grained portion of a soil, refers to the degree offineness and uniformity. Texture is describedby such expressions as “floury,” “smooth,”“gritty,” or “sharp, “ depending on the feelwhen the soil is rubbed between the fingers.Sensitivity to this sensation may be increasedby rubbing some of the material on a moretender skin area, such as the inside of thewrist. Fine sand will feel gritty. Typical drysilts will dust readily and feel relatively softand silky to the touch. Clay soils are pow-dered only with difficulty but become smoothand gritless like flour.

Hasty Field IdentificationWith the standard methods of field iden-

tification supplemented with a few simplifiedfield tests, an approximate and hasty clas-sification of almost any soil can be obtained.The simple or hasty tests outlined in Fig-ure 5-7, page 5-26, will, for the most part,

Soil Classification 5-25

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Soil Classification 5-26

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Soil Classification 5-27

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Soil Classification 5-28

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eliminate the need for specialized equipmentsuch as sieves. The results will give at least atentative classification to almost any soil.The schematic diagram in Figure 5-7, page5-26, may be used as a guide to the testing se-quence in the process of assigning a symbol toa sample of soil.

OPTIMUM MOISTURE CONTENT (OMC)To determine whether a soil is at or near

OMC, mold a golf-ball-size sample of the soilwith your hands. Then squeeze the ball be-tween your thumb and forefinger. If the ballshatters into several fragments of ratheruniform size, the soil is near or at OMC. If theball flattens out without breaking, the soil iswetter than OMC. If, on the other hand, thesoil is difficult to roil into a ball or crumblesunder very little pressure, the soil is drierthan OMC.

Section II. Other SoilClassification Systems

COMMONLY USED SYSTEMSInformation about soils is available from

many sources, including publications, maps,

and reports. These sources may be of value tothe military engineer in studying soils in agiven area. For this reason, it is importantthat the military engineer have someknowledge of other commonly used systems.Table 5-5 gives approximate equivalentgroups for the USGS, Revised Public RoadsSystem, and the Federal Aviation Ad-ministration (FAA) System.

Revised Public Roads SystemMost civil agencies concerned with high-

ways in the United States classify soil by theRevised Public Roads System. This includesthe Bureau of Public Roads and most of thestate highway departments. The PublicRoads System was originated in 1931. Part ofthe original system, which applied to uniformsubgrade soils, used a number of tables andcharts based on several routine soil tests topermit placing of a given soil into one of eightprincipal groups, designated A-1 throughA-8. The system was put into use by manyagencies. As time passed, it became apparentthat some of the groups were too broad incoverage because somewhat different soilswere classed in the same group. A number ofthe agencies using the system modified it to

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suit their purposes. Principal modificationsincluded breaking down some of the broadgroups into subgroups of more limited scope.The revisions culminated in a comprehensivecommittee report that appeared in theProceedings of the 25th Annual Meeting of theHighway Research Board (1945). This samereport contains detailed information relativeto the Airfield Classification System and theFederal Aviation Administration System.The Revised Public Roads System is primar-ily designed for the evaluation of subgradesoils, although it is useful for other purposesalso.

Basis. Table 5-6 shows the basis of theRevised Public Roads System. Soils areclassed into one of two very broad groups.They are—

Granular materials, which contain <35 percent of material passing aNumber 200 sieve.Silt-clay materials, which contain >35 percent of material passing aNumber 200 sieve.

There are seven major groups, numberedA-1 through A-7, together with a number ofsuggested subgroups. The A-8 group of the

original system, which contained the highlyorganic soils such as peat, is not included inthe revised system. The committee felt thatno group was needed for these soils because oftheir ready identification by appearance andodor. Whether a soil is silty or clayey dependson its PI. “Silty” is applied to material thathas a PI < 10 and “clayey” is applied to amaterial that has a PI 10.

Figure 5-8 shows the formula for groupindex and charts to facilitate its computation.The group index was devised to provide abasis for approximating within-group evalua-tions. Group indexes range from 0 for thebest subgrade soils to 20 for the poorest. In-creasing values of the group index withineach basic soil group reflect the combined ef-fects of increasing LLs and PIs anddecreasing percentages of coarse material indecreasing the load-carrying capacity of sub-grades. Figure 5-9, page 5-32, graphicallyshows the ranges of LL and PI for the silt-claygroups. It is particularly useful for subdivid-ing the soils of the A-7 group.

Procedure. Table 5-6 is used in a left-to-right elimination process, and the given soil isplaced into the first group or subgroup in

Soil Classification 5-30

FM 5-410

which it fits. In order to distinguish therevised from the old system, the group symbolis given, followed by the group index in paren-theses (for example, A-4(5)). The fact that theA-3 group is placed ahead of the A-2 groupdoes not imply that it is a better subgradematerial. This arrangement is used tofacilitate the elimination process. The clas-sification of some borderline soils requiresjudgment and experience. The assignment ofthe group designation is often accompaniedby the writing of a careful description, as inthe USCS. Detailed examples of the clas-sification procedure are given later in thischapter.

Agricultural Soil Classification SystemMany reports published for agricultural

purposes can be useful to the military en-gineer. Two phases of the soil classificationsystem used by agricultural soil scientists arediscussed here. These are—

Grain-size classification (texturalclassification).Pedological classification.

Textural Classification. Informationabout the two textural classification systemsof the US Department of Agriculture iscontained in Figure 5-10, page 5-33, andTable 5-7, page 5-34. The chart and table arelargely self-explanatory. The grain-sizelimits, which are applicable to the categoriesshown, are as follows:

Coarse gravel, retained on Number 4sieve.Fine gravel, passing Number 4 andretained on Number 10 sieve.Coarse sand, passing Number 10 andretained on Number 60 sieve.Fine sand, passing Number 60 andretained on Number 270 sieve (0.05mm).Silt, 0.05 to 0.005 mm.Clay, below 0.005 mm.

Pedological Classification. Soil profileand pedology were discussed in Chapter 1.Agricultural soil scientists have devised acomplete and complex system for describingand classifiing surface soils. No attempt will

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be made to discuss this system in detail here.The portion of the system in which engineersare principally interested refers to the termsused in mapping limited areas. Mapping isbased on—

Series.Type.Phase.

The designation known as soil series is ap-plied to soils that have the same genetichorizons, possess similar characteristics andprofiles, and are derived from the sameparent material. Series names follow no par-ticular pattern but are generally taken fromthe geographical place near where they werefirst found. The soil type refers to the textureof the upper portion of the soil profile.Several types may, and usually do, existwithin a soil series. Phase is variation, usu-ally of minor importance, in the soil type.

A mapping unit may be “Emmet loamysand, gravelly phase” or any one of the largenumber of similar designations. Soils giventhe same designation generally have the

same agricultural properties wherever theyare encountered. Many of their engineeringproperties may also be the same. The map-ping unit in which a given soil is placed isdetermined by a careful examination of thesoil sample obtained by using an auger to boreor by observing highway cuts, natural slopes,and other places where the soil profile is ex-posed. Particularly important factors are—

Color.Texture.Organic material.Consistency.

Other important factors are—Slope.Drainage.Vegetation.Land use.

Agricultural soil maps prepared from fieldsurveys show the extent of each importantsoil type and its geographical location.Reports that accompany the maps containword descriptions of the various types, somelaboratory test results, typical profiles, andsoil properties important to agricultural use.Frequently prepared on a county basis, soilsurveys (maps and reports) are available formany areas in the United States and in manyforeign countries. For installation projects,check with the Natural Resources Branch orLand Management Branch of the Directorateof Engineering and Housing for a copy of thesoil survey. For off-post projects, request acopy of the soil survey from the county SoilConservation Service (SCS). The informa-tion contained in the soil survey is directlyuseful to engineers.

Geological Soil ClassificationGeologists classify soils according to their

origin (process of formation) following a pat-tern similar to that used in Chapter 1. TM5-545 gives a geological classification of soildeposits and related information.

TYPICAL SOIL CLASSIFICATIONThe following paragraphs concern the clas-

sification of four inorganic soil types on the

Soil Classification 5-32

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basis of laboratory test data. Each soil is clas-sified under the Unified Soil ClassificationSystem, the Revised Public Roads System,and the Agricultural Soil Classification Sys-tem. Table 5-8, page 5-35, shows the infor-mation known about each soil.

Unified Soil Classification SystemThe results of the classification of the four

soil types under this system are as follows:

Soil Nunzber 1. The soil is fine-grained sincemore than half passes the Number 200 sieve.The LL is less than 50; therefore, it must be(ML) or (CL) since it is inorganic. On the plas-ticity chart, it falls below the A-line;therefore, it is a sandy silt (ML).

Soil Number 2. The soil is fine-grainedsince more than half passes the Number 200

sieve. The LL is more than 50; therefore, itmust be (MH) or (CH). On the plasticitychart, it falls above the A-line; therefore, it isa sandy clay (CH).

Soil Number 3. The soil is coarse-grainedsince very little passes the Number 200 sieve.It must be a sand since it all passes the Num-ber 10 sieve. The soil contains less than5 percent passing the Number 200 sieve;therefore, it must be either an (SW) or an (SP)(see Table 5-2, page 5-9). The value of Cu = 2will not meet requirements for (SW); there-fore, it is a poorly graded sand (SP).

Soil Number 4. The soil is coarse-grainedsince again very little passes the Number 200sieve. It must be a gravel since more thanhalf of the coarse fraction is larger than aNumber 4 sieve. Since the soil contains less

Soil Classification 5-33

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Soil Classification 5-34

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than 5 percent passing the Number 200 sieve, 35 percent passes a Number 200 sieve. Itit is either (GW) or (GP) (see Table 5-2, page meets the requirements of the A-4 group;5-9). It meets the gradation requirements therefore, it is A-4(3).relative to CU and CC; therefore, it is a well-graded gravel (GW).

Revised Public RoadsClassification System

The results of the classification of the foursoil types under this system are as follows:

Soil Number 1. To calculate the groupindex, refer to Figure 5-8, page 5-31. Fromchart A, read 0; from chart B, read 3; there-fore, the group index = 0 + 3 = 3. Table 5-6,page 5-30, shows by a left-to-right eliminationprocess, that the soil cannot be in one of thegranular materials groups, since more than

Soil Number 2. The group index= 8 + 10 =18. Table 5-6, page 5-30, shows that the soilfalls into the A-7 group, since this is the onlygroup that will permit a group index value ashigh as 18. Figure 5-9, page 5-32, shows thatit falls in the A-7-6 subgroup; therefore,A-7-6(18).

Soil Number 3. The group index= 0 + 0 = 0This is one of the soils described as granularmaterial. It will not meet the requirements ofan A-1 soil, since it contains practically nofines. It does not meet the requirements ofthe A-3 group; therefore, it is A-3(0) (see Table5-6, page 5-30).

Soil Classification 5-35

FM 5-410

Soil Number 4. The group index= 0 + 0 = 0.This is obviously a granular material andmeets the requirements of the A-l-a (0) (seeTable 5-6, page 5-30).

Agricultural SoilClassification System

Although the values are not given in theprevious tabulation, assume that 12 percentof Soil Number 1 and 35 percent of SoilNumber 2 are in the range of clay sizesthat is below 0.005 mm.

Soil Number 1. This soil contains 100 - 48.2= 51.8 percent sand, since the opening of aNumber 270 sieve is 0.05 mm. The soil is thencomposed of 52 percent sand, 36 percent silt,and 12 percent clay. Figure 5-10, page 5-33,classifies this soil as a sandy loam.

Soil Number 2. This soil contains ap-proximately 35 percent sand, 30 percent silt,

and 35 percent clay. Figure 5-10, page 5-33,classifies this soil as clay.

Soil Number 3. This soil is 99 percent sand;therefore, it can only be classified as sand.

Soil Number 4. This soil contains ap-proximately 70 percent coarse gravel, 14percent fine gravel, 13 percent sand, and 3percent silt and clay combined. It cannot beclassified by using Figure 5-10, page 5-33, be-cause the chart does not cover gravels andgravelly sands. Table 5-7, page 5-34, clas-sifies the material as gravel and sand.

COMPARISONOF CLASSIFICATION SYSTEMS

Table 5-9 is a summary of the classificationof the soils in question under the three dif-ferent classification systems considered.

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CHAPTER 6

C o n c e p t s o f S o i l

E n g i n e e r i n g

The military engineer encounters a widevariety of soils in varying physical states. Be-cause of the inherent variability of thephysical properties of soil, several tests andmeasurements within soils engineering weredeveloped to quantify these differences and toenable the engineer to apply the knowledge toeconomical design and construction. Thischapter deals with soil engineering concepts,to include settlement, shearing resistance,and bearing capacity, and their application inthe military construction arena.

Section I. Settlement

FACTORSThe magnitude of a soil’s settlement

depends on several factors, including—Density.Void ratio.Grain size and shape.Structure.Past loading history of the soil de-posit.Magnitude and method of applicationof the load.Degree of confinement of the soilmass.

Unless otherwise stated, it is assumed thatthe soil mass undergoing settlement is com-pletely confined, generally by the soil thatsurrounds it.

COMPRESSIBILIYCompressibility is the property of a soil that

permits it to deform under the action of an ex-ternal compressive load. Loads discussed inthis chapter are primarily static loads thatact, or may be assumed to act, verticallydownward. Brief mention will be made of theeffects of vibration in causing compression.The principal concern here is with the prop-erty of a soil that permits a reduction inthickness (volume) under a load like that ap-plied by the weight of a highway or airfield.The compressibility of the underlying soilmay lead to the settlement of such a struc-ture.

Compressive Load BehaviorIn a general sense, all soils are compres-

sible. That is, they undergo a greater orlesser reduction in volume under compressivestatic loads. This reduction in volume is at-tributed to a reduction in volume of the voidspaces in the soil rather than to any reductionin size of the individual soil particles or watercontained in the voids.

If the soil is saturated before the load is ap-plied, some water must be forced from thevoids before settlement can take place. Thisprocess is called consolidation. The rate ofconsolidation depends on how quickly thewater can escape, which is a function Of thesoil’s permeability.

Concepts of Soil Engineering 6-1

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Cohesionless SoilsThe compressibility of confined coarse-

grained cohesionless soils, such as sand andgravel, is rarely a practical concern. This isbecause the amount of compression is likelyto be small in a typical case, and any settle-ment will occur rapidly after the load isapplied. Where these soils are located belowthe water table, water must be able to escapefrom the stratum. In the case of coarsematerials existing above the water table andunder less than saturated conditions, the ap-plication of a static load results in therearrangement of soil particles. Thisproduces deformation without regard to mois-ture escape. So, generally speaking,settlement occurs during the period of loadapplication (construction). Deformationsthat are thus produced in sands and gravelsare essentially permanent in character.There is little tendency for the soil to return toits original dimensions or rebound when theload is removed. A sand mass in a compactcondition may eventually attain some degreeof elasticity with repeated applications ofload.

The compressibility of a loose sand depositis much greater than that of the same sand ina relatively dense condition. Generally,structures should not be located on loose sanddeposits. Avoid loose sand deposits if pos-sible, or compact to a greater density beforethe load is applied. Some cohesionless soils,including certain very fine sands and silts,have loose structures with medium settle-ment characteristics. Both gradation andgrain shape influence the compressibility of acohesionless soil. Gradation is of indirect im-portance in that a well-graded soil generallyhas a greater natural density than one ofuniform gradation. Soils that contain platyparticles are more compressible than thosecomposed entirely of bulky grains. A finesand or silt that contains mica flakes maybequite compressible.

Although soils under static loads are em-phasized here, the effects of vibration shouldalso be mentioned. Vibration during con-struction may greatly increase the density of

cohesionless soils. A loose sand deposit sub-jected to vibration after construction may alsochange to a dense condition. The latterchange in density may have disastrous effectson the structures involved. Cohesionlesssoils are usually compacted or “densified” as aplanned part of construction operations.Cohesive soils are usually insensitive to theeffects of vibrations.

CONSOLIDATIONConsolidation is the time-dependent

change in volume of a soil mass under com-pressive load that occurs when water slowlyescapes from the pores or voids of the soil.The soil skeleton is unable to support the loadand changes structure, reducing its volumeand producing vertical settlement.

Cohesive SoilsThe consolidation of cohesive, fine-grained

soils (particularly clays) is quite differentfrom the compression of cohesionless soils.Under comparable static loads, the consolida-tion of a clay may be much greater thancoarse-grained soils and settlement may takea very long time to occur. Structures oftensettle due to consolidation of a saturated claystratum. The consolidation of thick, compres-sible clay layers is serious and may causestructural damage. In uniform settlement,the various parts of a structure settle ap-proximately equal amounts. Such uniformsettlement may not be critical. Nonuniform,or differential, settlement of parts of a struc-ture due to consolidation causes seriousstructural damage. A highway or airfieldpavement may be badly damaged by the non-uniform settlement of an embankmentfounded on a compressible soil.

Consolidation TestsThe consolidation characteristics of a com-

pressible soil should be determined forrational design of many large structuresfounded on or above soils of this type. Con-solidation characteristics generally aredetermined by laboratory consolidation testsperformed on undisturbed samples. Thenatural structure, void ratio, and moisturecontent are preserved as carefully as possiblefor undisturbed samples. However, military

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soils analysts are not equipped or trained toperform consolidation tests.

Information on consolidation tests and set-tlement calculations for the design ofstructures to be built on compressible soilsmay be found in Naval Facilities EngineeringCommand Design Manual (NAVFAC DM)-7.1.

Section II. Shearing ResistanceIMPORTANCE

From an engineering viewpoint, one of themost important properties a soil possesses isshearing resistance or shear strength. Asoil’s shearing resistance under given condi-tions is related to its ability to withstandloads. The shearing resistance is especiallyimportant in its relation to the supportingstrength, or bearing capacity, of a soil used asabase or subgrade beneath a road, runway, orother structure. The shearing resistance isalso important in determining the stability ofthe slopes used in a highway or airfield cut orembankment and in estimating the pressuresexerted against an earth-retaining structure,such as a retaining wall.

LABORATORY TESTSThree test procedures are commonly used

in soil mechanics laboratories to determinethe shear strength of a soil. These are—

Direct shear test.Triaxial compression test.Unconfined compression test.

The basic principles involved in each ofthese tests are illustrated in the simplifieddrawings of Figure 6-1. Military soilsanalysts are not equipped or trained to per-form the direct shear or triaxial compressiontests. For most military applications, theCBR value of a soil is used as a measure ofshear strength (see TM 5-530).

A variation of the unconfined compressiontest can be performed by military soilsanalysts, but the results are ordinarily usedonly in evaluation of soil stabilization. Shear

strength for a soil is expressed as a combina-tion of an apparent internal angle of friction(normally associated with cohesive soils).

CALIFORNIA BEARING RATIOThe CBR is a measure of the shearing resis-

tance of a soil under carefully controlledconditions of density and moisture. The CBRis determined by a penetration shear test andis used with empirical curves for designingflexible pavements. Recommended designprocedures for flexible pavements are

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presented in TM 5-330. The CBR test proce-dure for use in design consists of the followingsteps:

Prepare soil test specimens.Perform penetration test on the pre-pared soil samples.Perform swell test on soil test speci-mens.

Although a standardized procedure hasbeen established for the penetration portionof the test, one standard procedure for thepreparation of test specimens cannot be estab-lished because soil conditions and con-struction methods vary widely. The soil testspecimen is compacted so it duplicates as nearlyas possible the soil conditions in the field.

In a desert environment, soil maybe com-pacted and tested almost completely dry. In awet area, soil should probably be tested at 100percent saturation. Although penetrationtests are most frequently performed onlaboratory-compacted test specimens, theymay also be performed on undisturbed soilsamples or on in-place soil in the field.Detailed procedures for conducting CBR testsand analyzing the data are in TM 5-330.Appendix A describes the procedure for ap-plying CBR test data in designing roads andairfields.

Column 15, Table 5-3, page 5-11, showstypical ranges in value of the field CBR forsoils in the USCS. Values of the field CBRmay range from as low as 3 for highly plastic,inorganic clays (CH) and some organic claysand silts (OH) to as high as 80 for well-gradedgravel and gravel-sand mixtures.

AIRFIELD INDEX (AI)Engineering personnel use the airfield cone

penetrometer to determine an index of soilstrengths (called Airfield Index) for variousmilitary applications.

Airfield Cone PenetrometerThe airfield cone penetrometer is compact,

sturdy, and simple enough to be used bymilitary personnel inexperienced in soil

strength determination. If used correctly, itcan serve as an aid in maintaining field con-trol during construction operations; however,this use is not recommended, because moreaccurate methods are available for use duringconstruction.

Description. The airfield cone pene-trometer is a probe-type instrument consist-ing of a right circular cone with a basediameter of 1/2 inch mounted on a graduatedstaff. On the opposite end of the staff are aspring, a load indicator, and a handle. Theoverall length of the assembled penetrometeris 36 1/8 inches. For ease in carrying, thepenetrometer can be disassembled into threemain pieces. They are—

Two extension staffs, each 12 5/8 in-ches long.One piece 14 3/4 inches long contain-ing the cone, handle, spring, and loadindicator.

The airfield cone penetrometer has a range ofzero to 15.

The airfield cone penetrometer must not beconfused with the trafficability pene-trometer, a standard military item includedin the Soil Test Set. The cone penetrometerused for trafficability has a dial-type loadindicator (zero to 300 range) and is equippedwith a cone 1/2 inch in diameter and across-sectional area of 0.2 square inch andanother cone 0.8 inch in diameter and a cross-sectional area of 0.5 square inch. If thetrafficability penetrometer is used tomeasure the AI, the readings obtained withthe 0.2-square-inch cone must be divided by20; the reading obtained with the 0.5-square-inch cone must be divided by 50.

Operation. Before the penetrometer is used,inspect the instrument to see that all jointsare tight and that the load indicator readszero. To operate the penetrometer, place yourpalms down symmetrically on the handle.Steady your arms against your thighs andapply force to the handle until a slow, steady,downward movement of the instrument oc-curs. Read the load indicator at the moment

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the base of the cone enters the ground (sur-face reading) and at desired depths at themoment the corresponding depth mark on theshaft reaches the soil surface. The reading ismade by shifting the line of vision from thesoil surface to the indicator just a momentbefore the desired depth is reached. Maxi-mum efficiency is obtained with a two-personteam in which one person operates and readsthe instrument while the other acts as a re-corder. One person can operate theinstrument and record the measurements bystopping the penetration at any intermediatedepth, recording previous readings, and thenresuming penetration. Observe the followingrules to obtain accurate data:

Make sure the instrument reads zerowhen suspended by the handle and15 when a 150-pound load is applied.Keep the instrument in a verticalposition while it is in use.Control the rate of penetration atabout 1/2 to 1 inch per second.(Slightly faster or slower rates willnot materially affect the readings,however. )If you suspect the cone is encounter-ing a stone or other foreign body atthe depth where a reading is desired,make another penetration nearby.Take readings at the proper depths.(Carelessness in determining depth isone significant source of error in theuse of the penetrometer. )

Maintenance. The airfield cone pene-trometer is simply constructed of durable me-tals and needs little care other than cleaningand oiling. The calibration should be checkedoccasionally. If an error in excess of about 5percent is noted, recalibrate the pene-trometer.

Soil-Strength EvaluationThe number of measurements to be made,

the location of the measurements, and othersuch details vary with each area to be ex-amined and with the time available. For thisreason, hard and fast rules for evaluating anairfield are not practical, but the following in-structions are useful:

Fine-Grained Soils. A reading near zerocan occur in a very wet soil; it cannot supporttraffic. A reading approaching 15 occurs indry, compact clays or silts and tightly packedsands or gravels. Most aircraft that might berequired to use an unpaved area could easilybe supported for a substantial number oflanding and takeoffs on a soil having an AI of15.

Soil conditions are extremely variable. Asmany penetrometer measurements should betaken as time and circumstances permit. Thestrength range and uniformity of an area con-trols the number of measurements necessary.Areas obviously too soft for emergency land-ing strips will be indicated after a fewmeasurements, as will areas with strengthsthat are more than adequate. In all areas, thespots that appear to be softest should betested first, since the softest condition of anarea controls suitability. Soft spots are notalways readily apparent. If the first testresults indicate barely adequate strength, theentire area should be examined. Penetra-tions in areas that appear to be firm anduniform may be few and widely spaced, per-haps every 50 feet along the proposedcenterline. In areas of doubtful strength, thepenetrations should be more closely spaced,and areas on both sides of the centerlineshould be investigated. No fewer than threepenetrations should be made at each locationand usually five are desirable. If time per-mits, or if inconsistencies are apparent, asmany as 10 penetrations should be made ateach test location.

Soil strength usually increases with depth;but in some cases, a soil has a thin, hard crustover a deep, soft layer or has thin layers ofhard and soft material. For this reason, eachpenetration should be made to a 24-inchdepth unless prevented by a very firm condi-tion at a lesser depth. When penetrationcannot be made to the full 24-inch depth, ahole should be dug or augured through thefirm materials, and penetrometer readingsshould be taken in the bottom of the hole toensure that no soft layer underlies the firmlayer. If possible, readings should be takenevery 2 inches from the surface to a depth of24 inches. Generally, the surface reading

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should be disregarded when figures areaveraged to obtain a representative AI.

In the normal soil condition, wherestrength increases with depth, the readingsat the 2- to 8-inch depths (4 to 10 inches fordry sands and for larger aircraft) should beused to designate the soil strength for airfieldevaluation. If readings in this critical layer atany one test location do not differ more than 3or 4 units, the arithmetic average of thesereadings can be taken as the AI for the areasrepresented by the readings. When the rangebetween the highest and lowest readings ismore than about 4, the engineer must usejudgment in arriving at a rating figure. Forconservatism, the engineer should leantoward the low readings.

In an area in which hard crust less thanabout 4 inches thick overlies a much softersoil, the readings in the crust should not beused in evaluating the airfield. For example,if a 3-inch-thick crust shows average readingsof 10 at the 2-inch depth and average read-ings of 5 below 3 inches, the area should beevaluated at 5. If the crust is more than about4 inches thick, it will probably play an impor-tant part in aircraft support. If the crust inthe above instance is 5 inches thick, therating of the field would then be abouthalfway between the 10 of the crust and the 5of the underlying soil or, conservatively, 7.Innumerable combinations of crust thicknessand strength and underlying soil strengthcan occur. Sound reasoning and engineeringjudgment should be used in evaluating suchareas.

In an area in which a very soft, thin layer isunderlain by a firmer layer, the evaluationalso is a matter of judgment. If, for example,there are 1 to 2 inches of soil with an indexaveraging about 5 overlying a soil with anindex of 10, rate the field at 10; but if this softlayer is more than about 4 inches thick, ratethe field at 5. Areas of fine-grained soils withvery low readings in the top 1 inch or more arelikely to be slippery or sticky, especially if thesoil is a clay.

Coarse-Grained Soils. When relativelydry, many sands show increasing AIs with

Concepts of Soil Engineering 6-6

depth, but the 2-inch depth index will often below, perhaps about 3 or 4, Such sands usuallyare capable of supporting aircraft that re-quire a much higher AI than 3 to 4, becausethe strength of the sand actually increasesunder the confining action of the aircrafttires. Generally, any dry sand or gravel isadequate for aircraft in the C-130 class,regardless of the penetrometer readings. Allsands and gravel in a “quick” condition (watermoving upward through them) must heavoided. Evaluation of wet sands should bebased on the penetrometer readings obtainedas described earlier.

Once the strength of the soil, in terms of AI,has been established by use of the airfieldcone penetrometer, the load-carryingcapability of this soil can be determined foreach kind of forward, support, or rear-areaairfield through use of the subgrade strengthrequirements curves. These curves are basedon correlations of aircraft performance andAIs. Unfortunately, these are not exact cor-relations uniquely relating aircraftperformance to AI. As soils vary in type andcondition from site to site, so varies the rela-tion of AI to aircraft performance. For thisreason, the curves may not accurately reflectperformance in all cases. These relationswere selected so that in nearly all casesaircraft performance will be equal to or betterthan that indicated.

CORRELATION BETWEEN CBR AND AlExpedient soil strength measurements in

this manual are treated in terms of AI. Meas-urement procedures using the airfieldpenetrometer are explained; however, in thereferences listed at the end of this manual,which cover less expedient constructionmethods, soil strength is treated in terms ofCBR. To permit translation between theCBR and the AI, a correlation is presented inFigure 6-2. This figure can be used for es-timating CBR values from AI determinations.This correlation has been established to yieldvalues of CBR that generally are conserva-tive. The tendency toward conservatism isnecessary because there is no uniquerelationship between these measurementsover a wide range of soil types. It follows that

FM 5-410

the curve should not be used to estimate AIvalues from CBR determinations since thesewould not be conservative.

Section III. Bearing Capacity

IMPORTANCEThe bearing capacity of a soil is its ability to

support loads that may be applied to it by anengineering structure, such as—

A building, a bridge, a highway pave-ment, or an airport runway and themoving loads that may be carriedthereon.An embankment.Other types of load.

A soil with insufficient bearing capacity tosupport the loads applied to it may simply failby shear, allowing the structure to move orsink into the ground. Such a soil may fail be-cause it undergoes excessive deformation,with consequent damage to the structure.Sometimes the ability of a soil to supportloads is simply called its stability. Bearingcapacity is directly related to the allowableload that may be safely placed on a soil. Thisallowable load is sometimes called the allow-able soil pressure.

Types of failure that may take place whenthe ultimate bearing capacity is exceeded areillustrated in Figure 6-3. Such a failure mayinvolve tipping of the structure, with a bulgeat the ground surface on one side of the struc-ture. Failure may also take place on anumber of surfaces within the soil, usually ac-companied by bulging of the ground aroundthe foundation. The ultimate bearingcapacity not only is a function of the natureand condition of the soil involved but alsodepends on the method of application of theload.

FOUNDATIONSThe principle function of a foundation is to

transmit the weight of a structure and theloads that it carries to the underlying soil orrock. A foundation must be designed to besafe against a shear failure in the underlyingsoil. This means that the load placed on thesoil must not exceed its ultimate bearingcapacity.

Shallow FoundationsA shallow foundation is one that is located

at, or slightly below, the surface of theground. A typical foundation of this type isseen in the shallow footings, either of plain orreinforced concrete, which may support a

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building. Footings are generally square orrectangular. Long continuous or strip foot-ings are also used, particularly beneathbasement or retaining walls. Another type ofshallow foundation is the raft or mat; it maycover a large area, perhaps the entire area oc-cupied by a structure.

Deep FoundationsWhen the surface soils at the site of a

proposed structure are too weak and com-pressible to provide adequate support, deepfoundations are frequently used to transferthe load to underlying suitable soils. Twocommon types of deep foundations are—

Pile.Pier.

Piles. Piles and pile foundations are verycommonly used in both military and civil con-struction. By common usage, a pile is aload-bearing member made of timber, con-crete, or steel, which is generally forced intothe ground. Piles are used in a variety offorms and for a variety of purposes. A pilefoundation is one or more piles used to sup-port a pier, or column, or a row of piles undera wall. Piles of this type are normally used tosupport vertical loads, although they mayalso be used to support inclined or lateral for-ces.

Piles driven vertically and used for thedirect support of vertical loads are commonlycalled bearing piles. They may be used totransfer the load through a soft soil to an un-derlying firm stratum. These are calledend-bearing piles. Bearing piles may also beused to distribute the load through relativelysoft soils that are not capable of supportingconcentrated surface loads. These are calledfriction piles. A bearing pile may sometimesreceive its support from a combination of endbearing and friction. Bearing piles also maybe used where a shallow foundation wouldlikely be undetermined by scour, as in thecase of bridge piers. Bearing piles are il-lustrated in Figure 6-4.

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A typical illustration of an end-bearing pileis when a pile driven through a very soft soil,such as a loose silt or the mud of a river bot-tom, comes to rest on firm stratum beneath.The firm stratum may, for example, be rock,sand, or gravel. In such cases, the pile derivespractically all its support from the underlyingfirm stratum.

A friction pile develops its load-carryingcapacity entirely, or principally, from skinfriction along the sides of the pile. The load istransferred to the adjoining soil by friction be-tween the pile and the surrounding soil. Theload is thus transferred downward andlaterally to the soil. The soil surrounding thepile or group of piles, as well as that beneaththe points of the piles, is stressed by the load.

Some piles carry a load by a combination offriction and end bearing. A pile of this sortmay pass through a fairly soft soil thatprovides some frictional resistance; then itmay pass into a firm layer that develops load-carrying capacity through a combination offriction over a relatively short length of em-bedment and end bearing.

Piles are used for many purposes otherthan support for vertical loads. Piles that aredriven at an angle with the vertical are com-monly called batter piles. They may be usedto support inclined loads or to provide lateralloads. Piles are sometimes used to supportlateral loads directly, as in the pile fendersthat may be provided along waterfront struc-tures to take the wear and shock of dockingships. Sometimes piles are used to resist up-ward, tensile forces. These are frequentlycalled anchor piles. Anchor piles may beused, for example, as anchors for bulkheads,retaining walls, or guy wires. Vertical pilesare sometimes driven for the purpose of com-pacting loose cohesionless deposits. Closelyspaced piles, or sheet piles, may be driven toform a wall or a bulkhead that restrains a soilmass.

Piers. Piers are much less common thanpiles and are normally used only for the sup-port of very heavy loads.

Section IV. Earth-RetainingStructures

PURPOSEEarth-retaining structures must be used to

restrain a mass of earth that will not standunsupported. Such structures are commonlyrequired when a cut is made or when an em-bankment is formed with slopes too steep tostand alone.

Earth-retaining structures are subjected tolateral thrust from the earth masses thatthey support. The pressure of the earth onsuch a structure is commonly called lateralearth pressure. The lateral earth pressurethat may be exerted by a given soil on a givenstructure is a function of many variables. Itmust be estimated with a reasonable degreeof accuracy before an earth-retaining struc-ture may be properly designed. In manycases, the lateral earth pressure may be as-sumed to be acting in a horizontal directionor nearly so.

TYPESEarth-retaining structures discussed in

this section are retaining walls and bracingsystems used in temporary excavations.

Retaining WallsA retaining wall is a wall constructed to

support a vertical or nearly vertical earthbank that, in turn, may support verticalloads. Generally, retaining walls are clas-sified into the following five types (see Figure6-5, page 6-10):

Gravity.Cantilever.Counterfort.Buttressed.Crib.

When a retaining wall is used to supportthe end of a bridge span, as well as retain theearth backfill, it is called an abutment. Thereare several types of gravity retaining walls,such as—

Timber.Plain concrete.

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Gravity WallsPlain concrete or rubble, no tensile stress inany portion of the wall. Rugged construction isconservative but not economical for high walls.

Semigravity WallsA small amount of reinforcing steel is used forreducing the mass of concrete.

..7

Cantilever WallsIn the form of an inverted T, each projectingportion acts as a cantilever. It is usually madeof reinforced concrete. For small walls, rein-forced-concrete blocks may be used. Thistype is economical for walls of small tomoderate height (about 20-25 feet).

Counterfort WallsBoth base slab and face of wall span horizon-tally between vertical brackets known ascounterforts. This type is suitable for highretaining walls (greater than about 20 feet).

Buttressed WallsSimilar to the counterfoil wall except that thebackfill is on the opposite side of the verticalbrackets known as buttresses. Not commonlyused because of the exposed buttresses.

Crib WallsFormed by timber, precast concrete, or prefab-ricated steel members and filled with granularsoil. This type is suitable for walls of smallto moderate height (about 21 feet maximum)subjected to moderate earth pressure. Nosurcharge load except earth fill should beplaced directly above the crib wall.

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Sheet piling.Rubble.Stone or brick masonry.Crib.Gabions.

Retaining walls are used in many applica-tions. For example, a structure of this sortmay be used in a highway or railroad cut topermit the use of a steep slope and avoid ex-cessive amounts of excavation. Retainingwalls are similarly used on the embankmentside of sidehill sections to avoid excessivevolumes of fill. Bridge abutments and theheadwalls of culverts frequently function asretaining walls. In the construction of build-ings and various industrial structures,retaining walls are often used to provide sup-port for the side of deep, permanentexcavations.

Permanent retaining walls are generallyconstructed from plain or reinforced concrete;stone masonry walls are also used occasion-ally. In military construction, timber cribretaining walls are important. Their designis discussed later.

Backfills. The design of the backfill for aretaining wall is as important as the design ofthe wall itself. The backfill must be materialsthat are—

Reasonably clean.Granular.Essentially cohesionless.Easily drained.Not susceptible to frost action.

The best materials for backfills behindretaining walls are clean sands, gravels, andcrushed rock. In the USCS, the (GW) and(SW) soils are preferred, if they are available.The (GP) and (SP) soils are also satisfactory.These granular materials require compactionto make them stable against the effects ofvibration. Compaction also generally in-creases the angle of internal friction, which isdesirable in that it decreases the lateral pres-sure exerted on the wall. Materials of the(GM), (GC), (SM), and (SC) groups maybeused for backfills behind retaining walls, but

they must be protected against frost actionand may require elaborate drainageprovisions. Fine- grained soils are notdesirable as backfills because they are dif-ficult to drain. If clay soil must be used, thewall should be designed to resist earth pres-sures at rest. Ideal backfill materials arepurely granular soils containing < 5 percentof fines.

Backfills behind retaining walls are com-monly put in place after the structure hasbeen built. The method of compactiondepends on the—

Soil.Equipment available.Working space.

Since most backfills are essentiallycohesionless, they are best compacted byvibration. Equipment suitable for use withthese soils is discussed in Chapter 8. Com-mon practice calls for the backfill to be placedin layers of loose material that, when com-pacted, results in a compacted layer thicknessof from 6 to 8 inches. Each layer is compactedto a satisfactory density. In areas inacces-sible to rollers or similar compactingequipment, compaction may be done by theuse of mechanical air tampers or hand tools.

Drainage. Drainage of the backfill is essen-tial to keep the wall from being subjected towater pressure and to prevent frost action.Common drainage provisions used on con-crete walls are shown in Figure 6-6, page 6-12.

When the backfill is composed of clean,easily drained materials, it is customary toprovide for drainage by making weep holesthrough the wall. Weep holes are commonlymade by embedding pipes 4 to 6 inches indiameter into the wall. These holes arespaced from 5 to 10 feet center to center bothhorizontally and vertically. A filter ofgranular material should be provided aroundthe entrance to each weep hole to prevent thesoil from washing out or the drain from be-coming clogged. If possible, this materialshould conform to the requirements pre-viously given for filter materials.

Concepts of Soil Engineering 6-11

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Weep holes have the disadvantage of dis-charging the water that seeps through thebackfill at the toe of the wall where the soilpressures are greatest. The water mayweaken the soil at this point and cause thewall to fail. A more effective solution, whichis also more expensive, is to provide a lon-gitudinal back drain along the base of the wall(see Figure 6-6). A regular pipe drain should

be used, surrounded with a suitable filtermaterial. The drainage may be dischargedaway from the ends of the wall.

If a granular soil, which contains consider-able fine material and is poorly drained (suchas an (SC) soil) is used in the backfill, thenmore elaborate provisions may be installedto ensure drainage. One such approach is touse a drainage blanket (see Figure 6-6). If

Concepts of Soil Engineering 6-12

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necessary, a blanket of impervious soil orbituminous material may be used on top ofthe backfill to prevent water from enteringthe fill from the top. Such treatments arerelatively expensive.

Frost Action. Conditions for detrimentalfrost action on retaining walls include the fol-lowing:

A frost-susceptible soil.Availability of water.Freezing temperatures.

If these conditions are present in the backfill,steps must be taken to prevent the formationof ice lenses and the resultant severe lateralpressures that may be exerted against thewall. The usual way to prevent frost action isto substitute a thick layer of clean, granular,nonfrost-susceptible soil for the backfillmaterial immediately adjacent to the wall.The width of the layer should be as great asthe maximum depth of frost penetration inthe area (see Figure 6-7). As with other struc-tures, the bottom of a retaining wall should belocated beneath the line of frost penetration.

Timber Crib. A very useful type of retainingwall for military purposes in a theater ofoperations is timber cribbing. The crib, orcells, are filled with earth, preferably clean,coarse, granular material. A wall of this sortgains its stability through the weight of thematerial used to fill the cells, along with theweight of the crib units themselves. Thelongitudinal member in a timber crib is calleda stretcher, while a transverse member is aheader.

A principal advantage of a timber cribretaining wall is that it may be constructedwith unskilled labor and a minimum of equip-ment. Suitable timber is available in manymilitary situations. Little foundation ex-cavation is usually required and may belimited to shallow trenching for the lowerpart of the crib walls. The crib maybe built inshort sections, one or two cribs at a time.Where the amount of excavation is sufficientand suitable, the excavated soil may be usedfor filling the cells.

A crib of this sort maybe used on founda-tion soils that are weak and might not be ableto support a heavy wall, since the crib is fairlyflexible and able to undergo some settlementand shifting without distress. However, thisshould not be misunderstood, as the founda-tion soil must not be so soft as to permitexcessive differential settlement that woulddestroy the alignment of the crib.

Experience indicates that a satisfactorydesign will generally be achieved if the basewidth is a minimum of 4 feet at the top andbottom or 50 percent of the height of the wall,provided that the wail does not carry a sur-charge and is on a reasonably firmfoundation. If the wall carries a heavy sur-charge, the base width should be increased toa minimum of 65 percent of the height. In anycase, the width of the crib at the top and bot-tom should not be less than 4 feet.

Timber crib walls may be built with anydesired batter (receding upward slope) oreven vertical. The batter most often used andrecommended is one horizontal to four verti-cal (see Figure 6-8, page 6-14). If less batter isused, the base width must be increased to en-sure that the resultant pressure falls withinthe middle third of the base. The desired bat-ter is normally achieved by placing the baseon a slope equal to the batter. The toe maybeplaced on sills; this is frequently done withhigh walls. Sometimes double-cell construc-tion is used to obtain the necessary basewidth of high walls. The wall is thendecreased in width, or “stepped-back,” in theupper portions of the wall, above one thirdheight. Additional rows of bottom stretchers

Concepts of Soil Engineering 6-13

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may be used to decrease the pressure on thesoil or to avoid detrimental settlement.

The front and rear wall of the crib should beconnected at each panel point. The crib mustbe kept an essentially flexible structure andmust be free to move somewhat in any direc-tion, so as to adjust itself to thrusts andsettlements.

The material used in filling the cells shouldbe placed in thin layers and should be wellcompacted. Backfill behind the wall shouldalso be compacted and kept close to, but notabove, the level of the material in the cribs.Drainage behind timber crib walls may ormay not be required, depending on local con-ditions and wall construction.

Figure 6-8 shows the elevation and crosssection of a timber crib retaining wall, whichmay be used to a maximum height of about 16feet. A similar arrangement maybe used forheights up to about 8 feet, with a minimumwidth of 4 feet. For heights above 16 feet, theheaders are usually 6-inch by 12-inch timbers

and the stretchers 12-inch by 12-inch tim-bers. Timbers are normally connected bymeans of heavy (3/4-inch diameter) driftpins.

Other Timber Walls. Other types of timberretaining walls are used for low heights, par-ticularly in connection with culverts andbridges. A wall of this sort maybe built bydriving timber posts into the ground and at-taching planks or logs. Details on retainingwalls, used in conjunction with bridge abut-ments, are given in TM 5-312. Figure 6-9illustrates two other types of timber retainingwalls.

Gabions. Gabions are large, steel-wire-mesh baskets usually rectangular in shapeand variable in size (see Figure 6-10). Theyare designed to solve the problem of erosionat a low cost. Gabions were used in sixteenthcentury fortifications, and experience inconstruction with factory-produced prefabri-cated gabions dates back to 1894 in Italy.Gabions have been wideiy used in Europeand are now becoming accepted in theUnited States as a valuable and practical

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construction tool. They can be used in place ofsheet piling, masonry construction, or crib-bing. Gabions maybe used as—

Protective and antierosion structureson rivers (as revetments, groynes, orspurs).Channel linings.Seashore protection.Retaining walls for roads or railroads.Antierosion structures (such as weirs,drop structures, and check dams).Low-water bridges or fords.Culvert headwall and outlet struc-tures.Bridge abutments and wing walls.

The best use of gabions as retaining walls iswhere flexibility and permeability are impor-tant considerations, especially whereunstable ground and drainage conditions im-pose problems difficult to solve with rigid andimpervious material. Use of gabions does re-quire ready access to large-size stones, suchas those found in mountainous areas. Areasthat are prone to landslides have usedgabions successfully. Gabion walls have beenerected in mountainous country to trap fall-ing rocks and debris and in some areas to actas longitudinal drainage collectors.

The best filling material for a gabion is onethat allows flexibility in the structure but alsofills the gabion compartments with the mini-mum of voids and with the maximum weight.Ideally, the stone should be small, just slightlylarger than the size of the mesh. The stonemust be clean, hard, and durable to withstandabrasion and resistance to weathering andfrost action. The gabions are filled in threelifts, one foot at a time. Rounded stone, ifavailable, reduces the possibility of damage tothe wire during mechanical filling as com-pared with sharp quarry stone. If stone is notavailable, gabions can be filled with a goodquality soil. To hold soil, hardware cloth in-serts must be placed inside the gabions. Foruse in gabions, backfill material should meet

Concepts of Soil Engineering 6-15

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the following Federal Highway Administrat-ion criteria:

For a 6-inch sieve, 100 percent of thematerial should pass through.For a 3-inch sieve, 75 to 100 percentof the material should pass through.For a Number 200 sieve, zero to 25percent of the material should passthrough.The PI should be 6 or less.

Excavation Bracing SystemsBracing systems maybe required to protect

the sides of temporary excavations duringconstruction operations. Such temporary ex-cavations may be required for severalpurposes but are most often needed in connec-tion with the construction of foundations forstructures and the placing of utility lines,such as sewer and water pipes.

Shallow Excavations. The term “shallowexcavation” refers to excavations made todepths of 12 to 20 feet below the surface,depending principally on the soil involved.The lower limit applies to fairly soft clay soils,while the upper limit generally applies tosands and sandy soils.

Shallow excavations may be made as opencuts with unsupported slopes, particularlywhen the excavation is being done above thewater table, Chapter 10 gives recommendat-ions previously given relative to safe slopesin cuts that are applicable here if the excava-tion is to remain open for any length of time.If the excavation is purely temporary in na-ture, most sandy soils above the water tablewill stand at somewhat steeper slopes (asmuch as 1/2 to 1 for brief periods), althoughsome small slides may take place. Clays maybe excavated to shallow depths with verticalslopes and will remain stable briefly.Generally, bracing cuts in clay that extend todepths of 5 feet or more below the surface aresafer unless flat slopes are used.

Even for relatively shallow excavations,using unsupported cuts may be unsatisfac-tory for several reasons. Cohesive soils may

stand on steep slopes temporarily, but brac-ing is frequently needed to protect against asudden cave-in. Required side slopes, par-ticularly in loose, granular soils, may be soflat as to require an excessive amount of ex-cavation. If the excavation is being done closeto other structures, space maybe limited, orthe consequences of the failure of a side slopemay be very serious. Considerable sub-sidence of the adjacent ground may takeplace, even though the slope does not actuallyfail. Finally, if the work is being done belowthe water table, the excavation may have tobe surrounded with a temporary structurethat permits the excavation to be unwatered.

Narrow Shallow Excavations. Severaldifferent schemes may be used to brace thesides of a narrow shallow excavation. Two ofthese schemes are shown in Figure 6-11).

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In the first scheme, timber planks aredriven around the boundary of the excavationto form what is called vertical sheeting. Thebottom of the sheeting is kept at or near thebottom of the pit or trench as excavationproceeds. The sheeting is held in place bymeans of horizontal beams called wales.These wales are usually supported againsteach other by means of horizontal memberscalled struts, which extend from one side ofthe excavation to the other. The struts maybe cut slightly long, driven into place, andheld by nails or cleats. They may also be heldin position by wedges or shims. Hydraulic orscrew-type jacks can be used as struts.

The second scheme uses horizontal timberplanks to form what is called horizontal lag-ging. The lagging, in turn, is supported byvertical solid beams and struts. If the excava-tion is quite wide, struts may have to bebraced horizontally or vertically or both.

Bracing systems for shallow excavationsare commonly designed on the basis of ex-perience. Systems of this sort represent casesof incomplete deformation, since the bracingsystem prevents deformation at some pointswhile permitting some deformation at others.

Members used in bracing systems shouldbe strong and stiff. In ordinary work, strutsvary from 4-inch to 6-inch timbers for narrowcuts up to 8-inch by 8-inch timbers for excava-tions 10 or 12 feet wide. Heavier timbers areused if additional safety is desired. Struts arecommonly spaced about 8 feet horizontallyand from 5 to 6 feet vertically. Lagging or

sheeting is customarily made from planksfrom 6 to 12 inches wide, with the minimumthickness usually being about 2 inches.

Wide Shallow Excavations. If the excava-tion is too wide to be cross braced by the use ofstruts, vertical sheeting may be used (see Fig-ure 6-12). The wales are supported byinclined braces, which are sometimes calledrakes. The rakes, in turn, react against kick-er blocks that are embedded in the soil. Asthe excavation is deepened, additional walesand braces may be added as necessary to holdthe sheeting firmly in position. The success ofthis system depends on the soil in the bottomof the excavation being firm enough to pro-vide adequate support for the blocks.

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CHAPTER 7

M o v e m e n t o f W a t e r

T h r o u g h S o i l s

The movement of water into or through asoil mass is a phenomenon of great practicalimportance in engineering design and con-struction. It is probably the largest singlefactor causing soil failures. For example,water may be drawn by capillarity from a freewater surface or infiltrate through surfacecracks into the subgrade beneath a road orrunway. Water then accumulated may greatlyreduce the bearing capacity of subgrade soil,allowing the pavement to fail under wheelloads if precautions have not been taken indesign. Seepage flow may be responsible forthe erosion or failure of an open cut slope orthe failure of an earth embankment. Thischapter concerns the movement of water intoand through soils (and, to some extent, aboutthe practical measures undertaken to controlthis movement) and the problems associatedwith frost action.

Section I. WaterSOURCES OF WATER

Water in the soil maybe from a surface or asubsurface source.

Surface WaterWater enters through soil surfaces unless

measures are taken to seal the surface toprevent entry. Even sealed surfaces mayhave cracks, joints, or fissures that admitwater. In concrete pavement, for instance,

the contraction and expansion joints arepoints of entry for water. After the pavementhas been subjected to many cycies of expan-sion and contraction, the joint filler may beimperfect, thereby allowing water to seep intothe base course or subgrade.

Surface water may also enter from the sidesof the road or airfield, even though the surfaceitself is entirely adequate. To reduce this ef-fect, shoulders and ditches are sloped to carrythe water away at an acceptable rate. If ade-quate maintenance is not providedthroughout the life of the facility, vegetationor sedimentation may reduce the efficiency ofthe drainage so that water will frequentlystand in the drainage ditch. This water maythen be absorbed by the base and subgrade.

Subsurface WaterSubsurface moisture in soils may come

from one of the following sources:Free, or gravitional, water (controlledby the force of gravity).Hydroscopic moisture (controlled byforces of absorption).Capillary moisture (controlled by for-ces of capillarity).

Free, or Gravitational, Water. Water thatpercolates down from the surface eventuallyreaches a depth at which there is somemedium that restricts (to varying degrees)

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the further percolation of the moisture. Thismedium may be bedrock or a layer of soil, notwholly solid but with such small void spacesthat the water which leaves this zone is not asgreat as the volume or supply of water added.In time, the accumulating water completelysaturates the soil above the restrictingmedium and fills all voids with water. Whenthis zone of saturation is under no pressureexcept from the atmosphere, the water it con-tains is called free, or gravitational, water. Itwill flow through the soil and be resisted onlyby the friction between the soil grains and thefree water. This movement of free waterthrough a soil mass frequently is termedseepage.

The upper limit of the saturated zone of freewater is called the groundwater table, whichvaries with climatic conditions. During a wetwinter, the groundwater table rises. How-ever, a dry summer might remove the sourceof further accumulation of water. Thisresults in a decreased height of the saturatedzone, for the free water then flows downward,through, or along its restricting layer. Thepresence of impervious soil layers may resultin an area of saturated soil above the normalgroundwater table. This is called a “perched”water table.

Hydroscopic Moisture. When wet soil isair-dried, moisture is removed by evaporationuntil the hydroscopic moisture in the soil is inequilibrium with the moisture vapor in theair. The amount of moisture in air-dried soil,expressed as a percentage of the weight of thedry soil, is called the hydroscopic moisturecontent. Hydroscopic moisture films may bedriven off from air-dried soil by heating thematerial in an oven at 100 to 110 degrees Cen-tigrade (C) (210 to 230 degrees Fahrenheit(F)) for 24 hours or until constant weight is at-tained.

Capillary Moisture. Another source ofmoisture in soils results from what might betermed the capillary potential of a soil. Drysoil grains attract moisture in a mannersimilar to the way clean glass does. Outward

evidence of this attraction of water and glassis seen by observing the meniscus (curvedupper surface of a water column). Where themeniscus is more confined (for example, as ina small glass tube), it will support a column ofwater to a considerable height. The diagramin Figure 7-1 shows that the more the menis-cus is confined, the greater the height of thecapillary rise.

Capillary action in a soil results in the“capillary fringe” immediately above thegroundwater table. The height of the capil-lary rise depends on numerous factors. Onefactor worth mentioning is the type of soil.Since the pore openings in a soil vary with thegrain size, a fine-grained soil develops ahigher capillary fringe area than a coarse-grained soil. This is because the fine-grainedsoil can act as many very small glass tubes,each having a greatly confined meniscus. Inclays, capillary water rises sometimes as highas 30 feet, and in silts the rise is often as highas 10 feet. Capillary rise may vary from prac-tically zero to a few inches in coarse sands andgravels.

When the capillary fringe extends to thenatural ground surface, winds and hightemperatures help carry this moisture awayand reduce its effects on the soil. Once a pave-ment of watertight surface is applied,however, the effect of the wind and tempera-ture is reduced. This explains theaccumulation of moisture often found directlybeneath an impervious pavement.

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Capillary moisture in soils located abovethe water table may be visualized as occur-ring in the following three zones:

Capillary saturation.Partial capillary saturation.Contact moisture.

In the zone of capillary saturation, the soilis essentially saturated. The height of thiszone depends not only on the soil but also onthe history of the water table, since the heightwill be greater if the soil mass has beensaturated previously.

The height of the zone of partial capillarysaturation is likely to be considered greaterthan that of the zone of capillary saturation; italso depends on the water-table history. Itsexistence is the result of a few large voidsserving effectively to stop capillary rise insome parts of the soil mass. Capillary waterin this zone is still interconnected or “con-tinuous,” while the air voids may not be.

Above the zones of capillary and partialcapillary saturation, water that percolatesdownward from the surface may be held inthe soil by surface tension. It may fill thesmaller voids or be present in the form ofwater films between the points of contact ofthe soil grains. Water may also be broughtinto this zone from the water table byevaporation and condensation. This mois-ture is termed “contact moisture.”

One effect of contact moisture is apparentcohesion. An example of this is the behaviorof sand on certain beaches. On these beaches,the dry sand located back from the edge of thewater and above the height of capillary rise isgenerally dry and very loose and has littlesupporting power when unconfined. Closerto the water’s edge, and particularly duringperiods of low tide, the sand is very firm andcapable of supporting stationary or movingautomobiles and other vehicles. This ap-parent strength is due primarily to theexistence of contact moisture left in the voidsof the soil when the tide went out. The sur-face soil may be within the zone of partial orcomplete capillary saturation very close to

the edge of the water. Somewhat similarly,capillary forces may be used to consolidateloose cohesionless deposits of very fine sandsor silts in which the water table is at or nearthe ground surface. This consolidation is ac-complished by lowering the water table bymeans of drains or well points. If the opera-tion is properly carried out within the limitsof the height of capillary rise, the soil abovethe lowered water table remains saturated bycapillary moisture. The effect is to place thesoil structure under capillary forces (such astension in the water) that compress it. Thesoil may be compressed as effectively asthough an equivalent external load had beenplaced on the surface of the soil mass.

Methods commonly used to control thedetrimental effects of capillarity, particularlyconcerning roads and airport pavements, arementioned briefly here. Additional attentionis given to this subject in Section II, which isdevoted to the closely allied subject of frost ac-tion.

As has been noted, if the water table iscloser to the surface than the height of capil-lary rise, water will be brought up to thesurface to replace water removed by evapora-tion. If evaporation is wholly or partiallyprevented, as by the construction of imper-vious pavement, water accumulates and maycause a reduction in shearing strength orcause swelling of the soil. This is true par-ticularly when a fine-grained soil or a coarsesoil that contains a detrimental amount ofplastic fines is involved.

One obvious solution is to excavate thematerial that is subject to capillary action andreplace it with a granular material. This isfrequently quite expensive and usually maybe justified only in areas where frost action isa factor.

Another approach is to include in the pave-ment structure a layer that is unaffected bycapillary action. This is one of the functionsof the base that is invariably used in flexiblepavements. The base serves to interrupt theflow of capillary moisture, in addition to its

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other functions. Under certain circumstan-ces, the base itself may have to be drained toensure the removal of capillary water (seeFigure 7-2). This also is usually not justifiedunless other circumstances, such as frost ac-tion, are of importance.

Still another approach is to lower the watertable, which may sometimes be accomplishedby the use of side ditches. Subdrains maybeinstalled for the same purpose (see Figure 7-3,page 7-6). This approach is particularly effec-tive in relatively pervious or free-drainingsoils. Some difficulty may be experienced inlowering the water table by this method inflat country because finding outlets for thedrains is difficult. An alternative, used inmany areas where the permanent water tableis at or near the ground surface, is simply tobuild the highway or runway on a fill.Material that is not subject to detrimentalcapillarity is used to form a shallow fill. Thebottom of the base is normally kept a mini-mum of 3 or 4 feet above the natural groundsurface, depending on the soil used in the filland other factors. A layer of sand, known as asand blanket, or a geotextile fabric may beused to intercept capillary moisture, prevent-ing its intrusion into the base course.

PERMEABILITYPermeability is the property of soil that per-

mits water to flow through it. Water maymove through the continuous voids of a soil inmuch the same way as it moves through pipesand other conduits. As has been indicated,this movement of water through soils is fre-quently termed seepage and may also becalled percolation. Soils vary greatly in theirresistance to the flow of water through them.Relatively coarse soils, such as clean sandsand gravels, offer comparatively little resis-tance to the flow of water; these are said to bepermeable or pervious soils. Fine-grainedsoils, particularly clays, offer great resistanceto the movement of water through them andare said to be relatively impermeable or im-pervious. Some water does move throughthese soils, however. The permeability of asoil reflects the ease with which it can bedrained; therefore, soils are sometimesclassed as well-drained, poorly drained, or

Movement of Water Through Soils 7-4

impervious. Permeability is closely related tofrost action and to the settlement of soilsunder load.

The term k is called the coefficient of per-meability. It has units of velocity and mayberegarded as the discharge velocity under aunit hydraulic gradient. The coefficient ofpermeability depends on the properties of thefluid involved and on the soil. Since water isthe fluid normally involved in soil problems,and since its properties do not vary enough toaffect most practical problems, the coefficientof permeability is regarded as a property ofthe soil. Principal factors that determine thecoefficient of permeability for a given soil in-clude—

Grain size.Void ratio.Structure.

The relationships among these differentvariables for typical soils are quite complexand preclude the development of formulas forthe coefficient of permeability, except for thesimplest cases. For the usual soil, k is deter-mined experimentally, either in thelaboratory or in the field. These methods arediscussed briefly in the next paragraph.Typical values of the coefficient of per-meability for the soil groups of the USCS aregiven in column 8 of Table 5-4, page 5-15.

DRAINAGE CHARACTERISTICSThe general drainage characteristics of

soils classified under the USCS are given incolumn 12 of Table 5-3, page 5-11. Soils maybe divided into three general groups on thebasis of their drainage characteristics. Theyare—

Well-drained.Poorly drained.Impervious.

Well-Drained SoilsClean sands and gravels, such as those

included in the (GW), (GP), (SW), or (SP)groups, fail into the classification of well-drained soils. These soils may be drainedreadily by gravity systems. In road and

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airfield construction, for example, openditches may be used in these soils to interceptand carry away water that comes in from sur-rounding areas. This approach is veryeffective when used in combination with thesealing of the surface to reduce infiltrationinto the base or subgrade. In general, if thegroundwater table around the site of a con-struction project is controlled in these soils,then it will be controlled under the site also.

Poorly Drained SoilsPoorly drained soils include inorganic and

organic fine sands and silts, organic clays oflow compressibility, and coarse-grained soilsthat contain an excess of nonplastic fines.Soils in the (ML), (OL), (MH), (GM), (GC),(SC), and (SM) groups, and many from the(Pt) group, generally fall into this category.Drainage by gravity alone is likely to be quitedifficult for these soils.

Impervious SoilsFine-grained, homogeneous, plastic soils

and coarse-grained soils that contain plastic

fines are considered impervious soils. Thisnormally includes (CL) and (CH) soils andsome in the (OH) groups. Subsurfacedrainage is so slow on these items that it is oflittle value in improving their condition. Anydrainage process is apt to be difficult and ex-pensive.

FILTER DESIGNThe selection of the proper filter material is

of great importance since it largely deter-mines the success or failure of the drainagesystem. A layer of filter material ap-proximately 6 inches deep should be placedaround all subsurface piping systems. Theimproper selection of a filter material cancause the drainage system to become inopera-tive in one of three ways:

The pipe may become clogged by theinfiltration of small soil particles.Particles in the protected soil maymove into or through the filters, caus-ing instability of the surface.Free groundwater may not be able toreach the pipe.

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> 1.2

> 1

> 5

< 5

< 25

> 5

To prevent these failures from occurring,criteria have been developed based on thesoil’s gradation curve (see Chapter 5).

To prevent the clogging of a pipe by filtermaterial moving through the perforations oropenings, the following limiting require-ments must be satisfied (see EngineerManual (EM) 1110-2-1901):

For slotted openings:50 percent size of filter material

slot width

For circular holes:50 percent size of filter material

hole diameter

For porous concrete pipes:D85 filter (mm)

D15 aggregate (mm)

For woven filter cloths:D85 surrounding soil

Equivalent opening size (EOS) of cloth>1

To prevent the movement of particles fromthe protected soil into or through the filters,the following conditions must be satisfied:

15 percent of filter material85 percent size of protected soil

and50 percent size of filter material

50 percent size of protected soil

To permit free water to reach the pipe, thefilter material must be many times more per-vious than the protected soil. This conditionis fulfilled when the following requirement ismet:

15 percent size of filter material15 percent size of protected soil

If it is not possible to obtain a mechanicalanalysis of available filter materials and

protected soils, concrete sand with mechani-cal analysis limits as shown in Figure 7-4,page 7-8, may be used. Experience indicatesthat a well-graded concrete sand is satisfac-tory as a filter material in most sandy, siltysoils.

Section II. Frost ActionPROBLEMS

Frost action refers to any process that af-fects the ability of the soil to support astructure as a result of—

Freezing.Thawing.

A difficult problem resulting from frost actionis that pavements are frequently broken up orseverely damaged as subgrades freeze duringwinter and thaw in the spring. In addition tothe physical damage to pavements duringfreezing and thawing and the high cost oftime, equipment, and personnel required inmaintenance, the damage to communicationsroutes or airfields may be great and, in someinstances, intolerable strategically. In thespring or at other warm periods, thawing sub-grades may become extremely unstable. Insome severely affected areas, facilities havebeen closed to traffic until the subgraderecovered its stability.

The freezing index is a measure of thecombined duration and magnitude of below-freezing temperature occurring during anygiven freezing season. Figure 7-5, page 7-9,shows the freezing index for a specific winter.

FreezingEarly theories attributed frost heaves to

the expansion of water contained in soil voidsupon freezing. However, this expansionwould only be about 9 percent of the thicknessof a frozen layer if caused by the water in thesoil changing from the liquid to the solidstate. It is not uncommon to note heaves asgreat as 60 percent; under laboratory condi-tions, heaves of as much as 300 percent havebeen recorded. These facts clearly indicate

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that heaving is due to the freezing of addi-tional water that is attracted from the non-frozen soil layers. Later studies have shownthat frost heaves are primarily due to thegrowth of ice lenses in the soil at the plane offreezing temperatures.

The process of ice segregation may be pic-tured as follows: the thin layers of wateradhering to soil grains become supercooled,meaning that this water remains liquid below32 degrees Fahrenheit. A strong attractionexists between this water and the ice crystalsthat form in larger void spaces. This super-cooled water flows by capillary action towardthe already-formed crystals and freezes oncontact. Continued crystal growth leads tothe formation of an ice lens, which continues

to grow in thickness and width until thesource of water is cut off or the temperaturerises above the normal freezing point (see Fig-ure 7-6, page 7-10).

ThawingThe second phase of frost damage occurs

toward the end of winter or in early springwhen thawing begins. The frozen subgradethaws both from the top and the bottom. Forthe latter case, if the air temperature remainsbarely below the freezing point for a sufficientlength of time, deeply frozen soils graduallythaw from the bottom upward because of theoutward conduction of heat from the earth’sinterior. An insulating blanket of snowtends to encourage this type of thawing.From an engineering standpoint, this

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thawing condition is desirable, because it per- leaves a frozen layer beneath the thawed sub-mits melted water from thawed ice lenses toseep back through the lower soil layers to thewater table from which it was drawn duringthe freezing process. Such dissipation of themelted water places no load on the surfacedrainage system, and no tendency exists toreduce subgrade stability by reason of satura-tion. Therefore, there is little difficulty inmaintaining unpaved roads in a passable con-dition.

Thawing occurs from the top downward ifthe surface temperature rises from below thefreezing point to well above that point andremains there for an appreciable time. This

grade. The thawed soil between thepavement and this frozen layer contains anexcessive amount of moisture resulting fromthe melting of the ice it contained. Since thefrozen soil layer is impervious to the water,adequate drainage is almost impossible. Thepoor stability of the resulting supersaturatedroad or airfield subgrade accounts for manypavement failures. Unsurfaced earthenroads may become impassable when super-saturated.

Thawing from both the top and bottom oc-curs when the air temperature remainsbarely above the freezing point for a sufficient

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time. Such thawing results in reduced soilstability, the duration of which would be lessthan for soil where the thaw is only from thetop downward.

CONDITIONSTemperatures below 32 degrees Fahren-

hiet must penetrate the soil to cause freezing.In general, the thickness of ice layers (and theamount of consequent heaving) is inverselyproportional to the rate of penetration offreezing temperature into the soil. Thus,winters with fluctuating air temperatures atthe beginning of the freezing season produce

more damaging heaves than extremely cold,harsh winters where the water is more likelyto be frozen in place before ice segregation cantake place.

A source of water must be available topromote the accumulation of ice lenses.Water may come from—

A high groundwater table.A capillary supply from an adjoiningwater table.Infiltration at the surface.A water-bearing system (aquifer).Voids of fine-grained soils.

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Ice segregation usually occurs in soils whena favorable source of water and freezingtern peratures are present. The potential in-tensity of ice segregation in a soil dependslargely on the size of the void space and maybe expressed as an empirical fuction of grainsize.

Inorganic soils containing 3 percent ormore by weight of grains finer than 0.02 mmin diameter are generally considered frostsusceptible. Although soils may have as highas 10 percent by weight of grains finer than0.02 mm without being frost susceptible, thetendency of these soils to occur interbeddedwith other soils makes it impractical to con-sider them separately.

Frost-susceptible soils are classified in thefollowing groups:

F-1.F-2.F-3.F-4.

They are listed approximately in the orderof increasing susceptibility to frost heaving or

weakening as a result of frost melting (seeTable 7-1 ). The order of listing of subgroupsunder groups F-3 and F-4 does not necessarilyindicate the order of susceptibility to frostheaving or weakening of these subgroups.There is some overlapping of frost suscep-tibility between groups. The soils in groupF-4 are of especially high frost susceptibility.Soil names are defined in the USCS.

Varved clays consist of alternating layers ofmedium-gray inorganic silt and darker siltyclay. The thickness of the layers rarely ex-ceeds 1/2 inch, but occasionally much thickervarves are encountered. They are likely tocombine the undesirable properties of bothsilts and soft clays. Varved clays are likely tosoften more readily than homogeneous clayswith equal water content. However, local ex-perience and conditions should be taken intoaccount since, under favorable conditions (aswhen insufficient moisture is available forsignificant ice segregation), little or nodetrimental frost action may occur. Someevidence exists that pavements in theseasonal frost zone, constructed on varvedclay subgrades in which the deposit and

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depth to groundwater are relatively uniform,have performed satisfactorily. Where sub-grade conditions are uniform and localevidence indicates that the degree ofheave is not exceptional, the varved clay sub-grade soil should be assigned a group F-4frost-susceptibility classification.

EFFECTSFrost action can cause severe damage to

roads and airfields. The problems includeheaving and the resultant loss of pavementstrength.

HeavingFrost heave, indicated by the raising of the

pavement, is directly associated with icesegregation and is visible evidence on the sur-face that ice lenses have formed in thesubgrade material. Heave may be uniform ornonuniform, depending on variations in thecharacter of the soils and the groundwaterconditions underlying the pavement.

The tendency of the ice layers to developand grow increases rapidly with decreasinggrain size. On the other hand, the rate atwhich the water flows in an open systemtoward the zone of freezing decreases withdecreasing grain size. Therefore, it isreasonable to expect that the worst frostheave conditions would be encountered insoils having an intermediate grain size. Siltsoils, silty sands, and silty gravels tend to ex-hibit the greatest frost heave.

Uniform heave is the raising of adjacentareas of pavement surface by approximatelyequal amounts. In this type of heave, the in-itial shape and smoothness of the surfaceremains substantially unchanged. Whennonuniform heave occurs, the heave of ad-jacent areas is appreciably different,resulting in objectionable unevenness orabrupt changes in the grade at the pavementsurface.

Conditions conducive to uniform heavemay exist, for example, in a section of pave-ment constructed with a fairly uniform

Movement of Water Through Soils 7-12

stripping or fill depth, uniform depth togroundwater table, and uniform soil charac-teristics. Conditions conducive to irregularheave occur typically at locations where sub-grades vary between clean sand and silty soilsor at abrupt transitions from cut to fill sec-tions with groundwater close to the surface.

Lateral drains, culverts, or utility linesplaced under pavements on frost-susceptiblesubgrades frequently cause abrupt differen-tial heaving. Wherever possible, suchfacilities should not be placed beneath thesepavements, or transitions should be providedso as to moderate the roughening of the pave-ment during the period of heave.

Loss of Pavement StrengthWhen ice segregation occurs in a frost-sus-

ceptible soil, the soil’s strength is reduced asis the load-supporting capacity of the pave-ment during prolonged frost-melting periods.This often occurs during winter and springthawing periods, because near-surface icemelts and water from melting snow or rainmay infiltrate through the surface causing anexcess of water. This water cannot drainthrough the still-frozen soil below, or throughthe shoulders, or redistribute itself readily.The soil is thus softened.

Supporting capacity may be reduced in claysubgrades even through significant heavehas not occurred. This may occur becausewater for ice segregation is extracted from theclay lattice below, and the resultingshrinkage of the lattice largely balances thevolume of the ice lenses formed.

Further, traffic may cause remolding ordevelop hydrostatic pressure within the poresof the soil during the period of weakening,thus resulting in further-reduced subgradestrength. The degree to which a soil losesstrength during a frost-melting period andthe length of the period during which thestrength of the soil is reduced depend on—

The type of soil.Temperature conditions during freez-ing and thawing periods,

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The amount and type of traffic duringthe frost-melting periods.The availability of water during thefreezing and thawing periods.Drainage conditions.

Rigid Pavements (Concrete). Concretealone has only a little tensile strength, and aslab is designed to resist loads from abovewhile receiving uniform support from thesubgrade and base course. Therefore, slabshave a tendency to break up as a result of theupthrust from nonuniform heaving soilscausing a point bearing. As a rule, if rigidpavements survive the ill effects of upheaval,they will generally not fail during thawing.Reinforced concrete will carry a load by beamaction over a sub grade having either frozen orsupersaturated areas. Rigid pavements willcarry a load over subgrades that are bothfrozen and supersaturated. The capacity tobear the design load is reduced, however,when the rigid slab is supported entirely bysupersaturated, semiliquid subgrades.

Flexible Bituminous Pavements. Theductility of flexible pavements helps them todeflect with heaving and later resume theiroriginal positions. While heaving mayproduce severe bumps and cracks, usually itis not too serious for flexible pavements. Bycontrast, a load applied to poorly supportedpavements during the thawing period nor-mally results in rapid failure.

Slopes. Exposed back slopes and side slopesof cuts and fills in fine-g-rained soil have a ten-dency to slough off during the thawingprocess. The additional weight of water plusthe soil exceeds the shearing strength of thesoil, and the hydrostatic head of water exertsthe greatest pressure at the foot of the slope.This causes sloughing at the toe of the slope,which multiplies the failure by consecutiveshear failures due to inadequate stability ofthe altered slopes. Flatter slopes reduce thisproblem. Sustained traffic over severelyweakened areas afflicted with frost boils in-itiates a pumping action that results incomplete pavement failure in the immediatevicinity.

INVESTIGATIONAL PROCEDURESThe field and laboratory investigations con-

ducted according to Chapter 5 of this manualusually provide sufficient information todetermine whether a given combination ofsoil and water conditions beneath the pave-ment are conducive to frost action. Thisprocedure for determining whether the condi-tions necessary for ice segregation arepresent at a proposed site are discussed in thefollowing paragraphs. As stated earlier inthis chapter, inorganic soils containing 3 per-cent or more by weight of grains finer than0.02 mm are generally considered susceptibleto ice segregation. Thus, examination of thefine portion of the gradation curve obtainedfrom hydrometer analysis or the recantationprocess for these materials indicates whetherthey should be assumed frost susceptible. Inborderline cases, or where unusual materialsare involved, slow laboratory freezing testsmay be performed to measure the relativefrost susceptibility.

The freezing index value should be com-puted from actual daily air temperatures, ifpossible. Obtain the air temperatures from aweather station located as close as possible tothe construction site. Differences in eleva-tions, topographical positions, and nearnessof cities, bodies of water, or other sources ofheat may cause considerable variations infreezing indexes over short distances. Thesevariations are of greater importance to thedesign in areas of a mean design freezingindex of less than 100 (that is, a design freez-ing index of less than 500) than they arefarther north.

The depth to which freezing temperaturespenetrate below the surface of a pavementdepends principally on the magnitude andduration of below-freezing air temperaturesand on the amount of water present in thebase, subbase, and subgrade.

A potentially troublesome water supply forice segregation is present if the highestgroundwater at any time of the year is within5 feet of the proposed subgrade surface or thetop of any frost-susceptible base materials.When the depth to the uppermost water table

Movement of Water Through Soils 7-13

FM 5-410

is in excess of 10 feet throughout the year, asource of water for substantial ice segregationis usually not present unless the soil containsa significant percentage of silt. Inhomogeneous clay soils, the water contentthat the clay subgrade will attain under apavement is usually sufficient to providewater for some ice segregation even with aremote water table. Water may also enter afrost-susceptible subgrade by surface infiltra-tion through pavement areas. Figure 7-7illustrates sources of water that feed growingice lenses, causing frost action.

CONTROLAn engineer cannot prevent the temperat-

ures that cause frost action. If a road orrunway is constructed in a climate wherefreezing temperatures occur in winter, in allprobability the soil beneath the pavementwill freeze unless the period of loweredtemperatures is very short. However, severalconstruction techniques may be applied tocounteract the presence of water and frost-susceptible soils.

Every effort should be made to lower thegroundwater table in relation to the grade ofthe road or runway. This may be ac-complished by installing subsurface drains oropen side ditches, provided suitable outletsare available and that the subgrade soil isdrainable. The same result maybe achievedby raising the grade line in relation to thewater table. Whatever means are employedfor producing the condition, the distance fromthe top of the proposed subgrade surface (orany frost-susceptible base material used) tothe highest probably elevation of the watertable should not be less than 5 feet. Distancesgreater than this are very desirable if theycan be obtained at a reasonable cost.

Where it is possible, upward water move-ment should be prevented, In many cases,lowering the water table may not be practical.An example is in swampy areas where an out-lets for subsurface drains might not bepresent. One method of preventing the rise ofwater would be to place a 6-inch layer of per-vious, coarse-grained soil 2 or 3 feet beneaththe surface. This layer would be designed as

a filter to prevent clogging the pores withfiner material, which would defeat theoriginal purpose. If the depth of frostpenetration is not too great, it maybe less ex-pensive to backfill completely with granu-lar material. Another successful method,though expensive, is to excavate to thefrost line and backfill with granular material.In some cases, soil cement and asphalt-stabilized mixtures 6 inches thick have beenused effectively to cut off the upward move-ment of water.

Even though the site selected may be onideal soil, invariably on long stretches ofroads or on wide expanses of runways, local-ized areas will be subject to frost action.These areas should be removed and replacedwith select granular material. Unless this ismeticulously carried out, differential heavingduring freezing and severe strength loss uponthawing, may result.

The most generally accepted method ofpreventing subgrade failure due to frost ac-tion is to provide a suitable insulating cover tokeep freezing temperatures from penetratingthe subgrade to a significant depth. This in-sulating cover consists of a suitable thickpavement and a thick nonfrost-susceptiblebase course.

If the wearing surface is cleared of snowduring freezing weather, the shouldersshould also be kept free of snow. Where this isnot the case, freezing will set in first beneaththe wearing surface. This permits water to bedrawn into and accumulate in the subgradefrom the unfrozen shoulder area, which isprotected by the insulating snow. If bothareas are free of snow, then freezing willbegin in the shoulder area because it is notprotected by a pavement. Under this condi-tion, water is drawn from the subgrade to theshoulder area. As freezing progresses to in-clude the subgrade, there will be little frostaction unless more water is available fromgroundwater or seepage.

Base Composition RequirementsAll base and subbase course materials lying

within design depth of frost penetration

Movement of Water Through Soils 7-14

FM 5-410

Movement of Water Through Soils 7-15

FM 5-410

should be nonfrost-susceptible. Where thecombined thickness of pavement and base or-subbase over a frost-susceptible subgrade isless than the design depth of frost penetra-tion, the following additional designrequirements apply.

For both flexible and rigid pavements, thebottom 4 inches of base or subbase in contactwith the subgrade, as a minimum, will consistof any nonfrost-susceptible gravel, sand,screening, or similar material. This bottomof the base or subbase will be designed as a fil-ter between the subgrade soil and theoverlying material to prevent mixing of thefrost-susceptible subgrade with the nonfrost-susceptible base during and immediatelyafter the frost-melting period. The gradationof this filter material shall be determinedusing these guidelines:

To prevent the movement of particlesfrom the frost-susceptible subgradesoil into or through the filter blanket,all of these must be satisfied:15 percent size of filter blanket85 percent size of subgrade soil 5

50 percent size of filter blanket50 percent size of subgrade soil 25

The filter blanket in the above caseprevents the frost-susceptible soilfrom penetrating; however, the filtermaterial itself must also notpenetrate the nonfrost-susceptiblebase course material. Therefore, thefilter material must also meet the fol-lowing requirements:

15 percent size of base course85 percent size of filter blanket

5

50 percent size of base course50 percent size of filter blanket

25

In addition to the above require-ments, the filter material will, in nocase, have 3 percent or more byweight of grains finer than 0.02 mm.

A major difficulty in the construction of thefilter material is the tendency of the grain-size particles to segregate during placing;therefore, a CU > 20 is usually not desirable,For the same reason, filter materials shouldnot be skip- or gap-graded. Segregation ofcoarse particles results in the formation ofvoids through which fine particles may washaway from the subgrade soil. Segregation canbest be prevented during placement by plac-ing the material in the moist state. Usingwater while installing the filter blanket alsoaids in compaction and helps form satisfac-tory transition zones between the variousmaterials, Experience indicates that non-frost-susceptible sand is particularly suitablefor use as filter course material. Also fine-grained subgraded soil may workup into animproperly graded overlying gravel orcrushed stone base course. This will occurunder the kneading action of traffic duringthe frost-melting period if a filter course is notprovided between the subgrade and basecourse.

For rigid pavements, the 85-percent size offilter or regular base course material placeddirectly beneath pavement should be 2.00mm in diameter (Number 10 US standardsieve size) for a minimum thickness of 4 in-ches. The purpose of this requirement is toprevent loss of support by pumping soilthrough the joints.

Pavement DesignPavement may be designed according to

either of two basic concepts. The design maybe based primarily on—

Control of surface deformation causedby frost action.Provision of adequate bearing capac-ity during the most critical climaticperiod.

Control of Surface Deformation. In thismethod of pavement design, a sufficientcombined thickness of pavement and non-frost-susceptible base is provided to reduce

Movement of Water Through Soils 7-16

FM 5-410

subgrade frost penetration. Consequently, subgrade strength during the frost-meltingthis reduces pavement heave and subgrade period.weakening to a low, acceptable level.

Detailed design methods used in determin-Provision of Adequate Bearing Capacity. ing the required thickness of pavement, base,In this method, the amount of heave that will and subbase for given traffic and soil condi-result is neglected and the pavement is tions where frost action is a factor aredesigned solely on the anticipated reduced described in FM 5-430.

Movement of Water Through Soils 7-17

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Movement of Water Through Soils 7-1a

CHAPTER 7

Movement of WaterThrough Soils

The movement of water into or througha soil mass is a phenomenon of greatpractical importance in engineering de-sign and construction. It is probably thelargest single factor causing soil failures.For example, water may be drawn bycapillarity from a free water surface orinfiltrate through surface cracks into thesubgrade beneath a road or runway. Wa-ter then accumulated may greatly reducethe bearing capacity of subgrade soil, al-lowing the pavement to fail under wheelloads if precautions have not been takenin design. Seepage flow may be responsi-ble for the erosion or failure of an open cutslope or the failure of an earth embank-ment. This chapter concerns the move-ment of water into and through soils (and,to some extent, about the practical meas-ures undertaken to control this move-ment) and the problems associated withfrost action.

Section I. WaterKnowledge of the earth’s topography

and characteristics of geologic formationshelp the engineer find and evaluate watersources. Water in the soil may be from asurface or a subsurface source. Surfacewater sources (streams, lakes, springs)are easy to find. Finding subsurface watersources could require extensive searching.Applying geologic principles can helpeliminate areas where no large ground-water supplies are present and can indi-cate where to concentrate a search.

HYDROLOGIC CYCLE

Water covers 75 percent of the earth’ssurface. This water represents vast stor-age reservoirs that hold most of theearth’s water. Direct radiation from thesun causes water at the surface of rivers,lakes, oceans, and other bodies to changefrom a liquid to a vapor. This process iscalled evaporation. Water vapor rises inthe atmosphere and accumulates inclouds. When enough moisture accumu-lates in the clouds and the conditions areright, water is released as precipitation(rain, sleet, hail, snow). Some precipita-tion occurs over land surfaces and repre-sents the early stage of the land hydro-logic cycle. Precipitation that falls on landsurfaces is stored on the surface, flowsalong the surface, or flows into the groundas infiltration. Infiltration is a majorsource of groundwater and is often re-ferred to as recharge, because it replen-ishes or recharges groundwater resources.

The hydrologic cycle (Figure 7a, page 7-1b) consists of several processes. It doesnot usually progress through a regularsequence and can be interrupted or by-passed at any point. For example, rainmight fall in an area of thick vegetation,and a certain amount of this moisture willremain on the plants and not reach theground. The moisture could return to theatmosphere by direct evaporation,thereby causing a break in the hydrologiccycle. For the military engineer, the two

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Movement of Water Through Soils 7-b

most important states of this cycle arethose pertaining to surface runoff and wa-ter infiltration.

SURFACE WATER

Streams and lakes are the most avail-able and most commonly used sources formilitary water supplies. However, othersubsurface water sources should be con-sidered because long-term droughts couldoccur. Water naturally enters through soilsurfaces unless they are sealed; andsealed surfaces may have cracks, joints, orfissures that allow water penetration.Surface water may also enter from thesides of construction projects, such asroads or airfields.

Surface water is not chemically pure. Itmay contain sediment, bacteria, or dis-solved salts that make the water unfit forconsumption. Natural contamination andthe pollution that man causes are alsodangerous and occur in surface water.Test all surface water for purity and takeproper precautions before using it.

Streams

Streams normally supply an abundantquantity of water for the initial phase of afield operation. The water supply needs to

be adequate for the time of year the op-eration is planned. For a long-term sup-ply, you must learn the permanent statusof the stream flow.

Lakes

Most lakes are excellent sources of wa-ter. They serve as natural reservoirs forstoring large amounts of water. Lakes areusually more constant in quality than thestreams that feed them. Large lakes arepreferable because the water is usuallypurer. Shallow lakes and small ponds aremore likely to be polluted or contami-nated. Lakes located in humid regions aregenerally fresh and permanent. Lakes indesert regions are rare but can occur inbasins between mountains. These lakescould have a high percentage of dissolvedsalts and should not be considered as apermanent source of water.

Swamps

Swamps are likely to occur where wide,flat, poorly drained land and an abundantsupply of water exist. A large quantity ofwater is usually available in swamps; butit may be poor in quality, brackish, orsalty.

SPRINGS AND SEEPS

Water that naturally emerges at thesurface is called a spring if there is a dis-tinctive current, and a seep if there is nocurrent. Most springs and seeps consist ofwater that has slowly gravitated fromnearby higher ground. The water’s under-ground course depends on the permeabil-ity and structure of the material throughwhich it moves. Any spring that has atemperature higher than the yearly aver-age temperature of a given region istermed a thermal spring and indicates asource of heat other than the surface cli-mate.

Gravity Springs and Seeps

In gravity springs and seeps, subsurfacewater flows by gravity, not by hydrostaticpressure, from a high point of intake to a

Figure 7a. Hydrologic cycle

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Movement of Water Through Soils 7-1c

lower point of issue. Water-table springsand seeps are normally found around themargin of depressions, along the slope ofvalleys, and at the foot of alluvial fans.Contact springs appear along slopes, andmay be found at almost any elevation de-pending on the position of the rock for-mations.

Artesian Springs

When water is confined in a rock layerunder hydrostatic pressure, an artesiancondition is said to exist. A well drilledinto an aquifer where this condition ispresent, is called an artesian well (Figure7b). If the water rises to the surface, it iscalled an artesian spring. Certain situa-tions are necessary for an artesian condi-tion to exist—

• There must be a permeable aquiferthat has impervious layers aboveand below it to confine the water.

• There must be an intake area wherewater can enter the aquifer.

• A structural dip must exist so thathydrostatic pressure is produced inthe water at the lower areas of theaquifer.

GROUNDWATER

Groundwater or subsurface water isany water that exists below the earth’ssurface. Groundwater is located in twoprinciple zones in the earth’s surface—aeration and saturation (Figure 7c, page7-1d).

The zone of aeration consists of threemajor belts—soil moisture, intermediate,and capillary fringe. As water starts infil-trating the ground surface, it encountersa layer of organic matter. The root sys-tems of plants, decaying organic material,and the small pores found within the up-per soil zone hold some of the water insuspension. This shallow layer is calledthe soil moisture belt. The water passesthrough this belt and continues down-ward through the intermediate belt. Thepore spaces in this belt are generallylarger than those in the soil moisture belt,and the amount of organic material isconsiderably reduced. The intermediatebelt contains voids so it does not hold wa-ter, and the water gradually drainsdownward. The next belt is called the cap-illary fringe. Most deep-rooted plants sinkroots into this area.

Figure 7b. Artesian groundwater

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Movement of Water Through Soils 7-d

The water table is the contact betweenthe zone of aeration and the zone of satu-ration. It fluctuates up and down, depend-ing on the recharge rate and the rate offlow away from the area. The pores arefilled with water in the zone of saturation.

Free, or Gravitational, Water

Water that percolates down from thesurface eventually reaches a depth wherethere is some medium that restricts (tovarying degrees) the further percolation ofthe moisture. This medium may be bed-rock or a layer of soil, not wholly solid butwith such small void spaces that the wa-ter which leaves this zone is not as greatas the volume or supply of water added.In time, the accumulating water com-pletely saturates the soil above the re-stricting medium and fills all voids withwater. When this zone of saturation isunder no pressure except from the atmos-phere, the water it contains is called free,or gravitational, water. It will flowthrough the soil and be resisted only bythe friction between the soil grains andthe free water. This movement of free wa-ter through a soil mass frequently istermed seepage.

The upper limit of the saturated zone offree water is called the groundwater table,which varies with climatic conditions. During

a wet winter, the groundwater table rises.However, a dry summer might remove thesource of further accumulation of water.This results in a decreased height of thesaturated zone, for the free water thenflows downward, through, or along its re-stricting layer. The presence of impervi-ous soil layers may result in an area ofsaturated soil above the normal ground-water table. This is called a "perched" wa-ter table.

Hygroscopic Moisture

When wet soil is air-dried, moisture isremoved by evaporation until the hygro-scopic moisture in the soil is in equilib-rium with the moisture vapor in the air.The amount of moisture in air-dried soil,expressed as a percentage of the weight ofthe dry soil, is called the hygroscopicmoisture content. Hygroscopic moisturefilms may be driven off from air-dried soilby heating the material in an oven at 100to 110 degrees Centigrade (C) (210 to 230degrees Fahrenheit (F)) for 24 hours oruntil constant weight is attained.

Capillary Moisture

Another source of moisture in soils re-sults from what might be termed thecapillary potential of a soil. Dry soilgrains attract moisture in a manner

Figure 7c. Groundwater zones

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Movement of Water Through Soils 7-1e

similar to the way clean glass does. Out-ward evidence of this attraction of waterand glass is seen by observing the menis-cus (curved upper surface of a water col-umn). Where the meniscus is more con-fined (for example, as in a small glasstube), it will support a column of water toa considerable height. The diagram inFigure 7-1 shows that the more the me-niscus is confined, the greater the heightof the capillary rise.

Capillary action in a soil results in the"capillary fringe" immediately above thegroundwater table. The height of thecapillary rise depends on numerous fac-tors. One factor worth mentioning is thetype of soil. Since the pore openings in asoil vary with the grain size, a fine-grained soil develops a higher capillaryfringe area than a coarse-grained soil.This is because the fine-grained soil canact as many very small glass tubes, eachhaving a greatly confined meniscus. Inclays, capillary water rises sometimes ashigh as 30 feet, and in silts the rise is of-ten as high as 10 feet. Capillary rise mayvary from practically zero to a few inchesin coarse sands and gravels.

When the capillary fringe extends tothe natural ground surface, winds andhigh temperatures help carry this mois-ture away and reduce its effects on thesoil. Once a pavement of watertight sur-face is applied, however, the effect of thewind and temperature is reduced. Thisexplains the accumulation of moisture of-ten found directly beneath an imperviouspavement.

Capillary moisture in soils locatedabove the water table may be visualizedas occurring in the following three zones:

• Capillary saturation.

• Partial capillary saturation.

• Contact moisture.

In the zone of capillary saturation, thesoil is essentially saturated. The height ofthis zone depends not only on the soil butalso on the history of the water table,since the height will be greater if the soilmass has been saturated previously.

The height of the zone of partial capil-lary saturation is likely to be consideredgreater than that of the zone of capillarysaturation; it also depends on the water-table history. Its existence is the result ofa few large voids serving effectively tostop capillary rise in some parts of the soilmass. Capillary water in this zone is stillinterconnected or "continuous," while theair voids may not be.

Above the zones of capillary and par-tial capillary saturation, water that perco-lates downward from the surface may beheld in the soil by surface tension. It mayfill the smaller voids or be present in theform of water films between the points ofcontact of the soil grains. Water may alsobe brought into this zone from the watertable by evaporation and condensation.This moisture is termed "contact mois-ture."

One effect of contact moisture is appar-ent cohesion. An example of this is thebehavior of sand on certain beaches. Onthese beaches, the dry sand located backfrom the edge of the water and above theheight of capillary rise is generally dryand very loose and has little supportingpower when unconfined. Closer to the wa-ter's edge, and particularly during periodsof low tide, the sand is very firm and ca-pable of supporting stationary or moving

Figure 7-1. Capillary rise of moisture

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Movement of Water Through Soils 7-f

automobiles and other vehicles. This ap-parent strength is due primarily to theexistence of contact moisture left in thevoids of the soil when the tide went out.The surface soil may be within the zone ofpartial or complete capillary saturationvery close to the edge of the water. Some-what similarly, capillary forces may beused to consolidate loose cohesionless de-posits of very fine sands or silts in whichthe water table is at or near the groundsurface. This consolidation is accom-plished by lowering the water table bymeans of drains or well points. If the op-eration is properly carried out within thelimits of the height of capillary rise, thesoil above the lowered water table re-mains saturated by capillary moisture.The effect is to place the soil structureunder capillary forces (such as tension inthe water) that compress it. The soil maybe compressed as effectively as though anequivalent external load had been placedon the surface of the soil mass.

Methods commonly used to control thedetrimental effects of capillarity, particu-larly concerning roads and airport pave-ments, are mentioned briefly here. Addi-tional attention is given to this subject inSection II, which is devoted to the closelyallied subject of frost action.

As has been noted, if the water table iscloser to the surface than the height ofcapillary rise, water will be brought up tothe surface to replace water removed byevaporation. If evaporation is wholly orpartially prevented, as by the construc-tion of impervious pavement, water ac-cumulates and may cause a reduction inshearing strength or cause swelling of thesoil. This is true particularly when a fine-grained soil or a coarse soil that containsa detrimental amount of plastic fines isinvolved.

One obvious solution is to excavate thematerial that is subject to capillary actionand replace it with a granular material.This is frequently quite expensive andusually may be justified only in areaswhere frost action is a factor.

Another approach is to include in thepavement structure a layer that is unaf-fected by capillary action. This is one ofthe functions of the base that is invaria-bly used in flexible pavements. The baseserves to interrupt the flow of capillarymoisture, in addition to its other func-tions. Under certain circumstances, thebase itself may have to be drained to en-sure the removal of capillary water (seeFigure 7-2). This also is usually not justi-fied unless other circumstances, such asfrost action, are of importance.

Still another approach is to lower thewater table, which may sometimes be ac-complished by the use of side ditches.Subdrains may be installed for the samepurpose (see Figure 7-3, page 7-2). Thisapproach is particularly effective in rela-tively pervious or free-draining soils.Some difficulty may be experienced inlowering the water table by this methodin flat country because finding outlets forthe drains is difficult. An alternative,used in many areas where the permanentwater table is at or near the ground sur-face, is simply to build the highway orrunway on a fill. Material that is notsubject to detrimental capillarity is usedto form a shallow fill. The bottom of thebase is normally kept a minimum of 3 or 4feet above the natural ground surface, de-pending on the soil used in the fill andother factors. A layer of sand, known as asand blanket, or a geotextile fabric maybe used to intercept capillary moisture,preventing its intrusion into the basecourse.

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Movement of Water Through Soils 7-1g

Figure 7-2. Base drains in an airfield pavement

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Movement of Water Through Soils 7-2

Locating Groundwater Sources

Consider exploring rock aquifers onlywhen soil aquifers are not present orwhen the soil aquifer cannot provide therequired water supply. Identifying suit-able well sites in rock aquifers is muchmore difficult than in soil aquifers. Also,water development is usually more time-consuming and costly and has a higherrisk of failure. However, in some areas,rock aquifers are the only potential sourceof groundwater.

Hydrogeologic Indicators. Indicatorsthat help identify groundwater sourcesare referred to as hydrogeologic indicators(Table 7a). They are divided into threemajor groups—reservoir, groundwater,and boundary. Groundwater indicatorsare those conditions or characteristicsthat directly or indirectly indicategroundwater occurrence. No indicator is100 percent reliable, but the presence orabsence of certain indicators or associa-tions of indicators is fairly reliable.

Geologic Indicators. The type of rock orsoil present is an important indicator be-cause it usually defines the types of aqui-fers present and their water-producingcharacteristics. For field reconnaissance,the engineer need only recognize igneous,metamorphic, and sedimentary rocks andalluvium soil.

• Igneous rock. Usually a poor aquiferexcept where rock has been dis-turbed by faulting or fracturing. Ig-neous rock is normally incapable ofstoring or transmitting groundwaterand acts as a barrier to groundwaterflow.

• Metamorphic rock. Rarely capable ofproducing sufficient groundwaterand has poor potential for ground-water development. Metamorphicrock is considered to be an effectivebarrier to groundwater flow.

• Sedimentary rock. Has the greatestcapacity for holding groundwater.Unfractured sedimentary rock is ca-pable of supplying low well yields,

Figure 7-3. Typical subgrade drainage installation

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Movement of Water Through Soils 7-3

and fractured sedimentary rock iscapable of supplying moderate tohigh well yields.

• Alluvium soil. Groundwater is mostreadily available in areas that areunderlaid with alluvium. This islargely because uncemented orslightly cemented, compacted mate-rials have maximum pore space andare relatively shallow and easilypenetrated. The size of particles, thepercentage of fines, and the degreeof gradation have an importantbearing on the yield of groundwaterin soils. Clay yields almost no water;silt slowly yields some water, andwell-sorted, clean, coarse sand andgravel freely yield water. Alluvialvalleys are among the most produc-tive terrains for recovering ground-water.

PERMEABILITY

Permeability is the property of soil thatpermits water to flow through it. Watermay move through the continuous voids ofa soil in much the same way as it movesthrough pipes and other conduits. As hasbeen indicated, this movement of waterthrough soils is frequently termed seepage

and may also be called percolation. Soilsvary greatly in their resistance to the flowof water through them. Relatively coarsesoils, such as clean sands and gravels, of-fer comparatively little resistance to theflow of water; these are said to be perme-able or pervious soils. Fine-grained soils,particularly clays, offer great resistance tothe movement of water through them andare said to be relatively impermeable orimpervious. Some water does movethrough these soils, however. The perme-ability of a soil reflects the ease withwhich it can be drained; therefore, soilsare sometimes classed as well-drained,poorly drained, or impervious. Permeabil-ity is closely related to frost action and tothe settlement of soils under load.

The term k is called the coefficient ofpermeability. It has units of velocity andmay be regarded as the discharge velocityunder a unit hydraulic gradient. The co-efficient of permeability depends on theproperties of the fluid involved and on thesoil. Since water is the fluid normally in-volved in soil problems, and since itsproperties do not vary enough to affectmost practical problems, the coefficient ofpermeability is regarded as a property of

Table 7a. Hydrogeologic indicators for groundwater exploration

Reservoir Indicators Groundwater Indicators Boundary Indicators

Rock type/geometry Springs and seeps Location of recharge areas

Stratigraphic sequence Soil moisture Location of discharge areas

Degree of lithification Vegetation type Impermeable barriers

Grain size Vegetation density Semipermeable barriers

Fracture density Wetlands Surface-water divides

Dissolution potential Playas

Cumulative structure density Wells

Drainage basin size Reservoirs

Drainage basin elevation and relief Crop irrigation

Drainage pattern Salt encrustations

Drainage density Population distribution

Landforms Streams/rivers

Snow-melt patterns

Karst topography

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Movement of Water Through Soils 7-4

the soil. Principal factors that determinethe coefficient of permeability for a givensoil include—

• Grain size.

• Void ratio.

• Structure.

The relationships among these differ-ent variables for typical soils are quitecomplex and preclude the development offormulas for the coefficient of permeabil-ity, except for the simplest cases. For theusual soil, k is determined experimen-tally, either in the laboratory or in thefield. These methods are discussed brieflyin the next paragraph. Typical values ofthe coefficient of permeability for the soilgroups of the USCS are given in column 8of Table 5-4, page 5-15.

DRAINAGE CHARACTERISTICS

The general drainage characteristics ofsoils classified under the USCS are givenin column 12 of Table 5-3, page 5-11. Soilsmay be divided into three general groupson the basis of their drainage character-istics. They are—

• Well-drained.

• Poorly drained.

• Impervious.

Well-Drained Soils

Clean sands and gravels, such as thoseincluded in the (GW), (GP), (SW), or (SP)groups, fall into the classification of well-drained soils. These soils may be drainedreadily by gravity systems. In road andairfield construction, for example, openditches may be used in these soils to in-tercept and carry away water thatcomes in from surrounding areas. Thisapproach is very effective when usedin combination with the sealing of thesurface to reduce infiltration into the baseor subgrade. In general, if the groundwa-ter table around the site of a construction

project is controlled in these soils, then itwill be controlled under the site also.

Poorly Drained Soils

Poorly drained soils include inorganicand organic fine sands and silts, organicclays of low compressibility, and coarse-grained soils that contain an excess ofnonplastic fines. Soils in the (ML), (OL),(MH), (GM), (GC), (SC), and (SM) groups,and many from the (Pt) group, generallyfall into this category. Drainage by grav-ity alone is likely to be quite difficult forthese soils.

Impervious Soils

Fine-grained, homogeneous, plasticsoils and coarse-grained soils that containplastic fines are considered impervioussoils. This normally includes (CL) and(CH) soils and some in the (OH) groups.Subsurface drainage is so slow on theseitems that it is of little value in improvingtheir condition. Any drainage process isapt to be difficult and expensive.

FILTER DESIGN

The selection of the proper filter mate-rial is of great importance since it largelydetermines the success or failure of thedrainage system. A layer of filter materialapproximately 6 inches deep should beplaced around all subsurface piping sys-tems. The improper selection of a filtermaterial can cause the drainage system tobecome inoperative in one of three ways:

• The pipe may become clogged by theinfiltration of small soil particles.

• Particles in the protected soil maymove into or through the filters,causing instability of the surface.

• Free groundwater may not be ableto reach the pipe.

To prevent these failures from occur-ring, criteria have been developed basedon the soil's gradation curve (see Chapter5).

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Movement of Water Through Soils 7-5

To prevent the clogging of a pipe byfilter material moving through the perfo-rations or openings, the following limitingrequirements must be satisfied (see Engi-neer Manual (EM) 1110-2-1901):

• For slotted openings:

• For circular holes:

• For porous concrete pipes:

• For woven filter cloths:

To prevent the movement of particlesfrom the protected soil into or through the

filters, the following conditions must besatisfied:

and

To permit free water to reach the pipe,the filter material must be many timesmore pervious than the protected soil.This condition is fulfilled when the follow-ing requirement is met:

If it is not possible to obtain a me-chanical analysis of available filter mate-rials and protected soils, concrete sandwith mechanical analysis limits as shownin Figure 7-4, may be used. Experienceindicates that a well-graded concrete sandis satisfactory as a filter material in mostsandy, silty soils.

50 percent size of filter material

slot width 1.2>

50 percent size of filter material

hole diameter > 1

D filter (mm) D aggregate (mm)

> 585

15

D surrounding soilEquivalent opening size (EOS) of cloth

185

>

Figure 7-4. Mechanical analysis curves for filter material

15 percent of filter material85 percent size of protected soil

< 5

50 percent size of filter material50 percent size of protected soil

25<

15 percent size of filter material15 percent size of protected soil

> 5

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Movement of Water Through Soils 7-6

POROSITY AND PERMEABILITYOF ROCKS

Porosity and permeability determinethe water-bearing capability of a naturalmaterial.

Porosity

The amount of water that rocks cancontain depends on the open spaces intherock. Porosity is the percentage of thetotal volume of the rock that is occupiedby voids. Rock types vary greatly in size,number, and arrangement of their porespaces and, consequently, in their abilityto contain and yield water. The followinglist explains the porosity values of thetypes of rock displayed in Figure 7-4a.

• A and B—A decrease in porosity dueto compaction.

• C—A natural sand with high poros-ity due to good sorting.

• D—A natural sand with low porositydue to poor sorting and a matrix ofsilt and clay.

• E—Low porosity due to segmenta-tion.

• G—Porous zone between lava flows.• H—Limestone made porous by so-

lution along joints.• • I—Massive rock made porous by

fracturing.

Permeability

The permeability of rock is its capacityfor transmitting a fluid. The amount ofpermeability depends on the degree of po-rosity, the size and the shape of intercon-nections between pores, and the extent ofthe pore system.

WATER TABLE

In most regions, the depth that rocksare saturated with water depends largelyon the permeability of the rocks, theamount of precipitation, and the topogra-phy. In permeable rocks, the surface be-low where the rocks are saturated iscalled the water table (Figure 7b, page 7-1c). The water table is—

• Not a level surface.

• Irregular and reflects the surfacetopography.

• Relatively high beneath hills.

• Closer to the surface or approachingthe surface in valleys.

Perched Water Table

If impermeable layers are present, de-scending water stops at their upper sur-faces. If a water table lies well below thesurface, a mass of impermeable rock mayintercept the descending water and hold itsuspended above the normal saturatedzone. This isolated, saturated zone thenhas its own water table. Wells drilled intothis zone are poor quality, because thewell could quickly be drained of its watersupply.

Aquifer

An aquifer is a layer of rock below thewater table. It is also called a water-bearing formation or a water-bearingstratum. Aquifers can be found in almostany area; however, they are difficult tolocate in areas that do not have sedimen-tary rocks. Sands and sandstones usuallyconstitute the best aquifers, but any rockwith porosity and permeability can serveas a good water aquifer.Figure 7-4a. Porosity in rocks

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Saltwater Intrusion

There is always a danger of saltwaterintrusion into groundwater sources alongcoastal areas and on islands. Becausesaltwater is unfit for most human needs,contamination can cause serious prob-lems. When saltwater intrusion is discov-ered in the groundwater supply, deter-mine the cause and mitigate it as soon aspossible.

Section II. Frost ActionPROBLEMS

Frost action refers to any process thataffects the ability of the soil to support astructure as a result of—

• Freezing.

• Thawing.

A difficult problem resulting from frostaction is that pavements are frequentlybroken up or severely damaged as sub-grades freeze during winter and thaw inthe spring. In addition to the physicaldamage to pavements during freezing andthawing and the high cost of time, equip-ment, and personnel required in mainte-nance, the damage to communicationsroutes or airfields may be great and, insome instances, intolerable strategically.In the spring or at other warm periods,thawing subgrades may become ex-tremely unstable. In some severely af-fected areas, facilities have been closed totraffic until the subgrade recovered itsstability.

The freezing index is a measure of thecombined duration and magnitude of be-low-freezing temperature occurring dur-ing any given freezing season. Figure 7-5,page 7-9, shows the freezing index for aspecific winter.

Freezing

Early theories attributed frost heavesto the expansion of water contained in soilvoids upon freezing. However, this ex-pansion would only be about 9 percent of

the thickness of a frozen layer if caused bythe water in the soil changing from theliquid to the solid state. It is not uncom-mon to note heaves as great as 60 per-cent; under laboratory conditions, heavesof as much as 300 percent have been re-corded. These facts clearly indicate thatheaving is due to the freezing of addi-tional water that is attracted from thenonfrozen soil layers. Later studies haveshown that frost heaves are primarily dueto the growth of ice lenses in the soil atthe plane of freezing temperatures.

The process of ice segregation may bepictured as follows: the thin layers of wa-ter adhering to soil grains become super-cooled, meaning that this water remainsliquid below 32 degrees Fahrenheit. Astrong attraction exists between this wa-ter and the ice crystals that form in largervoid spaces. This supercooled water flowsby capillary action toward the already-formed crystals and freezes on contact.Continued crystal growth leads to theformation of an ice lens, which continuesto grow in thickness and width until thesource of water is cut off or the tempera-ture rises above the normal freezing point(see Figure 7-6, page 7-10).

Thawing

The second phase of frost damage oc-curs toward the end of winter or in earlyspring when thawing begins. The frozensubgrade thaws both from the top and thebottom. For the latter case, if the air tem-perature remains barely below the freez-ing point for a sufficient length of time,deeply frozen soils gradually thaw fromthe bottom upward because of the out-ward conduction of heat from the earth'sinterior. An insulating blanket of snowends to encourage this type of thawing.From an engineering standpoint, this

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CHAPTER 8

S o i l C o m p a c t i o n

Soil compaction is one of the most criticalcomponents in the construction of roads, air-fields, embankments, and foundations. Thedurability and stability of a structure are re-lated to the achievement of proper soilcompaction. Structural failure of roads andairfields and the damage caused by founda-tion settlement can often be traced back to thefailure to achieve proper soil compaction.

Compaction is the process of mechanicallydensifying a soil. Densification is ac-complished by pressing the soil particlestogether into a close state of contact with airbeing expelled from the soil mass in theprocess. Compaction, as used here, impliesdynamic compaction or densification by theapplication of moving loads to the soil mass.This is in contrast to the consolidation processfor fine-grained soil in which the soil isgradually made more dense as a result of theapplication of a static load. With relation tocompaction, the density of a soil is normallyexpressed in terms of dry density or dry unitweight. The common unit of measurement ispcf. Occasionally, the wet density or wet unitweight is used.

Section I. Soil PropertiesAffected by Compaction

ADVANTAGES OF SOIL COMPACTIONCertain advantages resulting from soil

compaction have made it a standard proce-dure in the construction of earth structures,

such as embankments, subgrades, and basesfor road and airfield pavements. No otherconstruction process that is applied to naturalsoils produces so marked a change in theirphysical properties at so low a cost as compac-tion (when it is properly controlled to producethe desired results). Principal soil propertiesaffected by compaction include—

Settlement.Shearing resistance.Movement of water.Volume change.

Compaction does not improve the desirableproperties of all soils to the same degree. Incertain cases, the engineer must carefullyconsider the effect of compaction on theseproperties. For example, with certain soilsthe desire to hold volume change to a mini-mum may be more important than just anincrease in shearing resistance.

SETTLEMENTA principal advantage resulting from the

compaction of soils used in embankments isthat it reduces settlement that might becaused by consolidation of the soil within thebody of the embankment. This is true be-cause compaction and consolidation bothbring about a closer arrangement of soil par-ticles.

Densification by compaction prevents laterconsolidation and settlement of an embank-ment. This does not necessarily mean thatthe embankment will be free of settlement; its

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weight may cause consolidation of compres-sible soil layers that form the embankmentfoundation.

SHEARING RESISTANCEIncreasing density by compaction usually

increases shearing resistance. This effect ishighly desirable in that it may allow the use ofa thinner pavement structure over a com-pacted subgrade or the use of steeper sideslopes for an embankment than would other-wise be possible. For the same density, thehighest strengths are frequently obtained byusing greater compactive efforts with watercontents somewhat below OMC. Large-scaleexperiments have indicated that the uncon-fined compressive strength of a clayey sandcould be doubled by compaction, within therange of practical field compaction proce-dures.

MOVEMENT OF WATERWhen soil particles are forced together by

compaction, both the number of voids con-tained in the soil mass and the size of theindividual void spaces are reduced. Thischange in voids has an obvious effect on themovement of water through the soil. One ef-fect is to reduce the permeability, thusreducing the seepage of water. Similarly, ifthe compaction is accomplished with propermoisture control, the movement of capillarywater is minimized. This reduces the ten-dency for the soil to take up water and sufferlater reductions in shearing resistance.

VOLUME CHANGEChange in volume (shrinkage and swelling)

is an important soil property, which is criticalwhen soils are used as subgrades for roadsand airfield pavements. Volume change isgenerally not a great concern in relation tocompaction except for clay soils where com-paction does have a marked influence. Forthese soils, the greater the density, thegreater the potential volume change due toswelling, unless the soil is restrained. An ex-pansive clay soil should be compacted at amoisture content at which swelling will notexceed 3 percent. Although the conditions

corresponding to a minimum swell and mini-mum shrinkage may not be exactly the same,soils in which volume change is a factorgenerally may be compacted so that these ef-fects are minimized. The effect of swelling onbearing capacity is important and isevaluated by the standard method used bythe US Army Corps of Engineers in preparingsamples for the CBR test.

Section II. DesignConsiderations

MOISTURE-DENSITY RELATIONSHIPSNearly all soils exhibit a similar relation-

ship between moisture content and drydensity when subjected to a given compactiveeffort (see Figure 8-1). For each soil, a maxi-mum dry density develops at an OMC for thecompactive effort used. The OMC at whichmaximum density is obtained is the moisturecontent at which the soil becomes sufficientlyworkable under a given compactive effort tocause the soil particles to become so closelypacked that most of the air is expelled. Formost soils (except cohesionless sands), whenthe moisture content is less than optimum,the soil is more difficult to compact. Beyondoptimum, most soils are not as dense under agiven effort because the water interferes withthe close packing of the soil particles. Beyondoptimum and for the stated conditions, the aircontent of most soils remains essentially thesame, even though the moisture content is in-creased.

The moisture-density relationship shownin Figure 8-1 is indicative of the workability ofthe soil over a range of water contents for thecompactive effort used. The relationship isvalid for laboratory and field compaction.The maximum dry density is frequentlyvisualized as corresponding to 100 percentcompaction for the given soil under the givencompactive effort.

The curve on Figure 8-1 is valid only for onecompactive effort, as established in thelaboratory. The standardized laboratorycompactive effort is the compactive effort(CE) 55 compaction procedure, which has

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been adopted by the US Army Corp of En-gineers. Detailed procedures for performingthe CE 55 compaction test are given in TM5-530. The maximum dry density (ydmax) atthe 100 percent compaction mark is usuallytermed the CE 55 maximum dry density, andthe corresponding moisture content is the op-timum moisture content. Table 8-1, page 8-4,shows the relationship between the US ArmyCorps of Engineers compaction tests andtheir civilian counterparts. Many times thenames of these tests are used interchange-ably in publications.

Figure 8-1 shows the zero air-voids curvefor the soil involved. This curve is obtained byplotting the dry densities corresponding tocomplete saturation at different moisturecontents. The zero air-voids curve representstheoretical maximum densities for givenwater contents. These densities are practi-cally unattainable because removing all the

air contained in the voids of the soil by com-paction alone is not possible. Typically, atmoisture contents beyond optimum for anycompactive effort, the actual compactioncurve closely parallels the zero air-voidscurve. Any values of the dry density curvethat plot to the right of the zero air-voidscurve are in error. The specific calculationnecessary to plot the zero air-voids curve arein TM 5-530.

Compaction Characteristicsof Various Soils

The nature of a soil itself has a great effecton its response to a given compactive effort!Soils that are extremely light in weight, suchas diatomaceous earths and some volcanicsoils, may have maximum densities under agiven compactive effort as low as 60 pcf.Under the same compactive effort, the maxi-mum density of a clay may be in the range of90 to 100 pcf, while that of a well-graded,

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coarse granular soil may be as high as 135 pcf.Moisture-density relationships for sevendifferent soils are shown in Figure 8-2.Compacted dry-unit weights of the soilgroups of the Unified Soil Classification Sys-tem are given in Table 5-2, page 5-8. Dry-unit weights given in column 14 are based oncompaction at OMC for the CE 55 compactiveeffort.

The curves of Figure 8-2 indicate that soilswith moisture contents somewhat less thanoptimum react differently to compaction.Moisture content is less critical for heavyclays (CH) than for the slightly plastic, clayeysands (SM) and silty sands (SC). Heavy claysmay be compacted through a relatively widerange of moisture contents below optimumwith comparatively small change in dry den-sity. However, if heavy clays are compactedwetter than the OMC (plus 2 percent), the soilbecomes similar in texture to peanut butterand nearly unworkable. The relatively clean,poorly graded sands also are relatively unaf-fected by changes in moisture. On the otherhand, granular soils that have better gradingand higher densities under the same cormpac-tive effort react sharply to slight changes in

moisture, producing sizable changes in drydensity.

There is no generally accepted and univer-sally applicable relationship between theOMC under a given compactive effort and theAtterberg limit tests described in Chapter 4.OMC varies from about 12 to 25 percent forfine-grained soils and from 7 to 12 percent forwell-graded granular soils. For some claysoils, the OMC and the PL will be ap-proximately the same.

Other Factors That Influence DensityIn addition to those factors previously dis-

cussed, several others influence soil density,to a smaller degree. For example, tempera-ture is a factor in the compaction of soils thathave a high clay content; both density andOMC may be altered by a great change intemperature. Some clay soils are sensitive tomanipulation; that is, the more they areworked, the lower the density for a given com-pactive effort. Manipulation has little effecton the degree of compaction of silty or cleansands. Curing, or drying, of a soil followingcompaction may increase the strength of

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subgrade and base materials, particularly ifcohesive soils are involved.

Addition of Water to SoilOften water must be added to soils being in-

corporated in embankments, subgrades, andbases to obtain the desired degree of compac-tion and to achieve uniformity. The soil canbe watered in the borrow pit or in place. Afterthe water is added, it must be thoroughlyand uniformly mixed with the soil. Even ifadditional water is not needed, mixing maystill be desirable to ensure uniformity. In

processing granular materials, the bestresults are generally obtained by sprinklingand mixing in place. Any good mixing equip-ment should be satisfactory. The more friablesandy and silty soils are easily mixed withwater. They may be handled by sprinklingand mixing, either on the grade or in the pit.Mixing can be done with motor graders,rotary mixers, and commercial harrows to adepth of 8 inches or more without difficulty.

If time is available, water may also beadded to these soils by diking or ponding the

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pit and flooding until the desired depth ofpenetration has taken place. This methodusually requires several days to accomplishuniform moisture distribution. Mediumclayey soils can be worked in the pit or in placeas conditions dictate. The best results are ob-tained by sprinkling and mixing withcultivators and rotary mixers. These soilscan be worked in lifts up to 8 inches or morewithout great difficulty. Heavy clay soilspresent many difficulties and should never beused as fill in an embankment foundation.They should be left alone without disturbancesince usually no compactive effort or equip-ment is capable of increasing the in-placecondition with reference to consolidation andshear strength.

The length of the section being rolled mayhave a great effect on densities in hot weatherwhen water evaporates quickly. When thiscondition occurs, quick handling of the soilmay mean the difference between obtainingadequate density with a few passes and re-quiring extra effort to add and mix water.

Handling of Wet SoilsWhen the moisture content of the soil to be

compacted greatly exceeds that necessary forthe desired density, some water must beremoved. In some cases, the use of exces-sively wet soils is possible without detrimen-tal effects. These soils (coarse aggregates)are called free-draining soils, and their maxi-mum dry density is unaffected by moisturecontent over a broad range of moisture. Mostoften, these soils must be dried; this can be aslow and costly process. The soil is usuallydried by manipulating and exposing it toaeration and to the rays of the sun.Manipulation is most often done with cul-tivators, plows, graders, and rotary mixers.Rotary mixers, with the tail-hood sectionraised, permit good aeration and are very ef-fective in drying excessively wet soils. Anexcellent method that may be useful whenboth wet and dry soils are available is simplyto mix them together.

Variation of Compactive EffortFor each compactive effort used in compact-

ing a given soil, there is a corresponding OMC

and maximum density. If the compactive ef-fort is increased, the maximum density isincreased and the OMC is decreased. Thisfact is illustrated in Figure 8-3. It showsmoisture-density relationships for two dif-ferent soils, each of which was compactedusing two different compactive efforts in thelaboratory. When the same soil is compactedunder several different compactive efforts, arelationship between density and compactiveeffort may be developed for that soil.

This information is of particular interest tothe engineer who is preparing specificationsfor compaction and to the inspector who mustinterpret the density test results made in thefield during compaction. The relationship be-tween compactive effort and density is notlinear. A considerably greater increase incompactive effort will be required to increasethe density of a clay soil from 90 to 95 percentof CE 55 maximum density than is required toeffect the same changes in the density of asand. The effect of variation in the compac-tive effort is as significant in the field rollingprocess as it is in the laboratory compactionprocedure. In the field, the compactive effortis a function of the weight of the roller and thenumber of passes for the width and depth ofthe area of soil that is being rolled. Increas-ing the weight of the roller or the number ofpasses generally increases the compactive ef-fort. Other factors that may be of consequenceinclude—

Lift thickness.Contact pressure. Size and length of the tamping feet(in the case of sheepsfoot rollers).Frequency and amplitude (in the caseof vibratory compactors).

To achieve the best results, laboratory andfield compaction must be carefully correlated.

COMPACTION SPECIFICATIONSTo prevent detrimental settlement under

traffic, a definite degree of compaction of theunderlying soil is needed. The degree dependson the wheel load and the depth below thesurface. For other airfield construction andmost road construction in the theater of oper-ations, greater settlement can be accepted,

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.

.

although the amount of maintenance willgenerally increase. In these cases, the mini-mum compaction requirements of Table 8-2,page 8-8, should be met. However. strengthcan possibly decrease with increased compac-tion. particularly with cohesive materials.As a result, normally a 5 percent compactionrange is established for density and a 4 per-cent range for moisture. Commonly, this“window” of density and moisture ranges isplotted directly on the GE 55 compactioncurve and is referred to as the specificationsblock. Figure 8-4, page 8-8, shows a density

range of 90 to 95 percent compaction and amoisture range of 12 to 16 percent.

CBR Design ProcedureThe concept of the CBR analysis was intro-

duced in Chapter 6. In the followingprocedures, the CBR analytical process willbe applied to develop soil compactionspecifications. Figure 8-5, page 8-10, outlinesthe CBR design process. The first step is tolook at the CE 55 compaction curve on a DDForm 2463, page 1. If it is U-shaped, the soilis classified as “free draining” for CBR

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analysis and the left-hand column of the flow-chart should be used through the designprocess. If it is bell-shaped, use the swell datagraphically displayed on a DD Form 1211.Soils that, when saturated, increase involume more than 3 percent at any initialmoisture content are classified as swellingsoils. If the percentage of swelling is ‹ 3 per-cent, the soil is considered nonswelling.

Regardless of the CBR classification of thesoil, the density value from the peak of the CE55 moisture density curve is ydmax. Thenext step is to determine the design moisturecontent range. For nonswelling soils, theOMC is used. When the OMC is used, thedesign moisture content range is + 2 percent.For swelling and free-draining soils, the min-imum moisture content (MMC) is used. TheMMC is determined differently for swellingsoils than it is for free-draining soils. TheMMC for swelling soils is determined by find-ing the point at which the 3 percent swelloccurs. The soil moisture content that cor-responds to the 3 percent swell is the MMC.Free-draining soils exhibit an increase indensity in response to increased soil moistureup to a certain moisture content, at whichpoint no further increase in density isachieved by increasing moisture. The mois-ture content that corresponds to ydmax is theMMC. For both swelling and free-drainingCBR soil classes, the design moisture-contentrange is MMC + 4 percent.

For swelling and free-draining soils, thefinal step in determining design compactionrequirements is to determine the densityrange. Free-draining soils are compacted to100-105 percent ydmax. Swelling soils arecompacted to 90-95 percent dmax.

Compaction requirement determinationsfor nonswelling soils require several additionalsteps. Once the OMC and design moisturecontent range have been determined, look at aDD Form 1207 for the PI of the soil. If PI > 5,the soil is cohesive and is compacted to 90-95percent ydmax. If the PI < 5, refer to the CBRFamily of Curves on page 3 of DD Form 2463.If the CBR values are insistently above 20,compact the soil to 100-105 percent ydmax. Ifthe CBR values are not above 20, compact thesoil to 95-100 percent

Once you have determined the design den-sity range and the moisture content range,you have the tools necessary to specify the re-quirements for and manage the compactionoperations. However, placing a particularsoil in a construction project is determined byits gradation. Atterberg limits, and designCBR value. Appendix A contains a discussionof the CBR design process.

A detailed discussion of placing soilsand aggregates in an aggregate surface or aflexible pavement design is in FM 5-430(for theater-of-operations construction),TM 5-822-2 (for permanent airfield design),and TM 5-822-5 (for permanent road design).

Subgrade CompactionIn fill sections, the subgrade is the top layer

of the embankment, which is compacted tothe required density and brought to thedesired grade and section. For subgrades,plastic soils should be compacted at moisturecontents that are close to optimum. Moisturecontents cannot always be carefully con-trolled during military construction, butcertain practical limits must be recognized.Generally, plastic soils cannot be compactedsatisfactorily at moisture contents more than10 percent above or below optimum. Muchbetter results are obtained if the moisturecontent is controlled to within 2 percent of op-timum. For cohesionless soils, moisturecontrol is not as important, but some sandstend to bulk at low moisture content. Com-paction should not be attempted until thissituation is corrected. Normally, cohesion-less soils are compacted at moisture contentsthat approach 100 percent saturation.

In cut sections, particularly when flexiblepavements are being built to carry heavywheel loads, subgrade soils that gain strengthwith compaction should be compacted to thegeneral requirements given earlier. Thismay make it necessary to remove the soil,replace it, and compact it in layers to obtainthe required densities at greater depths. Inmost construction in the theater of opera-tions, subgrade soil in cut sections should bescarified to a depth of about 6 inches andrecompacted. This is commonly referred to asa scarify/compact in-place (SCIP) operation.dmax.

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This procedure is generally desirable in theinterest of uniformity.

Expansive Clays. As indicated previously,soils that have a high clay content (partic-ularly (CH), (MH), and (OH)) may expand indetrimental amounts if compacted to a highdensity at a low moisture content and then ex-posed to water. Such soils are not desirable assubgrades and are difficult to compact. If theyhave to be used, they must be compacted tothe maximum density obtainable using theMMC that will result in a minimum amountof swelling. Swelling soils, if placed at mois-ture contents less than the MMC, can beexpected to swell more than 3 percent. Soilvolume increases of up to 3 percent generallydo not adversely affect theater-of-operationsstructures. This method requires detailedtesting and careful control of compaction. Insome cases, a base of sufficient thicknessshould be constructed to ensure against theharmful effects of expansion.

Clays and Organic Soils. Certain clay soilsand organic soils lose strength whenremolded. This is particularly true of some(CH) and (OH) soils. They have highstrengths in their undisturbed condition, butscarifying, reworking, and compacting themin cut areas may reduce their shearingstrengths, even though they are compacted todesign densities. Because of these qualities,they should be removed from the constructionsite.

Silts. When some silts and very fine sands(predominantly (ML) and (SC) soils) are com-pacted in the presence of a high water table,they will pump water to the surface and be-come “quick”, resulting in a loss of shearingstrength. These soils cannot be properly com-pacted unless they are dried. If they can becompacted at the proper moisture content.their shearing resistance is reasonably high.Every effort should be made to lower thewater table to reduce the potential of havingtoo much water present. If trouble occurswith these soils in localized areas, the soilscan be removed and replaced with moresuitable ones. If removal, or drainage andlater drying, cannot be accomplished, thesesoils should not be disturbed by attempting to

compact them. Instead, they should be left intheir natural state and additional covermaterial used to prevent the subgrade frombeing overstressed.

When these soils are encountered, theirsensitivity may be detected by performing un-confined compression tests on the un-disturbed soil and on the remolded soil com-pacted to the design density at the designmoisture content. If the undisturbed value ishigher, do not attempt to compact the soil;manage construction operations to producethe least possible disturbance of the soil.Base the pavement design on the bearingvalue of the undisturbed soil.

Base CompactionSelected soils that are used in base con-

struction must be compacted to the generalrequirements given earlier. The thickness oflayers must be within limits that will ensureproper compaction. This limit is generallyfrom 4 to 8 inches, depending on the materialand the method of construction.

Smooth-wheeled or vibratory rollers arerecommended for compacting hard, angularmaterials with a limited amount of fines orstone screenings. Pneumatic-tired rollers arerecommended for softer materials that maybreak down (degrade) under a steel roller.

Maintenance of Soil DensitySoil densities obtained by compaction

during construction may be changed duringthe life of the structure. Such considerationsare of great concern to the engineer engagedin the construction of semipermanent instal-lations, although they should be kept in mindduring the construction of any facility to en-sure satisfactory performance. The twoprincipal factors that tend to change the soildensity are—

Climate.Traffic.

As far as embankments are concerned, nor-mal embankments retain their degree ofcompaction unless subjected to unusual con-ditions and except in their outer portions,which are subjected to seasonal wetting and

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drying and frost action. Subgrades and basesare subject to more severe climatic changesand traffic than are embankments. Climaticchanges may bring about seasonal or per-manent changes in soil moisture andaccompanying changes in density, which maydistort the pavement surface. High-volume-change soils are particularly susceptible andshould be compacted to meet conditions ofminimum swelling and shrinkage. Granularsoils retain much of their compaction underexposure to climatic conditions. Other soilsmay be somewhat affected, particularly inareas of severe seasonal changes, such as—

Semiarid regions (where long, hot,dry periods may occur).Humid regions (where deep freezingoccurs).

Frost action may change the density of acompacted soil, particularly if it is fine-grained. Heavy traffic, particularly forsubgrades and bases of airfields, may bringabout an increase in density over that ob-tained during construction. This increase indensity may cause the rutting of a flexiblepavement or the subsidence of a rigid pave-ment. The protection that a subgrade soilreceives after construction is complete has animportant effect on the permanence of com-paction. The use of good shoulders, themaintenance of tight joints in a concretepavement, and adequate drainage all con-tribute toward maintaining the degree ofcompaction achieved during construction.

Section III. ConstructionProcedures

GENERAL CONSIDERATIONSThe general construction process of a

rolled-earth embankment requires that thefill be built in relatively thin layers or “lifts,”each of which is rolled until a satisfactory de-gree of compaction is obtained. The subgradein a fill section is usually the top lift in thecompacted fill, while the subgrade in a cutsection is usually compacted in in-place soil.Soil bases are normally compacted to a highdegree of density. Compaction requirements frequently stipulate a certain minimum density.

For military construction, this is generally aspecified minimum percentage of CE 55 max-imum density for the soil concerned. Themoisture content of the soil is maintained ator near optimum, within the practical limitsof field construction operations (normally + 2percent of the OMC). Principal types ofequipment used in field compaction aresheepsfoot, smooth steel-wheeled, vibratory,and pneumatic-tired rollers.

SELECTION OF MATERIALSSoils used in fills generally come from cut

sections of the road or airfield concerned,provided that this material is suitable. If thematerial excavated from cut sections is notsuitable, or if there is not enough of it, thensome material is obtained from other sources.Except for highly organic soils, nearly any soilcan be used in fills. However, some soils aremore difficult to compact than others andsome require flatter side slopes for stability.Certain soils require elaborate protectivedevices to maintain the fill in its original con-dition. When time is available, theseconsiderations and others may make it ad-vantageous to thoroughly investigateconstruction efforts, compaction charac-teristics, and shear strengths of soils to beused in major fills. Under expedient condi-tions, the military engineer must simplymake the best possible use of the soils athand.

In general terms, the coarse-grained soils ofthe USCS are desirable for fill construction,ranging from excellent to fair. The fine-grained soils are less desirable, being moredifficult to compact and requiring more care-ful control of the construction process. Table5-2, page 5-8, and Table 5-3, respectively con-tain more specific information concerning thesuitability of these soils.

DUMPING AND SPREADINGSince most fills are built up of thin lifts to

the desired height, the soil for each lift mustbe spread in a uniform layer of the desiredthickness. In typical operations, the soil isbrought in, dumped, and spread by scraperunits. The scrapers must be adjusted carefully

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to accomplish this objective. Materials mayalso be brought in by trucks or wagons anddumped at properly spaced locations so that auniform layer may be easily spread by bladegraders or bulldozers. Working alone,bulldozers may form very short and shallowfills. End dumping of soil material to form afill without compaction is rarely permitted inmodern embankment construction exceptwhen a fill is being built over very weak soils,as in a swamp. The bottom layers may thenbe end dumped until sufficient material hasbeen placed to allow hauling and compactingequipment to operate satisfactorily. The bestthickness of the layer to be used with a givensoil and a given equipment cannot be deter-mined exactly in advance. It is best deter-mined by trial during the early stages of roll-ing on a project. No lift, however, will have athickness less than twice the diameter of thelargest size particle in the lift. As stated pre-viously, compacted lifts will normally rangefrom 4 to 8 inches in depth (see Table 8-3, page8-13).

COMPACTION OF EMBANKMENTSIf the fill consists of cohesive or plastic soils,

the embankment generally must be built upof uniform layers (usually 4 to 6 inches incompacted thickness), with the moisture con-tent carefully controlled. Rolling should bedone with the sheepsfoot or tamping-footrollers. Bonding of a layer to the one placedon top of it is aided by the thin layer of loosematerial left on the surface of the rolled layerby the roller feet. Rubber-tired or smooth-wheeled rollers may be used to provide asmooth, dense, final surface. Rubber-tiredconstruction equipment may provide sup-plemental compaction if it is properly routedover the area.

If the fill material is clean sand or sandygravel, the moisture range at which compac-tion is possible is generally greater. Becauseof their rapid draining characteristics, thesesoils may be compacted effectively at or aboveOMC. Vibratory equipment may be used.Soils may be effectively compacted by com-bined saturation and the vibratory effects ofcrawler tractors, particularly when tractorsare operated at fairly high speeds so thatvibration is increased.

For adequate compaction, sands andgravels that have silt and clay fines requireeffective control of moisture. Certain soils ofthe (GM) and (SM) groups have especiallygreat need for close control. Pneumatic-tiredrollers are best for compacting these soils, al-though vibratory rollers may be usedeffectively.

Large rock is sometimes used in fills, par-ticularly in the lower portion. In some cases,the entire fill may be composed of rock layerswith the voids filled with smaller rocks or soiland only a cushion layer of soil for the sub-grade. The thickness of such rock layersshould not be more than 24 inches with thediameter of the largest rock fragment beingnot greater than 90 percent of the lift thick-ness. Compaction of this type of fill is difficultbut may generally be done by vibration fromthe passage of tack-type equipment over thefill area or possibly 50-ton pneumatic-tiredrollers.

Finishing in embankment construction in-cludes all the operations necessary tocomplete the earthwork. Included amongthese operations are the trimming of the sideand ditch slopes, where necessary, and thefine grading needed to bring the embankmentsection to final grade and cross section. Mostof these are not separate operations per-formed after the completion of otheroperations but are carried along as the workprogresses. The tool used most often infinishing operations is the motor grader,while scraper and dozer units may be used ifthe finish tolerances are not too strict. Theprovision of adequate drainage facilities is anessential part of the work at all stages of con-struction, temporary and final.

DENSITY DETERMINATIONSDensity determinations are made in the

field by measuring the wet weight of a knownvolume of compacted soil. The sample to beweighed is taken from a roughly cylindricalhole that is dug in the compacted layer. Thevolume of the hole may be determined by oneof several methods. including the use of—

Heavy oil of known specific gravity.Rubber balloon density apparatus.

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Calibrated sand.Nuclear densimeter.

When the wet weight and the volume areknown, the unit wet weight may then be cal-culated, as described in FM 5-430.

In very arid regions, or when working withsoils that lose strength when remolded, theadequacy of compaction should be judged byperforming the in-place CBR test on the com-pacted soil of a subgrade or base. The CBRthus obtained can then be compared with thedesign CBR, provided that the design wasbased on CBR tests on unsoaked samples. Ifthe design was based on soaked samples, theresults of field in-place CBR tests must be cor-related with the results of laboratory testsperformed on undisturbed mold samples ofthe in-place soil subjected to soaking.Methods of determining the in-place CBR of asoil are described in TM 5-530.

FIELD CONTROL OF COMPACTIONAs stated in previous paragraphs, specifica-

tions for adequate compaction of soiI used inmilitary construction generally require theattainment of a certain minimum density infield rolling. This requirement is most oftenstated in terms of a specified percentagerange of CE 55 maximum density. Withmany soils, the close control of moisture con-tent is necessary to achieve the stated densitywith the available equipment. Careful con-trol of the entire compaction process isnecessary if the required density is to beachieved with ease and economy. Controlgenerally takes the form of field checks ofmoisture and density to—

Determine if the specified density isbeing achieved.Control the rolling process.Permit adjustments in the field, as re-quired.

The following discussion assumes that thelaboratory compaction curve is available forthe soil being compacted so that the maxi-mum density and OMC are known. It is alsoassumed that laboratory-compacted soil andfield-compacted soil are similar and that the

required density can be achieved in the fieldwith the equipment available.

Determination of Moisture ContentIt may be necessary to check the moisture

content of the soil during field rolling for tworeasons. First, since the specified density isin terms of dry unit weight and the densitymeasured directly in the field is generally thewet unit weight, the moisture content mustbe known so that the dry unit weight can becalculated. Second, the moisture content ofsome soils must be maintained close to op-timum if satisfactory densities are to beobtained. Adjustment of the field moisturecontent can only be done if the moisture con-tent is known. The determination of densityand moisture content is often done in oneoverall test procedure; these determinationsare described here separately for con-venience.

Field Examination. Experienced engineerswho have become familiar with the soils en-countered on a particular project canfrequently judge moisture content accuratelyby visual and manual examination. Friableor slightly plastic soils usually containenough moisture at optimum to permit theforming of a strong cast by compressing it inthe hand. As noted, some clay soils haveOMCs that are close to their PLs; thus, a PLor “thread” test conducted in the field may behighly informative.

Field Drying. The moisture content of a soilis best and most accurately determined bydrying the soil in an oven at a controlledtemperature. Methods of determining themoisture content in this fashion are describedin TM 5-530.

The moisture content of the soil may also bedetermined by air drying the soil in the sun.Frequent turning of the soil speeds up thedrying process. From a practical standpoint,this method is generally too slow to be ofmuch value in the control of field rolling.

Several quick methods may be used todetermine approximate moisture contentsunder expedient conditions. For example,

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the sample may be placed in a frying pan anddried over a hot plate or a field stove. Thetemperature is difficult to control in this pro-cedure, and organic materials may be burned,thus causing a slight to moderate error in theresults. On large-scale projects where manysamples are involved, this quick method maybe used to speed up determinations by com-paring the results obtained from this methodwith comparable results obtained by oven-drying.

Another quick method that may be useful isto mix the damp soil with enough denaturedgrain alcohol to form a slurry in a perforatedmetal cup, ignite the alcohol, and permit it toburn off. The alcohol method, if carefullydone, produces results roughly equivalent tothose obtained by careful laboratory drying.For best results, the process of saturating thesoil with alcohol and burning it off completelyshould be repeated three times. This methodis not reliable with clay soils. Safetymeasures must be observed when using thismethod. The burning must be done outside orin a well-ventilated room and at a safe dis-tance from the alcohol supply and otherflammable materials. The metal cup gets ex-tremely hot, arid it should be allowed to coolbefore handling.

“Speedy” Moisture-Content Test. The“speedy” moisture test kit provided with thesoil test set provides a very rapid moisture-content determination and can be highly ac-curate if the test is performed properly. Caremust be exercised to ensure that the reagentused has not lost its strength. The reagentmust be very finely powdered (like portlandcement) and must not have been exposed towater or high humidity before it is used. Thespecific test procedures are contained in thetest set.

Nuclear Denimeter. This device providesreal-time in-place moisture content and den-sity of a soil. Accuracy is high if the test isperformed properly and if the device has beencalibrated with the specific material beingtested. Operators must be certified, andproper safety precautions must be taken to

ensure that the operator does not receive amedically significant dose of radiation duringthe operation of this device. There are strin-gent safety and monitoring procedures thatmust be followed. The method of determiningthe moisture content of a soil in this fashion isdescribed in the operator’s manual.

Determination of Water to Be AddedIf the moisture content of the soil is less

than optimum, the amount of water to beadded for efficient compaction is generallycomputed in gallons per square yards. Thecomputation is based on the dry weight of soilcontained in a compacted layer. For example,assume that the soil is to be placed in 6-inch,compacted layers at a dry weight of 120 pcf.The moisture content of the soil is determinedto be 5 percent while the OMC is 12 percent.Assume that the strip to be compacted is 40feet wide. Compute the amount of water thatmust be added per 100-foot station to bringthe soi1 to optimum moisture. The followingformula applies:

Substituting in the above formula from theconditions given:

If either drying conditions or rain conditionsexist at the time work is in progress, it may beadvisable to either add to or reduce this quan-tity by up to 10 percent.

COMPACTION EQUIPMENTEquipment normally available to the

military engineer for the compaction of soilsincludes the following types of rollers:

Pneumatic-tired.Sheepsfoot.

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Tamping-foot.Smooth steel-wheeled.Vibratory.

Pneumatic-Tired RollerThese heavy pneumatic-tired rollers are

designed so that the weight can be varied toapply the desired compactive effort. Rollerswith capacities up to 50 tons usually have tworows of wheels, each with four wheels andtires designed for 90 psi inflation. They canbe obtained with tires designed for inflationpressures up to 150 psi. As a rule, the higherthe tire pressure the greater the contact pres-sures and, consequently, the greater thecompactive effort obtained. Informationavailable from projects indicates that largerubber-tired compactors are capable of com-pacting clay layers effectively up to about 6inches compacted depth and coarse granularor sand layers slightly deeper. Often it isused especially for final compaction (proofrolling) of the upper 6 inches of subgrade, forsubbases, and for base courses. These rollersare very good for obtaining a high degree ofcompaction. When a large rubber-tired rolleris to be used, care should be exercised to en-sure that the moisture content of cohesivematerials is low enough so that excessive porepressures do not occur. Weaving or springingof the soil under the roller indicates that porepressures are developing.

Since this roller does not aerate the soil asmuch as the sheepsfoot, the moisture contentat the start of compaction should be ap-proximately the optimum. In a soil that hasthe proper moisture content and lift thick-ness, tire contact pressure and the number ofpasses are the important variables affectingthe degree of compaction obtained by rubber-tired rollers. Generally, the tire contactpressure can be assumed to be approximatelyequal to the inflation pressure.

Variants of the pneumatic-tired roller in-clue the pneumatic roller and the self-propelled pneumatic-tired roller.

Pneumatic RollerAs used in this manual, the term “pneu-

matic roller” applies to a small rubber-tired

roller, usually a “wobble wheel. ” Thepneumatic roller is suitable for granularmaterials; however, it is not recommended forfine-grained clay soils except as necessary forsealing the surface after a sheepsfoot rollerhas “walked out. ” It compacts from the topdown and is used for finishing all types ofmaterials, following immediately behind theblade and water truck.

Self-Propelled, Pneumatic-Tired RollerThe self-propelled, pneumatic-tired roller

has nine wheels (see Figure 8-6). It is verymaneuverable, making it excellent for use inconfined spaces. It corn pacts from the topdown. Like the towed models, the self-propelled, pneumatic-tired roller can be usedfor compaction of most soil materials. It isalso suitable for the initial compaction ofbituminous pavement.

For a given number of passes of a rubber-tired roller, higher densities are obtainedwith the higher tire pressures. However, cau-tion and good judgment must be used and thetire pressure adjusted in the field dependingon the nature of the soil being compacted. Forcompaction to occur under a rubber-tiredroller, permanent deformation has to occur.If more than slight pumping or spring occursunder the tires, the roller weight and tirepressure are too high and should be loweredimmediately. Continued rolling under theseconditions causes a decrease in strength eventhough a slight increase in density may occur,For any given tire pressure, the degree of

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compaction increases with additional passes,although the increase may be negligible aftersix to eight passes.

Sheepsfoot RollerThis roller compacts all fine-grained

materials, including materials that will breakdown or degrade under the roller feet, but itwill not compact cohesion less granularmaterials. The number of passes necessaryfor this type of roller to obtain the requireddensities must be determined for each type ofsoil encountered. The roller compacts fromthe bottom up and is used especially for plas-tic materials. The lift thickness forsheepsfoot rollers is limited to 6 inches incompacted depth. Penetration of’ the rollerfeet must be obtained at the start of rollingoperations This roller “walks out” as it com-pletes its compactive effort, leaving the top 1to 2 inches uncompacted.

The roller may tend to “walk out” beforeproper compaction is obtained. To preventthis, the soil may be scarified lightly behindthe roller during the first two or three passes,and additional weight may be added to theroller.

A uniform density can usually be obtainedthroughout the full depth of the lift if thematerial is loose and workable enough toallow the roller feet to penetrate the layer onthe initial passes. This produces compactionfrom the bottom up; therefore, material thatbecomes compacted by the wheels of equip-ment during pulverizing, wetting, blending,and mixing should be thoroughly loosenedbefore compaction operations are begun.This also ensures uniformity of the mixture.The same amount of rolling generallyproduces increased densities as the depth ofthe lift is decreased. If the required densitiesare not being obtained, it is often necessary tochange to a thinner lift to ensure that thespecified density is obtained.

In a soil that has the proper moisture con-tent and lift thickness, foot contact pressureand the number of passes are the importantvariables affecting the degree of compaction

obtained by sheepsfoot rollers. The minimumfoot contact pressure for proper compaction is250 psi. Most available sheepsfoot rollers areequipped with feet having a contact area of 5to 8 square inches. The foot pressure can bechanged by varying the weight of the roller(varying the amount of ballast in the drum),or in special cases, by welding larger platesonto the faces of the feet. For the most effi-cient operation of the roller, the contactpressure should be close to the maximum atwhich the roller will “walk out” satisfactorily,as indicated in Figure 8-7.

The desirable foot contact pressure variesfor different soils, depending on the bearingcapacity of the soil; therefore, the proper ad-justments have to be made in the field basedon observations of the roller. If the feet of theroller tend to “walk out,” too quickly (for ex-ample, after two passes), then bridging mayoccur and the bottom of the lift does not getsufficient compaction. This indicates that theroller is too light or the feet too large, and theweight should be increased. However, if the

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F M 5 - 4 1 0

roller shows no tendency to “walk out” withinthe required number of passes, then the in-dications are that the roller is to (heavy andthe pressure on the roller feet is exceeding thebearing capacity of the soil. After making theproper adjustments in foot pressure (bychangingroller size), the only other variableis the repetition of passes. Tests have shownthat density increases progressively withanincrease in the number of passes.

Tamping-Foot RollerA tamping-foot roller is a modification of

the sheepsfoot roller. The tamping feet aretrapezoidal pads attached to a drum. Tamp-ing-foot rollers are normally self-propelled,and the drum may be capable of vibrating.The tamping-foot roller is suitable for usewith a wide range of soil types.

Steel-Wheeled RollerThe steel-wheeled roller is much less ver-

satile than the pneumatic roller. Althoughextensively used, it is normally operated inconjunction with one of the other three typesof compaction rollers. It is used for compact-ing granular materials in thin lifts. Probablyits most effective use in subgrade work is inthe final finish of a surface. following immedi-ately behind the blade, forming a dense andwatertight surface. Figure 8-8 shows a two-axle tandem (5- to 8-ton) roller.

Self-Propelled, Smooth-DrumVibratory Roller

The self-propelled, smooth-drum vibratoryroller compacts with a vibratory action thatrearranges the soil particles into a densermass (see Figure 8-9). The best results are ob-tained on cohesionless sands arid gravels.Vibratory rollers are relatively light butdevelop high dynamic force through an ec-centric weight arrangement. Compactionefficiency is impacted by the ground speed ofthe roller and the frequency and amplitude ofthe vibrating drum.

Other EquipmentOther construction equipment may be

useful in certain instances, particularly

crawler-type tractor units and loaded haulingunits, including rubber-tired scrapers.Crawler tractors are practical compactingunits, especially for rock and cohesionlessgravels and sands. The material should bespread in thin layers (about 3 or 4 inchesthick) and is usually compacted by vibration.

COMPACTOR SELECTIONTable 8-3, page 8-13, gives information con-

cerning compaction equipment and compactiveefforts recommended for use with each of thegroups of the USCS.

Normally, there is more than one type ofcompactor suitable for use on a project’s

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type(s) of soil. When selecting a compactor,use the following criteria:

Availability.Efficiency.

AvailabilityAscertain the types of compactors that are

available and operationally ready. On majorconstruction projects or when deployed, itmay be necessary to lease compaction equip-ment. The rationale for leasing compactionequipment is based on the role it plays indetermining overall project duration and con-struction quality. Uncompacted lifts cannotbe built on until they are compacted. Sub-stituting less efficient types of compactionequipment decreases productivity and mayreduce project quality if desired dry densitiesare not achieved.

EfficiencyDecide how many passes of each type of

compactor are required to achieve thespecified desired dry density. Determiningthe most efficient compactor is best done on atest strip. A test strip is an area that is locatedadjacent to the project and used to evaluatecompactors and construction procedures. Thecompactive effort of each type of compactorcan be determined on the test strip andplotted graphically. Figure 8-10 compares thefollowing types of compactors:

Vibratory (vibrating drum) roller.Tamping-foot roller.Pneumatic-tired roller.

In this example, a dry density of 129 to 137pcf is desired. The vibrating roller was themost efficient, achieving densities within thespecified density range in three passes. Thetamping foot compactor also compacted thesoil to the desired density in three passes.However, the density achieved (130 pcf) is soclose to the lower limit of the desired densityrange that any variation in the soil may causethe achieved density to drop below 129pcf. The pneumatic-tired roller was theleast efficient and did not densify the soilmaterial to densities within the specifieddensity range.

Once the type(s) of compactor is selected,optimum lift thicknesses can be determined.Table 8-3, page 8-13, provides information onaverage optimum lift thicknesses, but this in-formation must be verified. Again, the teststrip is a way to determine optimum lift thick-ness without interfering with otheroperations occurring on the actual project.

In actual operation, it is likely that more thanone type of compactor will be operating on theproject to maintain peak productivity and tocontinue operations when the primary com-pactors require maintenance or repair. Test-strip data helps to maintain control of projectquality while providing the flexibility to allowconstruction at maximum productivity.

Section IV. Quality Control

PURPOSEPoor construction procedures can in-

validate a good pavement or embankment

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design. Therefore, quality control of construc-tion procedures is as important to the finalproduct as is proper design. The purpose ofquality control is to ensure that the soilis being placed at the proper density andmoisture content to provide adequate bearingstrength (CBR) in the fill. This is ac-complished by taking samples or testing ateach stage of construction. The test resultsare compared to limiting values or specifica-tions, and the compaction should be acceptedor reworked based on the results of the den-sity and moisture content tests. A quality-control plan should be developed for eachproject to ensure that high standards areachieved. For permanent construction, statisti-cal quality-control plans provide the mostreliable check on the quality of compaction.

QUALITY-CONTROL PLANGenerally, a quality-control plan consists of

breaking the total job down into lots with eachlot consisting of “X” units of work. Each lot isconsidered a separate job, and each job will beaccepted or rejected depending on the testresults representing this lot. By handling thecontrol procedure in this way, the project en-gineer is able to determine the quality of thejob on a lot-by-lot basis. This benefits the en-gineering construction unit and projectengineer by identifying the lots that will beaccepted and the lots that will be rejected. Asthis type of information is accumulated fromlot to lot, a better picture of the quality of theentire project is obtained.

The following essential items should beconsidered in a quality-control plan:

Lot size.Random sampling.Test tolerance.Penalty system.

Lot SizeThere are two methods of defining a lot size

(unit of work). A lot size may be defined as anoperational time period or as a quantity ofproduction. One advantage that the quantity-of-production method has over theoperational-time-period method is that theengineering construction unit will probably

have plant and equipment breakdowns andother problems that would require thatproduction be stopped for certain periods oftime. This halt in production could cause dif-ficulties in recording production time. On theother hand, there are always records thatwould show the amount of materials thathave been produced. Therefore, the betterway to describe a lot is to specify that a lot willbe expressed in units of quantity of produc-tion By using this method, each lot willcontain the same amount of materials, estab-lishing each one with the same relativeimportance. Factors such as the size of thejob and the operational capacity usuallygovern the size of a production lot. Typical lotsizes are 2,000 square yards for subbase con-struction and 1,200 square yards forstabilized subgrade construction. To statisti-cally evaluate a lot, at least four samplesshould be obtained and tested properly.

Random SamplingFor a statistical analysis to be acceptable,

the data used for this analysis must be ob-tained from random sampling. Randomsampling means that every sample within thelot has an equal chance of being selected.There are two common types of random sam-pling. One type consists of dividing the lotinto a number of equal size sublets; one ran-dom sample is then taken from each of thesublets. The second method consists of takingthe random samples from the entire lot. Thesublet method has one big advantage, espe-cially when testing during production, in thatthe time between testing is spaced somewhat;when taking random samples from the lot,all tests might occur within a short time.The sublet method is recommended whentaking random samples. It is also recom-mended that all tests be conducted onsamples obtained from in-place material. Byconducting tests in this manner, obtainingadditional samples for testing would not bea problem.

Test ToleranceA specification tolerance for test results

should be developed for various tests with

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consideration given to a tolerance that couldbe met in the field and a tolerance narrowenough so that the quality of the finishedproduct is satisfactory. For instance, thespecifications for a base course would usuallystate that the material must be compacted toat least 100 percent CE 55 maximum density.However, because of natural variation inmaterial, the 100 percent requirement cannotalways be met. Field data indicates that theaverage density is 95 percent and the stand-ard deviation is 3.5. Therefore, it appears thatthe specification should require 95 percentdensity and a standard deviation of 3.5, al-though there is a good possibility that thematerial will further densify under traffic.

Penalty SystemAfter the project is completed, the job

should be rated based on the results of thestatistical quality-control plan for thatproject. A satisfactory job, meeting all of thespecification tolerances, should be considered100 percent satisfactory. On the other hand,those jobs that are not 100 percent satisfac-tory should be rated as such. Any job that iscompletely unsatisfactory should be removedand reconstructed satisfactorily.

THEATER-OF-OPERATIONSQUALITY CONTROL

In the theater of operations, quality controlis usually simplified to a set pattern. This isnot as reliable as statistical testing but is ade-quate for the temporary nature oftheater-of-operations construction. There isno way to ensure that all areas of a project arechecked; however, guidelines for planningquality control are as follows:

Use a “test strip” to determine the ap-proximate number of passes neededto attain proper densities.Test every lift as soon as compactionis completed.Test every roller lane.Test obvious weak spots.Test roads and airfields every 250linear feet, staggering tests about thecenterline.Test parking lots and storage areasevery 250 square yards.

Test trenches every 50 linear feet.Remove all oversized materials.Remove any pockets of organic orunsuitable soil material.Increase the distance between testsas construction progresses, if initialchecks are satisfactory.

CORRECTIVE ACTIONSWhen the density and/or moisture of a soil

does not meet specifications, corrective actionmust be taken. The appropriate correctiveaction depends on the specific problem situa-tion. There are four fundamental problemsituations:

Overcompaction.Undercompaction.Too wet.Too dry.

It is possible to have a situation where oneor more of these problems occur at the sametime, such as when the soil is too dry and alsounder compacted. The specification block thatwas plotted on the moisture density curve(CE 55) is an excellent tool for determining ifa problem exists and what the problem is.

OvercompactionOvercompaction occurs when the material

is densified in excess of the specified densityrange. An overcompacted material may bestronger than required, which indicates—

Wasted construction effort (but notrequiring corrective action to the mate-rial).Sheared material (which no longermeets the design CBR criteria).

In the latter case, scarify the overcompactedlift and recompact to the specified density.Laboratory analysis of overcompacted soils(to include CBR analysis) is required before acorrective action decision can be made.

UndercompactionUndercompaction may indicate—

A missed roller pass.A change in soil type.Insufficient roller weight.

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A change in operating frequency oramplitude (if vibratory rollers are in use).A defective roller drum.The use of an improper type of com-paction equipment.

Corrective action is based on a sequential ap-proach. Initially, apply additional compactiveeffort to the problem area. If undercompact-ing is a frequent problem or develops afrequent pattern, look beyond a missed rollerpass as the cause of the problem.

Too WetSoils that are too wet when compacted are

susceptible to shearing and strength loss,Corrective action for a soil compacted too wetis to—

Scarify.

Aerate.Retest the moisture content.Recompact, if moisture content iswithin the specified range.Retest for both moisture and density.

Too DrySoils that are too dry when compacted do not

achieve the specified degree of densification asdo properly moistened soils. Corrective actionfor a soil compacted too dry is to-

Scarify.Add water.Mix thoroughly.Retest the moisture content.Recompact, if moisture content iswithin the specified range.Retest for both moisture and density.

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CHAPTER 9

S o i l S t a b i l i z a t i o n

f o r R o a d s a n d A i r f i e l d s

Soil stabilization is the alteration of one ormore soil properties, by mechanical or chemi-cal means, to create an improved soil materialpossessing the desired engineering proper-ties. Soils may be stabilized to increasestrength and durability or to prevent erosionand dust generation. Regardless of the pur-pose for stabilization, the desired result is thecreation of a soil material or soil system thatwill remain in place under the design use con-ditions for the design life of the project.

Engineers are responsible for selecting orspecifying the correct stabilizing method,technique, and quantity of material required.This chapter is aimed at helping to make thecorrect decisions. Many of the proceduresoutlined are not precise, but they will “get youin the ball park.” Soils vary throughout theworld, and the engineering properties of soilsare equally variable. The key to success insoil stabilization is soil testing. The methodof soil stabilization selected should be verifiedin the laboratory before construction andpreferably before specifying or orderingmaterials.

Section I. Methods ofStabilization

BASIC CONSIDERATIONSDeciding to stabilize existing soil material

in the theater of operations requires an as-sessment of the mission, enemy, terrain,

troops (and equipment), and time available(METT-T).

Mission. What type of facility is to beconstructed—road, airfield, or build-ing foundation? How long will thefacility be used (design life)?Enemy. Is the enemy interdictinglines of communications? If so, howwill it impact on your ability to haulstabilizing admixtures delivered toyour construction site?Terrain, Assess the effect of terrainon the project during the constructionphase and over the design life of thefacility. Is soil erosion likely? If so,what impact will it have? Is there aslope that is likely to become unstable?Troops (and equipment). Do you haveor can you get equipment needed toperform the stabilization operation?Time available. Does the tactical situa-tion permit the time required to stabi-lize the soil and allow the stabilizedsoil to cure (if necessary)?

There are numerous methods by whichsoils can be stabilized; however, all methodsfall into two broad categories. They are—

Mechanical stabilization.Chemical admixture stabilization.

Some stabilization techniques use a com-bination of these two methods. Mechanical

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stabilization relies on physical processes tostabilize the soil, either altering the physicalcomposition of the soil (soil blending) or plac-ing a barrier in or on the soil to obtain thedesired effect (such as establishing a sodcover to prevent dust generation). Chemicalstabilization relies on the use of an admixtureto alter the chemical properties of the soil toachieve the desired effect (such as using limeto reduce a soil’s plasticity).

Classify the soil material using the USCS.When a soil testing kit is unavailable, classifythe soil using the field identificationmethodology. Mechanical stabilizationthrough soil blending is the most economicaland expedient method of altering the existingmaterial. When soil blending is not feasibleor does not produce a satisfactory soilmaterial, geotextiles or chemical admixturestabilization should be considered. If chemi-cal admixture stabilization is beingconsidered, determine what chemical admix-tures are available for use and any specialequipment or training required to successfullyincorporate the admixture.

MECHANICAL STABILILIZATIONMechanical stabilization produces by com-

paction an interlocking of soil-aggregateparticles. The grading of the soil-aggregatemixture must be such that a dense mass isproduced when it is compacted. Mechanicalstabilization can be accomplished byuniformly mixing the material and then com-pacting the mixture. As an alternative,additional fines or aggregates maybe blendedbefore compaction to form a uniform, well-graded, dense soil-aggregate mixture aftercompaction. The choice of methods should bebased on the gradation of the material. Insome instances, geotextiles can be used to im-prove a soil’s engineering characteristics (seeChapter 11).

The three essentials for obtaining aproperly stabilized soil mixture are—

Proper gradation.A satisfactory binder soil.Proper control of the mixture content.

To obtain uniform bearing capacity, uniformmixture and blending of all materials is es-sential. The mixture will normally becompacted at or near OMC to obtain satisfac-tory densities.

The primary function of the portion of amechanically stabilized soil mixture that isretained on a Number 200 sieve is to con-tribute internal friction. Practically allmaterials of a granular nature that do not sof-ten when wet or pulverize under traffic can beused; however, the best aggregates are thosethat are made up of hard, durable, angularparticles. The gradation of this portion of themixture is important, as the most suitable ag-gregates generally are well-graded fromcoarse to fine. Well-graded mixtures arepreferred because of their greater stabilitywhen compacted and because they can becompacted more easily. They also havegreater increases in stability with cor-responding increases in density. Satisfactorymaterials for this use include—

Crushed stone.Crushed and uncrushed gravel.Sand.Crushed slag.

Many other locally available materialshave been successfully used, including disin-tegrated granite, talus rock, mine tailings,caliche, coral, limerock, tuff, shell, slinkers,cinders, and iron ore. When local materialsare used, proper gradation requirements can-not always be met.

NOTE: If conditions are encountered inwhich the gradation obtained by blend-ing local materials is either finer orcoarser than the specified gradation, thesize requirements of the finer fractionsshould be satisfied and the gradation ofthe coarser sizes should be neglected.

The portion of the soil that passes a Num-ber 200 sieve functions as filler for the rest ofthe mixture and supplies cohesion. This aidsin the retention of stability during dryweather. The swelling of clay material servessomewhat to retard the penetration of

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moisture during wet weather. Clay or dustfrom rock-crushing operations are commonlyused as binders. The nature and amount ofthis finer material must be carefully con-trolled, since too much of it results in an unac-ceptable change in volume with change inmoisture content and other undesirableproperties. The properties of the soil binderare usually controlled by controlling the plas-ticity characteristics, as evidenced by the LLand PI. These tests are performed on the por-tion of the material that passes a Number 40sieve. The amount of fines is controlled bylimiting the amount of material that maypass a Number 200 sieve. When the stabi-lized soil is to be subjected to frost action, thisfactor must be kept in mind when designingthe soil mixture.

UsesMechanical soil stabilization may be used

in preparing soils to function as—Subgrades.Bases.Surfaces.

Several commonly encountered situationsmay be visualized to indicate the usefulnessof this method. One of these situations occurswhen the surface soil is a loose sand that is in-capable of providing support for wheeledvehicles, particularly in dry weather. Ifsuitable binder soil is available in the area, itmay be brought in and mixed in the properproportions with the existing sand to providean expedient all-weather surface for lighttraffic. This would be a sand-clay road. Thisalso may be done in some cases to provide a“working platform” during constructionoperations. A somewhat similar situationmay occur in areas where natural gravelssuitable for the production of a well-gradedsand-aggregate material are not readilyavailable. Crushed stone, slag, or othermaterials may then be stabilized by the addi-tion of suitable clay binder to produce asatisfactory base or surface. A commonmethod of mechanically stabilizing an exist-ing clay soil is to add gravel, sand, or other

granular materials. The objectives here areto—

Increase the drainability of the soil.Increase stability.Reduce volume changes.Control the undeirable effects associatedwith clays.

ObjectiveThe objective of mechanical stabilization is

to blend available soils so that, when properlycompacted, they give the desired stability. Incertain areas, for example, the natural soil ata selected location may have low load-bearingstrength because of an excess of clay, silt, orfine sand. Within a reasonable distance,suitable granular materials may occur thatmay be blended with the existing soils tomarkedly improve the soil at a much lowercost in manpower and materials than is in-volved in applying imported surfacing.

The mechanical stabilization of soils inmilitary construction is very important. Theengineer needs to be aware of the possibilitiesof this type of construction and to understandthe principles of soil action previouslypresented. The engineer must fully inves-tigate the possibilities of using locallyavailable materials.

LimitationsWithout minimizing the importance of

mechanical stabilization, the limitations ofthis method should also be realized. Theprinciples of mechanical stabilization havefrequently been misused, particularly inareas where frost action is a factor in thedesign. For example, clay has been added to“stabilize” soils, when in reality all that wasneeded was adequate compaction to provide astrong, easily drained base that would not besusceptible to detrimental frost action. Anunderstanding of the densification that canbe achieved by modern compaction equip-ment should prevent a mistake of this sort.Somewhat similarly, poor trafficability of asoil during construction because of lack offines should not necessarily provide an excuse

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for mixing in clay binder. The problem maypossibly be solved by applying a thin surfacetreatment or using some other expedientmethod.

Soil Base RequirementsGrading requirements relative to mechani-

cally stabilized soil mixtures that serveas base courses are given in Table 7-3 ofTM 5-330 /Air Force Manual (AFM) 86-3,Volume II. Experience in civil highway con-struction indicates that best results areobtained with this type of mixture if the frac-tion passing the Number 200 sieve is notgreater than two-thirds of the fraction pass-ing the Number 40 sieve. The size of thelargest particles should not exceed two-thirdsof the thickness of the layer in which they areincorporated. The mixture should be well-graded from coarse to fine.

A basic requirement of soil mixtures thatare to be used as base courses is that the PIshould not exceed 5. Under certain cir-cumstances, this requirement may be relaxedif a satisfactory bearing ratio is developed,Experience also indicates that under idealcircumstances the LL should not exceed 25.These requirements may be relaxed intheater-of-operations construction. The re-quirements may be lowered to a LL of 35 anda PI of 10 for fully operational airfields. Foremergency and minimally operational air-fields, the requirements may be lowered to aLL of 45 and a PI of 15, when drainage is good.

Soil Surface RequirementsGrading requirements for mechanically

stabilized soils that are to be used directly assurfaces, usually under emergency condi-tions, are generally the same as those indi-cated in Table 7-3 of TM 5-330/AFM 86-3,Volume II. Preference should be given to mix-tures that have a minimum aggregate sizeequal to 1 inch or perhaps 1 ½ inches. Ex-perience indicates that particles larger thanthis tend to work themselves to the surfaceover a period of time under traffic. Somewhatmore fine soil is desirable in a mixture that isto serve as a surface, as compared with one fora base. This allows the surface to be moreresistant to the abrasive effects of traffic and

penetration of precipitation. To some extent,moisture lost by evaporation can be replacedby capillarity.

Emergency airfields that have surfaces ofthis type require a mixture with a PI between5 and 10. Experience indicates that road sur-faces of this type should be between 4 and 9.The surface should be made as tight as pos-sible, and good surface drainage should beprovided. For best results, the PI of a stabi-lized soil that is to function first as a wearingsurface and then as a base, with a bituminoussurface being provided at a later date, shouldbe held within very narrow limits. Con-sideration relative to compaction, bearingvalue, and frost action are as important forsurfaces of this type as for bases.

ProportioningMixtures of this type are difficult to design

and build satisfactorily without laboratorycontrol. A rough estimate of the properproportions of available soils in the field ispossible and depends on manual and visualinspection. For example, suppose that a loosesand is the existing subgrade soil and it isdesired to add silty clay from a nearby borrowsource to achieve a stabilized mixture. Eachsoil should be moistened to the point where itis moist, but not wet; in a wet soil, the mois-ture can be seen as a shiny film on the surface,What is desired is a mixture that feels grittyand in which the sand grains can be seen.Also, when the soils are combined in theproper proportion, a cast formed by squeezingthe moist soil mixture in the hand will not beeither too strong or too weak; it should just beable to withstand normal handling withoutbreaking. Several trial mixtures should bemade until this consistency is obtained. Theproportion of each of the two soils should becarefully noted. If gravel is available, thismay be added, although there is no real rule ofthumb to tell how much should be added. It isbetter to have too much gravel than too little.

Use of Local Materials. The essence ofmechanical soil stabilization is the use of lo-cally available materials. Desirable require-ments for bases and surfaces of this type weregiven previously. It is possible, especiallyunder emergency conditions, that mixtures of

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local materials will give satisfactory service,even though they do not meet the stated re-quirements. Many stabilized mixtures havebeen made using shell, coral, soft limestone,cinders, marl, and other materials listed ear-lier. Reliance must be placed on—

Experience.An understanding of soil action.The qualities that are desired in thefinished product.Other factors of local importance inproportioning such mixtures in thefield.

Blending. It is assumed in this discussionthat an existing subgrade soil is to be stabi-lized by adding a suitable borrow soil toproduce a base course mixture that meets thespecified requirements. The mechanicalanalysis and limits of the existing soil willusually be available for the results of the sub-grade soil survey (see Chapter 3). Similarinformation is necessary concerning the bor-row soil. The problem is to determine theproportions of these two materials thatshould be used to produce a satisfactory mix-ture. In some cases, more than two soils mustbe blended to produce a suitable mixture.However, this situation is to be avoided whenpossible because of the difficulties frequentlyencountered in getting a uniform blend ofmore than two local materials. Trial com-binations are usually made on the basis of themechanical analysis of the soil concerned. Inother words, calculations are made to deter-mine the gradation of the combined materialsand the proportion of each component ad-justed so that the gradation of thecombination falls within specified limits. ThePI of the selected combination is then deter-mined and compared with the specification.If this value is satisfactory, then the blendmay be assumed to be satisfactory, providedthat the desired bearing value is attained. Ifthe plasticity characteristics of the first comb-ination are not within the specified limits,additional trials must be made. The propor-tions finally selected then may be used in thefield construction process.

Numerical Proportioning. The process ofproportioning will now be illustrated by a

numerical example (see Table 9-1, page 9-6).Two materials are available, material B in theroadbed and material A from a nearby borrowsource. The mechanical analysis of each ofthese materials is given, together with the LLand PI of each. The desired grading of thecombination is also shown, together with thedesired plasticity characteristics.

Specified Gradation. Proportioning oftrial combinations may be done arithmetical-ly or graphically. The first step in usingeither the graphical or arithmetical method isto determine the gradation requirements.Gradation requirements for base course, sub-course, and select material are found inTables 7-1 and 7-3, TM 5-330/AFM 86-3,Volume II. In the examples in Figures 9-1and 9-2, page 9-7, abase course material witha maximum aggregate size of 1 inch has beenspecified. In the graphical method, thegradation requirements are plotted to theoutside of the right axis. In the arithmeticalmethod, they are plotted in the columnlabelled “Specs.” Then the gradations of thesoils to be blended are recorded. The graphi-cal method has the limitation of only beingcapable of blending two soils, whereas thearithmetical method can be expanded toblend as many soils as required. At this point,the proportioning methods are distinctiveenough to require separate discussion.

Graphical Proportioning. The actualgradations of soil materials A and B areplotted along the left and right axes of thegraph, respectively. As shown in Figure 9-1,page 9-7, material A has 92 percent passingthe 3/4-inch sieve while material B has 72percent passing the same sieve. Once plotted,a line is drawn across the graph, connectingthe percent passing of material A with thepercent passing of material B for each sievesize.

NOTE: Since both materials A and B had100 percent passing the l-inch sieve, itwas omitted from the graph and willnot affect the results.

Mark the point where the upper and lowerlimits of the gradation requirements intersect

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the line for each sieve size. In Figure 9-1, theallowable percent passing the Number 4 sieveranges from 35 to 65 percent passing. Thepoint along the Number 4 line at which 65percent passing intersects represents 82 per-cent material A and 18 percent material B.The 35 percent passing intersects the Num-ber 4 line at 19 percent material A and 81percent material B. The acceptable ranges ofmaterial A to be blended with material B isthe widest range that meets the gradation re-quirements for all sieve sizes. The shadedarea of the chart represents the combinationsof the two materials that will meet thespecified gradation requirements. Theboundary on the left represents the combina-tion of 44 percent material A and 56 percentmaterial B. The position of this line is fixedby the upper limit of the requirement relatingto the material passing the Number 200 sieve(15 percent). The boundary on the right rep-resents the combination of 21 percentmaterial A and 79 percent material B. Thisline is established by the lower limit of the re-quirement relative to the fraction passing theNumber 40 sieve (15 percent). Any mixturefalling within these limits satisfies the grada-tion requirements. For purposes ofillustration, assume that a combination of 30percent material A and 70 percent material

B is selected for a trial mixture, A similardiagram can be prepared for any two soils.

Arithmetical Proportioning. Record theactual gradation of soils A and B in theirrespective columns (Columns 1 and 2, Figure9-2). Average the gradation limits and recordin the column labelled "S". For example, theallowable range for percent passing a 3/8-inchsieve in a 1-inch minus base course is 50 to 80percent. The average, 50±80/2, is 65 percent.As shown in Figure 9-2, S for 3/8 inch is 65.Next, determine the absolute value of S-Aand S-B for each sieve size and record in thecolumns labelled “ (S-A)“ and “ (S-B), res-pectively. Sum columns (S-A) and ( S-B).To determine the percent of soil A in the finalmix, use the formula—

In the example in Figure 9-2:

103 103134 + 103 x 100% = 43.5%= 2 3 7

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The percent of soil B in the final mix can bedetermined by the formula:

or

100% - %A = %B

NOTE: If three or more soils are to beblended, the formula would be—

%C =

This formula can be further expanded asnecessary.

Multiply the percent passing each sieve forsoil A by the percentage of soil A in the finalmix; record the information in column 4 (seeFigure 9-2, page 9-7), Repeat the procedurefor soil B and record the information incolumn 5 (see Figure 9-2, page 9- 7). Completethe arithmetical procedure by addingcolumns 4 and 5 to obtain the percent passingeach sieve in the blended soil.

Both the graphical and arithmeticalmethods have advantages and disad-vantages. The graphical method eliminatesthe need for precise blending under field con-ditions and the methodology requires lesseffort to use, Its drawback becomes very com-plex when blending more than two soils. Thearithmetical method allows for more preciseblending, such as mixing at a batch plant, andit can be readily expanded to accommodatethe blending of three or more soils. It has thedrawback in that precise blending is often un-attainable under field conditions. Thisreduces the quality assurance of the perfor-mance of the blended soil material.

Plasticity Requirements. A method ofdetermining the PI and LL of the combinedsoils serves as a method to indicate if theproposed trial mixture is satisfactory, pend-ing the performance of laboratory tests. Thismay be done either arithmetically or graphi-cally. A graphical method of obtaining these

Soil Stabilization for Roads and Airfields 9-8

approximate values is shown in Figure 9-3.The values shown in Figure 9-3 require addi-tional explanation, as follows. Consider 500pounds of the mixture tentatively selected (30percent as material A and 70 percent asmaterial B). Of this 500 pounds, 150 poundsare material A and 350 pounds material B.Within the 150 pounds of material A, thereare 150 (0.52) = 78 pounds of material passingthe Number 40 sieve. Within the 350 poundsof material B, there are 150 (0.05) = 17.5pounds of material passing the Number 40sieve. The total amount of material passingthe Number 40 sieve in the 500 pounds ofblend = 78+ 17.5= 95.5 pounds, The percent-age of this material that has a PI of 9(material A) is (78/95.5) 100= 82. As shown inFigure 9-3, the approximate PI of the mixtureof 30 percent material A and 70 percentmaterial B is 7.4 percent. By similar reason-ing, the approximate LL of the blend is 28,4percent. These values are somewhat higherthan permissible under the specification. Anincrease in the amount of material B willsomewhat reduce the PI and LL of the com-bination.

Field Proportioning. In the field, thematerials used in a mechanically stabilizedsoil mixture probably will be proportioned byloose volume. Assume that a mixture incor-porates 75 percent of the existing subgradesoil, while 25 percent will be brought in froma nearby borrow source. The goal is to con-struct a layer that has a compacted thicknessof 6 inches. It is estimated that a loose thick-ness of 8 inches will be required to form the6-inch compacted layer. A more exactrelationship can be established in the field asconstruction proceeds, Of the 8 inches loosethickness, 75 percent (or 0.75(8) = 6 inches)will be the existing soil, The remainder of themix will be mixed thoroughly to a depth of8 inches and compacted by rolling. Theproportions may be more accurately control-led by weight, if weight measurements can bemade under existing conditions.

WaterproofingThe ability of an airfield or road to sustain

operations depends on the bearing strength ofthe soil. Although an unsurfaced facility maypossess the required strength when initiallyconstructed, exposure to water can result i n a

FM 5-410

loss of strength due to the detrimental effectof traffic operations. Fine-grained soils orgranular materials that contain an excessiveamount of fines generally are more sensitiveto water changes than coarse-grained soils.Surface water also may contribute to thedevelopment of dust by eroding or looseningmaterial from the ground surface that can be-come dust during dry weather conditions.

Sources of Water. Water may enter a soileither by the percolation of precipitation orponded surface water, by capillary action ofunderlying ground water, by a rise in thewater-table level, or by condensation of watervapor and accumulation of moisture under avapor-impermeable surface. As a generalrule, an existing groundwater table at shal-low depths creates a low load-bearingstrength and must be avoided wherever pos-sible. Methods to protect against moistureingress from sources other than the groundsurface will not be considered here. In mostinstances, the problem of surface water can belessened considerably by following the properprocedures for—

Grading.

Compaction.Drainage.

Objectives of Waterproofers. The objec-tive of a soil-surface waterproofer is to protecta soil against attack by water and thuspreserve its in-place or as-constructedstrength during wet-weather operations.The use of soil waterproofers generally islimited to traffic areas. In some instances,soil waterproofers may be used to prevent ex-cessive softening of areas, such as shouldersor overruns, normally considered nontrafficor limited traffic areas.

Also, soil waterproofers may prevent soilerosion resulting from surface water runoff.As in the case of dust palliative, a thin orshallow-depth soil waterproofing treatmentloses its effectiveness when damaged by ex-cessive rutting and thus can be usedefficiently only in areas that are initially firm.Many soil waterproofers also function well asdust palliatives; therefore, a single materialmight be considered as a treatment in areaswhere the climate results in both wet and drysoil surface conditions. Geotextiles are the

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primary means of waterproofing soils whengrading, compaction, and drainage practicesare insufficient. Use of geotextiles is dis-cussed in detail in Chapter 11.

CHEMICAL ADMIXTURE STABILIZATIONChemical admixtures are often used to sta-

bilize soils when mechanical methods ofstabilization are inadequate and replacing anundesirable soil with a desirable soil is notpossible or is too costly. Over 90 percent of allchemical admixture stabilization projectsuse—

Cement.Lime.Fly ash.Bituminous materials.

Other stabilizing chemical admixtures areavailable, but they are not discussed in thismanual because they are unlikely to be avail-able in the theater of operations.

WARNINGChemical admixtures may contain haz-ardous materials, Consult Appendix Cto determine the necessary safetyprecautions for the selected admixture.

When selecting a stabilizer additive, thefactors that must be considered are the—

Type of soil to be stabilized.Purpose for which the stabilized layerwill be used.Type of soil quality improvementdesired.Required strength and durability ofthe stabilized layer.Cost and environmental conditions.

Table 9-2 lists stabilization methods mostsuitable for specific applications. To deter-mine the stabilizing agent(s) most suited to aparticular soil, use the gradation triangle inFigure 9-4, page 9-12, to find the area that cor-responds to the gravel, sand, and fine contentof the soil. For example, soil D has the follow-ing characteristics:

With 95 percent passing the Numbersieve, the PI is 14.With 14 percent passing the Number200 sieve, the LL is 21.

Therefore the soil is 5 percent gravel, 81percent sand, and 14 percent fines. Figure9-4, page 9-12, shows this soil in Area 1C.

Table 9-3, page 9-13, shows that thestabilizing agents recommended for Area 1Csoils include bituminous material, portlandcement, lime, and lime-cement-fly ash. Inthis example, bituminous agents cannot beused because of the restriction on PI, but anyof the other agents can be used if available.

CementCement can be used as an effective stabi-

lizer for a wide range of materials. In general,however, the soil should have a PI less than30. For coarse-grained soils, the percentpassing the Number 4 sieve should be greaterthan 45 percent.

If the soil temperature is less than 40degrees Fahrenheit and is not expected to in-crease for one month, chemical reactions willnot occur rapidly. The strength gain of the ce-ment-soil mixture will be minimal. If theseenvironmental conditions are anticipated,the cement may be expected to act as a soilmodifier, and another stabilizer might be con-sidered for use. Soil-cement mixtures shouldbe scheduled for construction so that suffi-cient durability will be gained to resist anyfreeze-thaw cycles expected.

Portland cement can be used either tomodify and improve the quality of the soil orto transform the soil into a cemented mass,which significantly increases its strength anddurability. The amount of cement additivedepends on whether the soil is to be modifiedor stabilized. The only limitation to theamount of cement to be used to stabilize ormodify a soil pertains to the treatment of thebase courses to be used in flexible pavementsystems. When a cement-treated base coursefor Air Force pavements is to be surfaced with

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asphaltic concrete, the percent of cement by find the design cement content based on totalweight is limited to 4 percent. sample weight expressed as—

Modification. The amount of cement re- A = 100Bcquired to improve the quality of the soilthrough modification is determined by the where—trial-and-error approach. To reduce the PI ofthe soil, successive samples of soil-cement A=mixtures must be prepared at different treat-ment levels and the PI of each mixturedetermined. B=

The minimum cement content that yieldsthe desired PI is selected, but since it was c =determined based on the minus 40 fraction ofthe material, this value must be adjusted to

design cement content, percent oftotal weight of soil

percent passing Number 40 sieve, expressed as a decimal

percent of cement required to obtainthe desired PI of minus Number 40material, expressed as a decimal

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If the objective of modification is to im-prove the gradation of granular soil throughthe addition of fines, the analysis should beconducted on samples at various treatmentlevels to determine the minimum acceptablecement content. To determine the cementcontent to reduce the swell potential of fine-grained plastic soils, mold several samples atvarious cement contents and soak thespecimens along with untreated specimensfor four days. The lowest cement content thateliminates the swell potential or reducesthe swell characteristics to the minimum

becomes the design cement content. The ce-ment content determined to accomplish soilmodification should be checked to see if itprovides an unconfined compressive strengthgreat enough to qualify for a reduced thick-ness design according to criteria establishedfor soil stabilization (see Tables 9-4 and 9-5,page 9-14).

Cement-modified soil may be used in frostareas also. In addition to the procedures forthe mixture design described above, curedspecimens should be subjected to the 12

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freeze-thaw cycles test (omit wire brush por-tion) or other applicable freeze-thaw pro-cedures. This should be followed by a frost-susceptibility test, determined after freeze-thaw cycling, and should meet the require-ments set forth for the base course. If cement-modified soil is used as the subgrade, its frostsusceptibility (determined after freeze-thawcycling) should be used as the basis of thepavement thickness design if the reducedsubgrade-strength design method is applied.

Stabilization. The following procedure isrecommended for determining the design ce-ment content for cement-stabilized soils:

Step 1. Determine the classificationand gradation of the untreated soil.The soil must meet the gradation re-quirements shown in Table 9-6 beforeit can be used in a reduced thicknessdesign (multilayer design).

Step 2. Select an estimated cementcontent from Table 9-7 using the soilclassification.

Step 3. Using the estimated cementcontent, determine the compactioncurve of the soil-cement mixture.

Step 4. If the estimated cement con-tent from step 2 varies by more than±2 percent from the value in Tables9-8 or 9-9, page 9-16, conductadditional compaction tests, varyingthe cement content, until the valuefrom Table 9-8 or 9-9, page 9-16, iswithin 2 percent of that used for themoisture-density test.

NOTE: Figure 9-5, page 9-17, is used inconjunction with Table 9-9, page 9-16.The group index is obtained from Fig-ure 9-5, page 9-17 and used to enterTable 9-9, page 9-16.

Step 5. Prepare samples of the soil-cement mixture for unconfined com-pression and durability tests at the drydensity and at the cement contentdetermined in step 4. Also preparesamples at cement contents 2 percentabove and 2 percent below thatdetermined in step 4. The samplesshould be prepared according toTM 5-530 except that when morethan 35 percent of the material isretained on the Number 4 sieve,

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a CBR mold should be used toprepare the specimens. Cure thespecimens for seven days in a humidroom before testing. Test three spec-imens using the unconfined com-pression test and subject three spec-imens to durability tests. These testsshould be either wet-dry tests forpavements located in nonfrost areasor freeze-thaw tests for pavementslocated in frost areas.

Step 6. Compare the results of theunconfined compressive strength anddurability tests with the require-ments shown in Tables 9-4 and 9-5.

The lowest cement content thatmeets the required unconfined com-pressive strength requirementand demonstrates the requireddurability is the design content.If the mixture should meet thedurability requirements but notthe strength requirements, themixture is considered to be amodified soil.

Theater-of-operations construction re-quires that the engineer make maximum useof the locally available constructionmaterials. However, locally availablematerials may not lend themselves to

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classification under the USCS method. Theaverage cement requirements of common lo-cally available construction materials isshown in Table 9-10.

LimeExperience has shown that lime reacts with

medium-, moderately fine-, and fine-grainedsoils to produce decreased plasticity, in-creased workability and strength, andreduced swell. Soils classified according tothe USCS as (CH), (CL), (MH), (ML), (SC),(SM), (GC), (GM), (SW-SC), (SP-SC), (SM-SC), (GW-GC), (GP-GC), and (GM-GC)should be considered as potentially capable ofbeing stabilized with lime.

If the soil temperature is less than 60degrees Fahrenheit and is not expected to in-crease for one month, chemical reactions willnot occur rapidly. Thus, the strength gain ofthe lime-soil mixture will be minimal. Ifthese environmental conditions are expected,the lime may be expected to act as a soilmodifier. A possible alternative stabilizermight be considered for use. Lime-soil mix-tures should be scheduled for construction sothat sufficient durability is gained to resistany freeze-thaw cycles expected.

If heavy vehicles are allowed on the lime-stabilized soil before a 10- to 14-day curingperiod, pavement damage can be expected.Lime gains strength slowly and requiresabout 14 days in hot weather and 28 days incool weather to gain significant strength. Un-surfaced lime-stabilized soils abrade rapidlyunder traffic, so bituminous surface treat-ment is recommended to prevent surfacedeterioration.

Lime can be used either to modify some ofthe physical properties and thereby improvethe quality of a soil or to transform the soilinto a stabilized mass, which increases itsstrength and durability. The amount of limeadditive depends on whether the soil is to re-modified or stabilized. The lime to be usedmay be either hydrated or quicklime, al-though most stabilization is done usinghydrated lime. The reason is that quicklimeis highly caustic and dangerous to use. Thedesign lime contents determined from thecriteria presented herein are for hydratedlime. As a guide, the lime contents deter-mined herein for hydrated lime should bereduced by 25 percent to determine a designcontent for quicklime.

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Modification. The amount of lime requiredto improve the quality of a soil is determinedthrough the same trial-and-error processused for cement-modified soils.

Stabilization. To take advantage of thethickness reduction criteria, the lime-stabi-lized soil must meet the unconfinedcompressive strengths and durability re-quirements shown in Tables 9-4 and 9-5, page9-14, respectively.

When lime is added to a soil, a com-bination of reactions begins to take placeimmediately. These reactions are nearly com-plete within one hour, althoughsubstantial strength gain is not reflectedfor some time. The reactions result in achange in both the chemical compositionand the physical properties. Most lime hasa pH of about 12.4 when placed in awater solution. Therefore, the pH is a goodindicator of the desirable lime content of asoil-lime mixture. The reaction that takesplace when lime is introduced to a soilgenerally causes a significant change in theplasticity of the soil, so the changes in thePL and the LL also become indicators ofthe desired lime content. Two methods fordetermination of the initial design limecontent are presented in the following steps:

Step 1. The preferred method is toprepare several mixtures at differentlime-treatment levels and determinethe pH of each mixture after onehour. The lowest lime content pro-ducing the highest pH of the soil-limemixtures is the initial design limecontent. Procedures for conducting apH test on lime-soil mixtures arepresented in TM 5-530. In frost areas,specimens must be subjected to thefreeze-thaw test as discussed in step 2below. An alternate method of deter-mining an initial design lime contentis shown in Figure 9-6, page 9-20.Specific values required to use thisfigure are the PI and the percent ofmaterial passing the Number 40 sieve.These properties are determined fromthe PL and the gradation test on the

untreated soil for expedient construc-tion; use the amount of stabilizer deter-mined from the pH test or Figure 9-6,page 9-20.

Step 2. After estimating the initiallime content, conduct a compactiontest with the lime-soil mixture. Thetest should follow the same pro-cedures for soil-cement except themixture should cure no less than onehour and no more than two hours in asealed container before molding.Compaction will be accomplished infive layers using 55 blows of a10-pound hammer having an 18-inchdrop (CF 55). The moisture densityshould be determined at lime con-tents equal to design plus 2 percentand design plus 4 percent for thepreferred method at design ± 2 per-cent for the alternate method, Infrost areas, cured specimens shouldbe subjected to the 12 freeze-thawcycles (omit wire brush portion) orother applicable freeze-thaw pro-cedures, followed by frost sus-ceptibility determinations in stan-dard laboratory freezing tests.For lime-stabilized or lime-modifiedsoil used in lower layers of the basecourse, the frost susceptibility (deter-mined after freeze-thaw cycling)should meet the requirements for thebase course. If lime-stabilized or lime-modified soil is used as the subgrade,its frost susceptibility (determinedafter freeze-thaw cycling) should bethe basis of the pavement thicknessdesign if the reduced subgrade strengthdesign method is applied.

Step 3. Uniformed compression testsshould be performed it the designpercent of maximum density on threespecimens for each lime contenttested. The design value would thenbe the minimum lime content yieldingthe required strength. Procedures forthe preparation of lime-soil specimensare similar to those used for cement-stabilized soils with two exceptions:

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I

Soil Stabilization for Roads and AirfieIds 9-20

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after mixing, the lime-soil mixtureshould be allowed to mellow for notless than one hour nor more than twohours; after compaction, each spec-imen should be wrapped securely toprevent moisture loss and should becured in a constant-temperature cham-ber at 73 degrees Fahrenheit ±2degrees Fahrenheit for 28 days. Pro-cedures for conducting unconfinedcompression tests are similar to thoseused for soil-cement specimens exceptthat in lieu of moist curing, the lime-soil specimens should remain securelywrapped until testing.

Step 4. Compare the results of theunconfined compressive tests with thecriteria in Table 9-4, page 9-14. Thedesign lime content must be the low-est lime content of specimens meetingthe strength criteria indicated.

Other Additives. Lime may be used as apreliminary additive to reduce the PI or altergradation of a soil before adding the primarystabilizing agent (such as bitumen or ce-ment). If this is the case, then the design limecontent is the minimum treatment level thatwill achieve the desired results. For nonplas-tic and low-PI materials in which lime alonegenerally is not satisfactory for stabilization,fly ash may be added to produce the necessaryreaction.

Fly AshFly ash is a pozzolanic material that con-

sists mainly of silicon and aluminumcompounds that, when mixed with lime andwater, forms a hardened cementitious masscapable of obtaining high compressionstrengths. Fly ash is a by-product of coal-fired, electric power-generation facilities.The liming quality of fly ash is highly depend-ent on the type of coal used in powergeneration. Fly ash is categorized into twobroad classes by its calcium oxide (CaO) con-tent. They are—

Class C.Class F.

Class C. This class of fly ash has a high CaOcontent (12 percent or more) and originatesfrom subbituminous and lignite (soft) coal.Fly ash from lignite has the highest CaO con-tent, often exceeding 30 percent. This typecan be used as a stand-alone stabilizingagent. The strength characteristics of ClassC fly ash having a CaO less than 25 percentcan be improved by adding lime. Further dis-cussion of fly ash properties and a listing ofgeographic locations where fly ash is likely tobe found are in Appendix B.

Class F. This class of fly ash has a low CaOcontent (less than 10 percent) and originatesfrom anthracite and bituminous coal. Class Ffly ash has an insufficient CaO content for thepozzolanic reaction to occur. It is not effectiveas a stabilizing agent by itself; however, whenmixed with either lime or lime and cement,the fly ash mixture becomes an effectivestabilizing agent.

Lime Fly Ash Mixtures. LF mixtures cancontain either Class C or Class F fly ash. TheLF design process is a four-part process thatrequires laboratory analysis to determine theoptimum fines content and lime-to-fly-ashratio.

Step 1. Determine the optimum finescontent. This is the percentage of flyash that results in the maximum den-sity of the soil mix. Do this by con-ducting a series of moisture-densitytests using different percentages offly ash and then determining the mixlevel that yields maximum density.The initial fly ash content should beabout 10 percent based on the weightof the total mix. Prepare test samplesat increasing increments (2 percent)of fly ash, up to 20 percent. Thedesign fines content should be 2 per-cent above the optimum fines content.For example, if 14 percent fly ashyields the maximum density, thedesign fines content would be 16 per-cent. The moisture density relationwould be based on the 16 percentmixture.

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Step 2. Determine the rates of lime tofly ash, Using the design fines con-tent and the OMC determined in step1, prepare triplicate test samples atLF ratios of 1:3, 1:4, and 1:5. Cure alltest samples in sealed containers forseven days at 100 degrees Fahrenh-eit .

Step3. Evaluate the test samples forunconfined compressive strength. Iffrost is a consideration, subject a setof test samples to 12 cycles of freeze-thaw durability tests (refer to FM5-530 for actual test procedures).

Step 4. Determine the design LFratio. Compare the results of theunconfined strength test andfreeze-thaw durability tests with theminimum requirements found inTables 9-4 and 9-5, page 9-14,respectively. The LF ratio with thelowest lime content that meets therequired unconfined compressivestrength and demonstrates therequired durability is the design LFcontent. The treated material must alsomeet frost susceptibility requirementsas indicated in Special Report 83-27. Ifthe mixture meets the durabilityrequirements but not the strengthrequirements, it is considered to be amodified soil. If neither strength nordurability criteria are met, a differentLF content may be selected and thetesting procedure repeated.

Lime-Cement-Fly Ash (LCF) Mixtures.The design methodology for determining theLCF ratio for deliberate construction is thesame as for LF except cement is added in step2 at the ratio of 1 to 2 percent of the designfines content. Cement may be used in place ofor in addition to lime; however, the designfines content should be maintained.

When expedient construction is required,use an initial mix proportion of 1 percentportland cement, 4 percent lime, 16 per-cent fly ash, and 79 percent soil. Minimum

unconfined strength requirements (seeTable 9-4, page 9-14) must be met. If testspecimens do not meet strength require-ments, add cement in 1/2 percent incrementsuntil strength is adequate. In frost-suscep-tible areas, durability requirements mustalso be satisfied (see Table 9-5, page 9-14).

As with cement-stabilized base coursematerials, LCF mixtures containing morethan 4 percent cement cannot be used as basecourse material under Air Force airfield pave-ments.

Bituminous MaterialsTypes of bituminous-stabilized soils are—

Soil bitumen. A cohesive soil systemmade water-resistant by admixture.Sand bitumen. A system in whichsand is cemented together by bitumi-nous material.Oiled earth. An earth-road systemmade resistant to water absorptionand abrasion by means of a sprayedapplication of slow- or medium-curingliquid asphalt.Bitumen-waterproofed, mechanicallystabilized soil. A system in which twoor more soil materials are blended toproduce a good gradation of particlesfrom coarse to fine. Comparativelysmall amounts of bitumen are needed,and the soil is compacted.Bitumen-lime blend. A system in whichsmall percentages of lime are blendedwith fine-grained soils to facilitate thepenetration and mixing of bitumensinto the soil.

Soil Gradation. The recommended soilgradations for subgrade materials and baseor subbase course materials are shown inTables 9-11 and 9-12, respectively. Mechani-cal stabilization may be required to bring soilto proper gradation.

Types of Bitumen. Bituminous stabiliza-tion is generally accomplished using—

Asphalt cement.Cutback asphalt.Asphalt emulsions.

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The type of bitumen to be used depends on- -the type of soil to be stabilized, the method ofconstruction, and the weather conditions. Infrost areas, the use of tar as a binder should beavoided because of its high-temperature sus-ceptibility. Asphalts are affected to a lesserextent by temperature changes, but a grade ofasphalt suitable to the prevailing climateshould be selected. Generally the most satis-factory results are obtained when the mostviscous liquid asphalt that can be readilymixed into the soil is used. For higher qualitymixes in which a central plant is used,viscosity-grade asphalt cements should beused. Much bituminous stabilization is per-formed in place with the bitumen beingapplied directly on the soil or soil-aggregatesystem. The mixing and compaction opera-tions are conducted immediately thereafter.For this type of construction, liquid asphalts(cutbacks and emulsions) are used. Emul-sions are preferred over cutbacks because ofenergy constraints and pollution control ef-fects. The specific type and grade of bitumendepends on the characteristics of the ag-gregate, the type of construction equipment,and the climatic conditions. Table 9-13, page9-24, lists the types of bituminous materialsfor use with soils having different gradations.

Mix Design. Guidance for the design ofbituminous-stabilized base and subbase cour-ses is contained in TM 5-822-8. For subgradestabilization, the following equation may beused for estimating the preliminary quantityof cutback asphalt to be selected:

P =

where—

P =

a =

b =

c=

d=

S=

percent of cutback asphalt by weightof dry aggregate

percent of mineral aggregate retainedon Number 50 sieve

percent of mineral aggregate passingNumber 50 and retained onNumber 100 sieve

percent of mineral aggregate passingNumber 100 and retained onNumber 200 sieve

percent of mineralNumber 200 sieve

percent solvent

aggregate passing

The preliminary quantity of emulsified as-phalt to be used in stabilizing subgrades canbe determined from Table 9-14, page 9-24.Either cationic or anionic emulsions can beused. To ascertain which type of emulsion is

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Soil Stabilization for Roads and Airfields 9-25

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preferred, first determine the general type ofaggregate. If the aggregate contains a highcontent of silica, as shown in Figure 9-7, page9-25, a cationic emulsion should be used (seeFigure 9-8, page 9-25.). If the aggregate is acarbonate rock (limestone, for example), ananionic emulsion should be used.

Figures 9-9 and 9-10 can be used to find themix design for asphalt cement. Thesepreliminary quantities are used for expedientconstruction. The final design content of as-phalt should be selected based on the resultsof the Marshall stability test procedure. Theminimum Marshall stability recommendedfor subgrades is 500 pounds; for base courses,750 pounds is recommended. If a soil does notshow increased stability when reasonableamounts of bituminous materials are added,the gradation of the soil should be modified oranother type of bituminous material shouldbe used. Poorly graded materials may be

improved by adding suitable fines containingconsiderable material passing a Number 200sieve. The amount of bitumen required for agiven soil increases with an increase in per-centage of the finer sizes.

Section II. Design ConceptsSTRUCTURAL CATEGORIES

Procedures are presented for determiningdesign thicknesses for two structuralcategories of pavement. They are—

Single-layer.Multilayer.

Typical examples of these pavements are in-dicated in Figure 9-11.

A typical single-layer pavement is a stabi-lized soil structure on a natural subgrade.The stabilized layer may be mixed in place orpremixed and later placed over the existingsubgrade. A waterproofing surface such asmembrane or a single bituminous surface(SBST) or a double bituminous surface treat-ment (DBST) may also be provided. Amultilayer structure typically consists of atleast two layers, such as a base and a wearingcourse, or three layers, such as a subbase, abase, and a wearing course. A thinwaterproofing course may also be used onthese structures. Single-layer and multi-layer pavement design procedures arepresented for all categories of roads and forcertain categories of airfields as indicated inTable 9-15, page 9-28.

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Both single-layer and multilayer pavementstructures may be constructed under eitherthe expedient or nonexpedient concept. Dif-ferent structural designs are provided toallow the design engineer wider latitude ofchoice. However, single-layer structures areoften associated with expedient constructionrather than nonexpedient construction, andmulti layers are nonexpedient and per-manent. Certain considerations should bestudied to determine whether to use a single-layer or mulilayer design under eitherconcept.

The overall concept of design as describedherein can be defined in four basic determina-tions as indicated in Table 9-16.

STABILIZED PAVEMENTDESIGN PROCEDURE

To use different stabilized materials effec-tively in transportation facilities, the designprocedure must incorporate the advantagesof the higher quality materials. These ad-vantages are usually reflected in betterperformance of the structures and a reductionin total thicknesses required. From astandpoint of soil stabilization (not modifica-tion), recent comparisons of behavior basedon type and quality of material have shownthat stabilization provides definite structuralbenefits. Design results for airfield and road

Soil Stabilization for Roads and Airfields 9-28

classifications are presented to provideguidance to the designer in determiningthickness requirements when using stabi-lized soil elements. The design thickness alsoprovides the planner the option of comparingthe costs of available types of pavement con-struction, thereby providing the beststructure for the situation.

The design procedure primarily incorporatesthe soil stabilizers to allow a reduction ofthickness from the conventional flexiblepavement-design thicknesses. These thick-ness reductions depend on the properconsideration of the following variables:

Load.Tire pressure.Design life.Soil properties.Soil strength.Stabilizer type.Environmental conditions.Other factors.

The design curves for theater-of-operationsairfields and roads are given for single-layerand multi layer pavements later in this sec-tion.

In the final analysis, the choice of the ad-mixture to be used depends on the economics

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and availability of the materials involved.The first decision that should be made iswhether stabilization should be attemptedat all. In some cases, it may be economicalmerely to increase the compaction require-ments or, as a minimum, to resort toincreased pavement thickness. If locallyavailable borderline or unacceptablematerials are encountered, definite con-sideration should be given to upgrading anotherwise unacceptable soil by stabilization.

The rapid method of mix design should beindicative of the type and percentage of stabi-lizer required and the required designthickness. This procedure is meant to be afirst-step type of approach and is by no meansconclusive. Better laboratory tests areneeded to evaluate strength and durabilityand should be performed in specific caseswhere time allows. Estimated time require-ments for conducting tests on stabilizedmaterial are presented in Table 9-17. Evenwhen stabilized materials are used, properconstruction techniques and control practicesare mandatory.

THICKNESS DESIGN PROCEDURESThe first paragraphs of this section give

the design engineer information concerningsoil stabilization for construction of theater-of-operations roads and airfields. The

information includes procedures for deter-mining soil’s suitability for stabilization anda means of determining the appropriate typeand amount of stabilizer to be used. The finalobjective in this total systematic approach isto determine the required design thicknesses.Depending on the type of facility and the AI orthe CBR of the unstabilized subgrade, thedesign procedure presented in this section al-lows determination of the required thicknessof an overlying structure that must be con-structed for each anticipated facility.

This basic structural design problem mayhave certain conventional overriding factors,

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such as frost action, that influence this re-quired thickness. The decision to stabilize ornot may be based on factors other than struc-tural factors, such as economy, availability ofstabilizer, and time. It must be realized thatsoil stabilization is not a cure for all militaryengineering problems. Proper use of thismanual as a guide allows, in some cases,reductions in required thicknesses. Theprimary benefit in soil stabilization is that itcan provide a means of accomplishing orfacilitating construction in situations inwhich environmental factors or lack ofsuitable materials could preclude or seriouslyhamper work progress. Through the properuse of stabilization, marginal soils can oftenbe transformed into acceptable constructionmaterials. In many instances, the quantity ofmaterials required can be reduced andeconomic advantages gained if the cost ofchemical stabilization can be offset by asavings in material transportation costs.

The structural benefits of soil stabilization,shown by increased load-carrying capability,are generally known. In addition, increasedstrength and durability also occur withstabilization.

Generally, lesser amounts of stabilizersmay be used for increasing the degree ofworkability of a soil without effectively in-creasing structural characteristics. Also,greater percentages may be used for increas-ing strength at the risk of being uneconomicalor less durable. Some of the informationpresented is intended for use as guidance onlyand should not supersede specific trial-proven methods or laboratory testing wheneither exists.

Primary considerations in determiningthickness design are those that involve thedecision to construct a single-layer or multi-layer facility, as discussed earlier. Themethod chosen depends on the type of con-struction. All permanent construction andmost multi layer designs should use thereduced thickness design procedure. Usuallythe single layer is of expedient design.

ROADSSpecific procedures for determining total

and/or layer thicknesses for roads are dis-

Soil Stabilization for Roads and Airfields 9-30

cussed below. The more expedient methodsare shown first, followed by more elaborateprocedures. Road classification is based onequivalent number 18-kip, single-axle, dual-wheel applications. Table 9-18 lists theclasses of roads.

Single-LayerFor each category of roads (Classes A

through E), a single design curve is presentedthat applies to all types of stabilization (seeFigures 9-12 through 9-14 and Figure 9-16,page 9-32). These curves indicate the totalpavement thickness required on an unstabil-ized subgrade over a range of subgradestrength values. It should be noted that eachcurve terminates above a certain subgradeCBR. This is because design strength criteriafor unsurfaced roads indicate that a naturalsoil of this appropriate strength could sustainthe traffic volume required of this category offacility without chemical stabilization. Thefollowing flow diagram indicates the use ofthese design procedures:

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On a single-layer road, a thin wearingcourse may be advisable to provide water-proofing and to offset the effects of tireabrasion.

MultilayerFor each road category, four design curves

are shown (see Figures 9-16 and 9-17 andFigures 9-18 and 9-19, page 9-34). These cur-ves indicate the total thickness required forpavements incorporating one of the followingcombinations of soil and stabilizer:

Lime and fine-g-rained soils.Asphalt and coarse-grained soils.Portland cement and coarse-graind soils.

Coarse- and fine-g-rained soils are definedaccording to the USCS. The curves presentedin Figures 9-16 and 9-17 and Figures 9-18

and 9-19, page 9-34, are applicable over arange of subgrade CBR values.

Individual layer thickness can be ac-complished using Table 9-19, page 9-35. Thistable indicates minimum base and wearingcourse thickness requirements for road Clas-ses A through E. Minimum surface coursethickness requirements are indicated for abase course with a strength of 50 to 100 CBR.If a stabilized soil layer is used as a subbase,the design base thickness is the total thick-ness minus the combined thickness of baseand wearing courses. If a stabilized layer isused as a base course over an untreated sub-grade, the design base thickness is the totalthickness minus the wearing course thick-ness. The following flow diagram showsthese procedures:

Soil Stabilization for Roads and Airfields 9-32

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Soil Stabilization for Roads and Airfields 9-33

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Soil Stabilization for Roads and Airfields 9-34

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Reduced thickness design factors, (see-Table 9-20 and Figure 9-20, page 9-36 ) shouldbe applied to conventional design thicknesswhen designing for permanent and nonex-pedient road and airfield design. The use ofstabilized soil layers within a flexible pave-ment provides the opportunity to reduce theoverall thickness of pavement structure re-quired to support a given load. To design apavement containing stabilized soil layers re-quires the application of equivalency factorsto a layer or layers of a conventionallydesigned pavement. To qualify for applicationof equivalency factors, the stabilized layermust meet appropriate strength anddurability requirements set forth in TM5-822-4/AFM 88-7, Chapter 4. An equivalen-cy factor represents the number of inches of aconventional base or subbase that can bereplaced by 1 inch of stabilized material.Equivalency factors are determined from—

Table 9-20 for bituminous stabilizedmaterials.Figure 9-20, page 9-36, for materialsstabilized with cement, lime, or acombination of fly ash mixed withcement or lime.

Selection of an equivalency factor from thetabulation depends on the classification ofthe soil to be stabilized. Selection of an

equivalency factor from Figure 9-20, page9-36, requires that the unconfined compres-sive strength, determined according to ASTMD1633, is known. Equivalency factors aredetermined from Figure 9-20, page 9-36, forsubbase materials only. The relationship es-tablished between abase and a subbase is 2:1.Therefore, to determine an equivalency factorfor a stabilized base course, divide the sub-base factor from Figure 9-20, page 9-36, by 2.See TM 5-330/AFM 86-3, Volume II for con-ventional design procedures.

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AIRFIELDSSpecific procedures for determining the

total and/or layer thicknesses for airfields arediscussed in the following paragraphs. Themore expedient methods are shown first, fol-lowed by more elaborate procedures.Airfields are categorized by their position onthe battlefield, the runway length, and thecontrolling aircraft. Table 9-21 lists aircraftcategories.

Single-LayerDesign curves for single-layer airfield con-

struction are in Figures 9-21 through 9-28,pages 9-38 through 9-44. In these figures

the controlling aircraft and design life incycles (one cycle is one takeoff and one land-ing) are indicated for each airfield cate-gory. The design curves are applicable for alltypes of stabilization over a range of subgradestrengths up to a maximum above whichstabilization would generally be unwar-ranted if the indicated material subgradestrength could be maintained. Design curvesare presented for typical theater-of-opera-tions gross weights for the controlling aircraftcategory. For a single-layer facility, a thinwearing course may provide waterproofing orminimize abrasion resulting from aircrafttires. The following flow diagram indicatesthese procedures:

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Soil Stabilization for Roads and Airfields 9-37

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Soil Stabilization for Roads and Airfields 9-38

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Soil Stabilization for Roads and Airfields 9-39

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Soil Stabilization for Roads and Airfields 9-40

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Soil Stabilization for Roads and Airfields 9-41

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MultilayerIn the design of multilayer airfields, it is

first necessary to determine the total designthickness based on conventional flexiblepavement criteria. Then an appropriatereduction factor is applied for the particularsoil-stabilizer combination anticipated foruse. Determinations of individual layerthickness finalizes the design. Conventional

flexible pavement design curves and proce-dures may be found in TM 5-330/AFM 86-3,Volume II. After total thickness has beendetermined, a reduction factor is applied (seeTable 9-22 or 9-23, page 9-45). Individuallayer thicknesses can be determined usingTable 9-24, page 9-46, and procedures indi-cated for multi layer roads. The following flowdiagram indicates these design procedures:

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Soil Stabilization for Roads and Airfields 9-43

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Soil Stabilization for Roads and Airfields 9-44

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EXAMPLES OF DESIGNUse of the design criteria in this section can

best be illustrated by examples of typicaldesign situations.

Example 1The mission is to construct an airfield for

the logistical support of an infantry divisionand certain nondivision artillery units. Thefacility must sustain approximately 210takeoffs and landings of C-130 aircraft,operating at 150,000 pounds gross weight,along with operations of smaller aircraft. Be-cause of unsatisfactory soil strengthrequirements and availability of chemicalstabilizing agents, stabilization is to be con-sidered. The facility is also considered anexpedient single-layer design.

A site reconnaissance and a few soilsamples at the proposed site indicate the fol-lowing:

The natural strength is 8 CBR.It has a PI of 15.It has a LL of 30.Twenty percent passes a Number 200sleve.

Thirty percent is retained on a Num-ber 4 sieve.

The classification is (SC).

Using this information, a determinationcan be made from Figure 9-4, page 9-12, andTable 9-3, page 9-13, that the proper agent iscement, lime, or fly ash. The soil-lime pH testindicates that a lime content of 3 percent is re-quired to produce a pH of 12.4. Since the soilclassified as an (SC), an estimated cementcontent of 7 percent is selected from Table9-7, page 9-15. The fly ash ratio is 4 percentlime, 1 percent cement, 16 percent fly ash,and 79 percent soil. The characteristics of alladditives are then reviewed, and because ofpredicted cool weather conditions, cementstabilization is chosen.

The design thickness is then determined.The facility will be designed as a close battlearea 3,000’ airfield designed for 420 cycles of aC-130 aircraft. To determine the designthickness. Figure 9-1, page 9-7, is used. For asubgrade strength of 8 CBR and interpolatingbetween the 125,000- and 175,000-pound cur-ves, the required design thickness is 13 1/2inches.

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Example 2The mission is to provide a rear area 6)000’

airfield facility for C-5A aircraft operating at320,000 pounds gross weight. Time andmaterials indicate that a multilayer facilitycan be constructed using nonexpedientmethods. A site reconnaissance indicates thefollowing:

The natural strength is 5 CBR.It has a PI of 5.It has a LL of 35.Fifteen percent passes the Number200 sieve.Sixty percent is retained on the Num-ber 4 sieve.The classification is (GM).

Chemical stabilization is considered for theupper subgrade, but a supply of 100-CBRbase course material is available. An asphal-tic concrete wearing course will be used.Since the soil classified as (GM), either

bituminous, fly ash, or cement stabilization isappropriate (see Figure 9-4, page 9-12, andTable 9-3, page 9-13). Because of the lack ofadequate quantities of cement and fly ash,bituminous stabilization will be tried.

The material is termed “sand-gravelbitumen. ” Table 9-13, page 9-24, recom-mends either asphalt cutbacks or emulsions(considerable materials passing the Number200 sieve); since cutback asphalt is available,it will be used. It is anticipated that the in-place temperature of the sand will be about100 degrees Fahrenheit. (From Table 9-13,page 9-24, it can then be determined that thegrade of cutback to be used is MC-800. Fromthe equation given on page 9-23 and thegradation curve (not shown for the example),a preliminary design content of 6.7 percentasphalt is determined.) Design specimensare then molded and tested using the proce-dures indicated in TM 5-530. Comparing thetest results with the criteria given previously

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(a minimum of 500 pounds), it can be deter-mined that the upper subgrade can bestabilized with cutback asphalt. An optimumasphalt content of 6.5 percent is indicated.

The design thickness is then determined.(Only procedures for determining designthickness of a Type A runway area will be in-dicated.) Since the airfield is a rear-area6,000’ facility with the C-141 as the control-ling aircraft category and is a multilayerdesign, TM 5-330, Figure D-36 is used. A sub-grade strength of 5 CBR and a designthickness of 45 inches is required for a con-ventional pavement. Since soil stabilizationis involved, reduced thickness design is al-lowed. Table 9-20, page 9-35, shows that theequalizing factor for an asphalt-stabilizedsubbase of a (GM) soil is 2.00. Therefore, therequired thickness for the pavement, includ-ing the surface and base course, is 22.5inches.

To determine individual layer thicknesses,use Table 9-24. For a rear-area, 6,000’ air-field with the C-141 as the controlling aircraftand a 100 CBR base-course strength, the mini-mum surface-course and base coursethicknesses are 2 1/2 and 6 inches, respective-ly. Thus, the individual layer thicknesswould be as follows: surface course, 2 1/2 in-ches; 100-CBR base course, 6 inches; andstabilized upper subgrade, 14.0 inches.Another viable solution would be to stabilizethe base course also.

Example 3The mission is to quickly provide an ex-

pedient road of geometrical classificationbetween two organizational units. Only thein-place material can be stabilized. Thepreliminary site investigation indicates thefollowing:

The natural strength is 15 CBR.It has a PI of 15.It has a LL of 30.Sixty percent passes a Number 40sieve.Fifty-five percent passes a Number200 sieve.The classification is (CL).

Expedient design procedures indicate thatlime or cement stabilization is feasible (seeTable 9-3, page 9-13, and Figure 9-4 page9-12). Only lime is readily available, Designprocedures for a single-layer C1ass E road willbe used. Figure 9-6, page 9-20, is used todetermine the initial design lime content,Since the soil has a PI of 15 and 60 percentpassing the number 40 sieve, an estimatedlime content of 2 1/2 percent is selected. Fig-ure 9-15, page 9-32, indicates that therequired design thickness of stabilizedmaterial is 9 inches.

Example 4The mission is to construct a road between

two rear-area units. Time and material con-ditions allow nonexpedient procedures. Ahot-mix plant is available so that an asphalticconcrete wearing course can be applied. How-ever, the upper portion of the in-placematerial must be upgraded to provide asuitable base course. Geometric criteria indi-cate that a Class D multi layer road isrequired. A soil survey reveals the followingwith respect to the in-place material:

The average soil strength is 7 CBR.It has a PI of 9.It has a LL of 25.Thirty-seven percent passes the Num-ber 200 sieve.Forty-five percent passes the Number4 sieve (25 percent is smaller than0.05 mm, and 5 percent is smallerthan 0.005 mm).The classification is (GC).

Following procedures in Figure 9-4, page9-12, and Table 9-3, page 9-13, it is deter-mined that cement or lime-cement-fly ashstabilization will work with this soil; how-ever, fly ash is not available. The soil-cementlaboratory test (see TM 5-530) is run. Testresults indicate that a cement content of 6percent is required. Figure 9-18, page 9-34, in-dicates that a total pavement thickness of 12inches is required above the 7-CBR subgradefor a cement-stabilized, coarse-grained soil.A minimum base-course strength of 70 CBR isassumed. Table 9-18, page 9-30, indicatesthat a Class D road is designed for 4.7 x 107

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18-kip equivalent loads and a CBR of 50; a 4-inch asphaltic cement pavement and a10-inch cement-stabilized base are required.

Example 5The mission is to provide an expedient tac-

tical support area airfield for the operation ofapproximately 7,000 cycles of F-4C traffic.The single-layer design is selected. A sitereconnaissance reveals the following:

The natural strength is 4 CBR.It has a PI of 12.Eleven percent passes a Number 200sieve.Twenty percent retained on a Num-ber 4 sieve.Organic material occurs as a trace inthe soil samples.

Climatological data indicate a trend forsubfreezing weather, and full traffic must beapplied immediately upon completion. Or-dinarily, based on information from Figure9-4, page 9-12, and Table 9-3, page 9-13,either cement, lime, or fly ash stabilizationwould be the appropriate agent for this situa-tion and the soil would classify as an (SW-SM)borderline. With the constraints on curingtimes, soil stabilization would not be the ap-propriate method of construction. Anothermeans, possibly landing mats, must be con-sidered for the successful completion of themission.

Example 6The mission is to provide an expedient

Class E road between two organizational taskforces. The single-layer design is selected.The preliminary site investigation for a por-tion of the road indicates a natural soilstrength of 30 CBR. The design curve for thisroad classification, shows that a 30-CBR soilis adequate for the intended traffic and that itdoes not require any stabilization (see Figure9-15, page 9-32). Therefore, no soil samplingor testing is necessary. A problem area maylater arise from a reduction of strength, thatis, a large volume of rainfall or a dust problemon this particular road.

THEATER-OF-OPERATIONS AIRFIELDCONSIDERATIONS

In the theater of operations, the lack oftrained personnel, specialized equipment, ortime often eliminates consideration of manylaboratory procedures. The CBR and specialstabilization tests in particular will not beconsidered for these reasons. As a result,other methods for determining design pave-ment thicknesses have been developed usingthe AI (see TM 5-330/AFM 86-3, Volume II).This system is purely expedient and shouldnot replace laboratory testing and reducedthickness design procedures.

Functions of Soil StabilizationAs previously discussed, the three primary

functions of stabilization are—Strength improvement.Dust control.Waterproofing.

Use of Table 9-25 allows the engineer toevaluate the soil stabilization functions asthey relate to different types of theater-of-operations airfields. It is possible to easilysee the uses of stabilization for the traffic ornontraffic areas of airfields. This table,developed from Table 9-26, page 9-50, showsthe possible functional considerations forsituations where either no landing mat, alight-duty mat, or a medium-duty mat may beemployed. (Landing mats are discussed inTM 5-330/AFM 86-3, Volume II and TM5-33 7.) As an example of the use of this table,consider the construction of the “heavy lift inthe support area.”

Referring to the traffic areas, a certain min-imum strength is required for unsurfaced-soiloperations (that is, without a landing mat) orif either the light duty mat (LM) or themedium duty mat (MM) is used. If the exist-ing soil strength is not adequate, stabilizationfor strength improvement may be consideredeither to sustain unsurfaced operations or tobe a necessary base for the landing mat. Fur-ther, if no mat is used, stabilization might beneeded only to provide dust control and/or soil

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waterproofing. If a landing mat is used, how-ever, the functions of dust control and soilwaterproofing would be satisfied andstabilization need not be considered in anyevent. Possible stabilization functions fornontraffic areas have been shown in a similarmanner. For certain airfields, such as the“light lift in the battle area, ” no function forstrength improvement in either traffic or non-traffic areas is indicated. Such airfields havean AI requirement of 5 or more unsurfacedoperations (see Table 9-26, page 9-50). Siteselection should be exercised in most in-stances to avoid areas of less than a 5 AI. Forcertain airfields, such as the “tactical in thesupport area,“ a landing mater improved sur-facing always will be provided. Therefore a“no mat” situation pertains only to the non-traffic areas.

Design Requirementsfor Strength Improvement

Where stabilization for strength improve-ment is considered, certain basic designrequirements, in terms of strength and thick-ness of a stabilized soil layer on a givensubgrade, must be met. The strength andthickness requirements vary depending onthe operational traffic parameters andthe strength of the soil directly beneath thestabilized soil layer. Since the trafficparameters are known for each airfield type,a minimum strength requirement for the sta-bilized soil layer can be specified for eachairfield based on unsurfaced-soil criteria. Forany given subgrade condition, the thicknessof a minimum-strength, stabilized-soil layernecessary to prevent overstress of the sub-grade also can be determined. Table 9-27,page 9-52, gives design requirements for traf-fic and nontraffic areas of different airfieldtypes for which stabilization may be used forstrength improvement. As seen, the mini-mum-strength requirement in terms of AI is afunction only of the applied traffic for a par-ticular airfield and is independent of thesubgrade strength. However, the thickness isa direct function of the underlying subgradestrength.

Proper evaluation of the subg-rade is essen-tial for establishing thickness requirements.

In evaluating the subgrade for stabilizationpurposes, a representative AI strength profilemust be established to a depth that wouldpreclude the possibility of overstress in theunderlying subgrade. This depth variesdepending on the—

Airfield.Pattern of the profile itself.Manner of stabilization.

In this regard, the thickness data given inTable 9-27, page 9-52, can be used also to pro-vide guidance in establishing an adequatestrength profile. Generally, a profile to adepth of 24 inches is sufficient to indicate thestrength profile pattern. However, if adecrease in strength is suspected in greaterdepths, the strength profile should be ob-tained to no less than the thickness indicatedin Table 9-27, page 9-52, under the 5-6 sub-grade AI column for the appropriate airfield.

The use of Table 9-27, page 9-52, to estab-lish the design requirements for soilstabilization is best illustrated by the follow-ing example: Assume that a rear area 3,500’airfield is to be constructed and that a sub-grade AI evaluation has been made fromwhich a representative profile to a sufficientdepth can be established. One of threegeneral design cases can be considered de-pending on the shape of the strength profile.

The first case considers constantstrength with depth; therefore, the re-quired thickness is read directly fromTable 9-27, page 9-52, under the ap-propriate subgrade AI column. Thus,in the example, if a subgrade AI of 8is measured, the required thickness ofa stabilized soil layer if no landingmat were used would be 18 inches.The required minimum strength ofthis stabilized soil layer is an AI of15. If the light landing mat wereused, a 6-inch-thick layer with a min-imum AI of 10 would be required as abase overlying the subgrade AI of 8.The second case considers an increasein strength with depth; therefore, therequired thickness of stabilization

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may be considerably less than indi-cated in the table. For this example,assume that the AI increases withdepth as shown in Figure 9-29. A sta-bilized layer can be provided either bybuilding up a compacted base cm topof the existing ground surface or bytreating the in-place soil. Because ofthis, each situation represents asomewhat different design problem.

An in-place treatment is analogous toreplacing the existing soil to some depth withan improved quality material. Wherestrength increases with depth, the point atwhich thickness is compatible with thestrength at that particular point must bedetermined. This point can be determinedgraphically simply by superimposing a plot ofthe thickness design requirements versussubgrade AI (see Table 9-27) directly on thestrength profile plot. This procedure isshown in Figure 9-29. The depth at which thetwo plots intersect is the design thickness re-quirement for a stabilized-soil layer. In theexample, a thickness of 9.5 inches (or say 10inches) is required.

If a compacted base of a select borrow soil isused to provide a stronger layer on the sub-grade shown in Figure 9-29, the thicknessmust again be consistent with the strength atsome depth below the surface of the placedbase-course layer. Since the base-courselayer itself will be constructed to a minimumAI of 15, the weakest point under the placedbase will be at the surface of the existingground, or in this instance an AI of 8. Usingthis value, Table 9-27 gives a thickness of 18inches of base course. Compaction of the ex-isting ground would be beneficial in terms ofthickness requirements if it would increasethe critical subgrade strength to a highervalue. If, for example, the minimum AI of theexisting ground could be increased from 8 to12, the thickness of base required would bereduced to 10 inches (see Table 9-27).

The third case considers a decrease instrength with depth. The strengthprofile shown in Figure 9-30, page9-54 indicates a crust of firm material

over a significantly weaker zone ofsoil beneath. In this example, the impor-tance of proper analysis of subgradeconditions is stressed. If strength datawere obtained to less than 30 inches,the adequacy of the design could notbe fully determined.

Consider again an in-place stabilizationprocess. Although the strength profile anddesign curve intersect initially at a shallowdepth (about 3 inches) (see Figure 9-30, page9-54), the strength profile does not remain tothe right of the design curve. This indicatesthat the design requirement has been satis-fied. The second and final intersection occursat 24 inches. Since there is no indication of afurther decrease in strength with depth, athickness of 24 inches is therefore required.

In the case of a compacted base placed on asubgrade that decreases in strength withdepth, the procedure for determining thedesign thickness is more difficult. The designthickness can be determined by comparingthe strength-depth profile with the designcurve. If the measured AI at any given depthis less than the minimum requirement shownby the design curve, a sufficient thickness ofimproved quality soil must be placed on theexisting ground surface to prevent overstress

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at that depth. However, the thickness of basenecessary must be such that the require-ments will be met at all depths. To satisfythis condition, the required thickness must beequal to the maximum difference, which willoccur at a particular strength value, betweenthe depth indicated by the design curve andthe depth from the strength-depth profile, Inthe example shown in Figure 9-30, this max-imum difference occurs at an AI of 12. Thedifference is 10 inches, which is the requiredthickness for an improved quality base.

The same procedures described for adecrease in strength with depth can be usedto derive the strength and thickness require-ments for a base course under either an LM orMM. The thickness design requirementsgiven herein are for stabilized soil layershaving a minimum strength property to meetthe particular airfield traffic need. Although

the strength actually achieved may well ex-ceed the minimum requirement, noconsideration should be given to reducing thedesign thickness as given in Table 9-27, page9-52, or as developed by the stated proce-dures.

Section III. Dust Control

EFFECTS OF DUSTDust can be a major problem during combat

(and training) operations. Dust negativelyimpacts morale, maintenance, and safety.Experience during Operation DesertShield/Storm suggests that dust was a majorcontributor to vehicle accidents. It also ac-celerated wear and tear on vehicles andaircraft components.

Dust is simply airborne soil particles. As ageneral rule, dust consists predominantly ofsoil that has a particle size finer than 0.074mm (that is, passing a Number 200 sieve).

The presence of dust can have significantadverse effects on the overall efficiency ofaircraft by—

Increasing downtime and mainte-nance requirements.Shortening engine life.Reducing visibility.Affecting the health and morale ofpersonnel.

In addition, dust clouds can aid the enemy byrevealing positions and the scope of opera-tions.

DUST FORMATIONThe presence of a relative amount of dust-

size particles in a soil surface does notnecessarily indicate a dust problem nor theseverity of dust that will result in varioussituations. Several factors contribute to thegeneration, severity, and perpetuity of dustfrom a potential ground source. These in-clude—

Overall gradation.Moisture content.Density and smoothness of theground surface.

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Presence of salts or organic matter,vegetation, and wind velocity anddirection.Air humidity.

When conditions of soil and environmentare favorable, the position of an external forceto a ground surface generates dust that existsin the form of clouds of various density, size,and height above the ground. In the case ofaircraft, dust may be generated as a result oferosion by propeller wash, engine exhaustblast, jet-blast impingement, and the draft ofmoving aircraft. Further, the kneading andabrading action of tires can loosen particlesfrom the ground surface that may become air-borne.

On unsurfaced roads, the source of dustmay be the roadway surface. Vehicle trafficbreaks down soil structure or abrades gravelbase courses, creating fine-grained particlesthat readily become airborne when trafficked.

DUST PALLIATIVESThe primary objective of a dust palliative is

to prevent soil particles from becoming air-borne. Dust palliative may be required forcontrol of dust on nontraffic or traffic areas orboth. If a prefabricated landing mat,membrane, or conventional pavement surfac-ing is used in the traffic areas of an airfield,the use of dust palliative would be limited tonontraffic areas. For nontraffic areas, a pal-liative is needed that can resist the maximumintensity of air blast impingement by anaircraft or the prevailing winds. Where dustpalliative provide the necessary resistanceagainst air impingement, they may be totallyunsuitable as wearing surfaces. An impor-tant factor limiting the applicability of a dustpalliative in traffic areas is the extent of sur-face rutting that will occur under traffic. lfthe bearing capacity allows the soil surface torut under traffic, the effectiveness of a shal-low-depth palliative treatment could bedestroyed rapidly by breakup and subsequentstripping from the ground surface. Some pal-liatives tolerate deformations better thanothers, but normally ruts 1½ inches deepresult in the virtual destruction of any thinlayer or shallow depth penetration dust pal-liative treatment.

The success of a dust-control programdepends on the engineer’s ability to match adust palliative to a specific set of factors af-fecting dust generation. These factorsinclude—

Intensity of area use.Topography.Soil type.Soil surface features.Climate.

Intensity of Area UseAreas requiring dust-control treatments

should be divided into traffic areas based onthe expected amount of traffic. The threeclasses of traffic areas are—

Nontraffic.Occasional traffic.Traffic.

Nontraffic Areas. These areas requiretreatment to withstand air-blast effects fromwind or aircraft operations and are not sub-jected to traffic of any kind. Typicalnontraffic areas include—

Graded construction areas.Denuded areas around the peripheryof completed construction projects.Areas bordering airfield or heliportcomplexes.Protective petroleum, oil, and lubri-cant (POL) dikes.Magazine embankments or ammuni-tion storage barricades.Bunkers and revetments.Cantonment, warehouse, storage, andhousing areas, excluding walkwaysand roadways.Unimproved grounds.Areas experiencing wind-borne sand.

Occasional-Traffic Areas. Besides resist-ing helicopter rotor downwash, aircraftpropwash, and air blast from jet engines,these areas are also subjected to occasionaltraffic by vehicles, aircraft, or personnel.Vehicle traffic is limited to occasional, non-channelized traffic. Typical occasional-traffic areas include the following:

Shoulders and overruns of airfields.

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Shoulders, hover lanes, and peri-pheral areas of heliports and heli-pads.Nontraffic areas where occasionaltraffic becomes necessary.

Traffic Areas. Areas subjected to regularchannelized traffic by vehicles, aircraft, orpersonnel. Properly treated traffic areasresist the effects of air blasts from fixed- orrotary-wing aircraft. Typical traffic areas in-clude:

Roadways and vehicle parking areas.Walkways.Open storage areas.Construction sites.Runways, taxiways, shoulders, over-runs, and parking areas of airfields.Hover lanes and landing and parkingpads of heliports.Tank trails.

TopographyDust palliative for controlling dust on flat

and hillside areas are based on the expectedtraffic, but the specific palliative selected maybe affected by the slope. For example, a liquidpalliative may tend to run off rather thanpenetrate hillside soils, which degrades thepalliative’s performance.

Divide the area to be treated into flat andhillside areas. Flat is defined as an averageground slope of 5 percent or less, whilehillside refers to an average ground slopegreater than 5 percent. Particular areas canbe given special attention, if required.

Soil TypeSoil type is one of the key features used to

determine which method and material shouldbe used for dust control. Soils to be treated fordust control are placed into five generaldescriptive groupings based on the USCS.They are—

Silts or clays (high LL) (types (CH),(OH), and (MH)).Silts or clays (low LL) (types (ML),(CL), (ML-CL), and (OL)).

Sands or gravels (with fines) (types(SM), (SC), (SM-SC), (GM), (GC),(GM-GO, and (GW-GM)).Sands (with little or no fines) (types(SW-SM), (SP), and (SW)).Gravels (with little or no fines) (types(GP) and (GW)).

Soil Surface FeaturesSoil surface features refer to both the state

of compaction and the degree of soil satura-tion in the area to be treated. Loose surfaceconditions are suitable for treatment in non-traffic or occasional areas only. Firm surfaceconditions are suitable for treatment underany traffic condition.

Loose and Dry or Slightly Damp Soil. Thesurface consists of a blanket (¼ to 2 inchesthick) of unbound or uncompactedsoil, overlying a relatively firm subgrade andranging in moisture content from dry toslightly damp.

Loose and Wet or Scurry Soil. The surfacecondition consists of a blanket ( ¼ to 2 inchesthick) of unbound or uncompacted soil, over-lying a soft to firm subgrade and ranging inmoisture content from wet to slurry consis-tency. Soil in this state cannot be treateduntil it is dried to either a dry or slightly dampstate.

Firm and Dry or Slightly Damp Soil. Thesurface condition consists of less than a ¼-inch-thick layer of loose soil, ranging inmoisture content from dry to slightly dampand overlying a bound or compacted firm soilsubgrade.

Firm and Wet Soil. The surface conditionresembles that of the previous category. Thissoil must be dried to either a dry or slightlydamp state before it can be treated.

ClimateClimatic conditions influence the storage

life, placement, curing, and aging of dust pal-liative. The service life of a dust palliativemay vary with the season of the year. For ex-ample, salt solutions become ineffective

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during the dry season when the relativehumidity drops below 30 percent.

DUST-CONTROL METHODSThe four general dust-control-treatment

methods commonly used are—Agronomic.Surface penetrant.Admix.Surface blanket.

AgronomicThis method consists of establishing,

promoting, or preserving vegetative cover toprevent or reduce dust generation from ex-posed soil surfaces. Vegetative cover is oftenconsidered the most satisfactory form of dustpalliative. It is aesthetically pleasing,durable, economical, and considered to bepermanent. Some agronomic approachesto dust control are suitable for theater-of-operations requirements. Planning construc-tion to minimize disturbance to the existingvegetative cover will produce good dust-palliative results later.

Agronomic practices include the use of—Grasses.Shelter belts.Rough tillage.

Grounds maintenance management and fer-tilizing will help promote the development ofa solid ground cover. Agronomic methods arebest suited for nontraffic and occasional-traffic areas; they are not normally used intraffic areas.

Grasses. Seeding, sprigging, or soddinggrasses should be considered near theater-of-operations facilities that have a projecteduseful life exceeding 6 months. Combiningmulch with seed promotes quicker estab-lishment of the grass by retaining moisture inthe soil. Mulching materials include straw,hay, paper, or brush. When mulches arespread over the g-round, they protect the soilfrom wind and water erosion. Mulches are ef-fective in preventing dust generation onlywhen they are properly anchored. Anchoring

can be accomplished by disking or by applyingrapid curing (RC) bituminous cutbacks orrapid setting (RS) asphalt emulsions. Mulchis undesirable around airports and heliportssince it may be ingested into jet engines,resulting in catastrophic engine failure.

Shelter Belts. They are barriers formed byhedges, shrubs, or trees that are high anddense enough to significantly reduce windvelocities on the leeward side. Their place-ment should be at right angles to theprevailing winds. While a detailed discussionof shelter-belt planning is beyond the scope ofthis manual, shelter belts should be con-sidered for use on military installations andnear forward landing strips (FLS) con-structed for contingency purposes in austereenvironments (such as those constructed inCentral America).

Rough Tillage. This method consists ofusing a chisel, a lister, or turning plows to tillstrips across nontraffic areas. Rough tillageworks best with cohesive soils that form clods.It is not effective in cohesionless soils and, ifused, may contribute to increased dustgeneration.

Surface PenetrantThe surface penetration method involves

applying a liquid dust palliative directly tothe soil surface by spraying or sprinkling andallowing the palliative to penetrate the sur-face. The effectiveness of this methoddepends on the depth of penetration of thedust palliative (a function of palliative vis-cosity and soil permeability). Using water toprewet the soil that is to be treated enhancespenetration of the palliative.

Surface penetrants are useful under alltraffic conditions; however, they are only ef-fective on prepared areas (for example, onunsurfaced gravel roads). Dust palliativethat penetrate the soil surface include—

Bitumens.Resins.Salts.Water.

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Bitumens. Conventional types of bitu-minous materials that may be used for dustpalliative include—

Cutback asphalts.Emulsified asphalts.Road tars.Asphaltic penetrative soil binder(APSB).

These materials can be used to treat bothtraffic and nontraffic areas. All bituminousmaterials do not cure at the same rate. Thisfact may be of importance when they arebeing considered for use in traffic areas. Also,bituminous materials are sensitive toweather extremes. Usually bituminousmaterials impart some waterproofing to thetreated area that remains effective as long asthe treatment remains intact (for example, asplaced or as applied). Bituminous materialsshould not be placed in the rain or when rainis threatening.

A cutback asphalt (cutbacks) is a blend ofan asphalt cement and a petroleum solvent.These cutbacks are classified as RC, mediumcuring (MC), and slow curing (SC), dependingon the type of solvent used and its rate ofevaporation. Each cutback is further gradedby its viscosity. The RC and SC grades of 70and 250, respectively, and MC grades of 30,70, and 250 are generally used. Regardless ofclassification or grade, the best results are ob-tained by preheating the cutback. Sprayingtemperatures usually range from 120 to 300degrees Fahrenheit. The actual range for aparticular cutback is much narrower andshould be requested from the supplier at thetime of purchase. The user is cautioned thatsome cutbacks must be heated above theirflash point for spraying purposes; therefore,no smoking or open flames should be per-mitted during the application or the curing ofthe cutback. The MC-30 grade can besprayed without being heated if the tempera-ture of the asphalt is 80 degrees Fahrenheitor above. A slightly moist soil surface assistspenetration. The curing time for cutbacksvaries with the type. Under favorable groundtemperature and weather conditions, RCcures in 1 hour, MC in 3 to 6 hours, and SC in

1 to 3 days. In selecting the material for use,local environmental protection regulationsmust be considered.

Asphalt emulsions (emulsions) are a blendof asphalt, water, and an emulsifying agent.They are available either as anionic orcationic emulsions. The application of emul-sions at ambient temperatures of 80 degreesFahrenheit or above gives the best results.Satisfactory results may be obtained belowthis temperature, especially if the applicationis made in the morning to permit the warmingeffects of the afternoon sun to aid in curing.Emulsions should not be placed at tempera-tures below 50 degrees Fahrenheit.Emulsions placed at temperatures belowfreezing will freeze, producing a substandardproduct. For best results in a freezing en-vironment, emulsions should be heated tobetween 75 and 130 degrees Fahrenheit. Thetemperature of the material should never ex-ceed the upper heating limit of 185 degreesFahrenheit because the asphalt and waterwill separate (break), resulting in materialdamage. Emulsions generally cure in about 8hours. The slow setting (SS) anionic emul-sions of grades SS-1 and SS-lh may be dilutedwith 1 to 5 or more parts water to one partemulsified asphalt by volume before using.As a general rule, an application of 3 partswater to 1 part emulsion solution is satisfac-tory. The slow-setting cationic emulsions orgrades cationic slow setting (CSS)-1 and CSS-1h are easiest to use without dilution. Ifdilution is desired, the water used must befree of any impurities, minerals, or salts thatmight cause separation (breaking) of theemulsion within the distribution equipment.

Road tars (RTs) (tars) are viscous liquidsobtained by distillation of crude tars obtainedfrom coal. Tars derived from other basicmaterials are also available but are not nor-mally used as soil treatments. Tars aregraded by viscosity and are available ingrades ranging from 1 to 12. They are alsoavailable in the road tar cutback (RTCB) formof viscosity grades 5 and 6 and in the emul-sified form. Tar emulsions are difficult toprepare and handle, The low-viscositygrades RT-1 and RT-2 and the RTCB gradescan be applied at temperatures as low as 60

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degrees Fahrenheit without heating. The tarcutbacks generally have better penetratingcharacteristics than asphalts and normallycure in a few hours. Tars produce excellentsurfaces, but curing proceeds very slowly.Several days or even weeks may be requiredto obtain a completely cured layer. Tars aresusceptible to temperature changes and maysoften in hot weather or become brittle in coldweather.

APSB, a commercial product, is a specialliquid asphalt composed of a high penetrationgrade of asphalt and a solvent blend ofkerosene and naphtha. It is similar in char-acter to a standard low-viscosity, medium-curing liquid asphalt} but it differs in manyspecific properties. The APSB is suitable forapplication to soils that are relatively imper-vious to conventional liquid asphalts andemulsion systems. Silts and moderately plas-tic clays (to a PI of 15) can be treatedeffectively. Curing time for the APSB is 6 to12 hours under favorable ground tempera-ture and weather conditions. Onhigh-plasticity solids (with a PI greater than15), the material remains on the surface as anasphalt film that is tacky at a groundtemperature of approximately 100 degreesFahrenheit and above. The APSB must beheated to a temperature between 130 to 150degrees Fahrenheit to permit spraying withan asphalt distributor.

Resins. These dust palliative may be usedas either surface penetrants or surfaceblankets. They have a tendency to eitherpenetrate the surface or form a thin surfacefilm depending on the type of resin used, thesoil type, and the soil condition. Thematerials are normally applicable to nontraf-fic areas and occasional-traffic areas whererutting will not occur. They are not recom-mended for use with silts and clays.

Resin-petroleum-water emulsions arequite stable and highly resistant to weather-ing. A feature of this type of dust palliative isthat the soil remains readily permeable towater after it is treated. This type of productis principally manufactured under the tradename Coherex. Application rates range from

0.33 to 0.5 gallon per square yard. Thematerial may be diluted for spraying using 4parts water to 1 part concentrate. Thismaterial is primarily suited for dry sandysoils; it provides unsuitable results whenused on silty and clayey soils.

Lignin is a by-product of the manufactureof wood pulp. It is soluble in water and there-fore readily penetrates the soil. Its volubilityalso makes it susceptible to leaching from thesoil; thus, application is repeated as neces-sary after rainfall. Lignin is readily availablein the continental United States and certainother sections of the world. It is useful inareas where dust control is desirable for shortperiods of time; it is not recommended for usewhere durability is an important factor. Therecommended application rate is 1 gallon persquare yard of a resinous solution of 8 percentsolid lignin sulphite.

Concrete curing compounds can be used topenetrate sands that contain little or no siltsor clays. This material should be limited toareas with no traffic. The high cost of thismaterial is partly offset by the low applicationrate required (0.1 to 0.2 gallon per squareyard). Standard asphalt pressure dis-tributors can be used to apply the resin;however, the conventional spray nozzlesshould be replaced with nozzles with smalleropenings to achieve a uniform distribution atthe low application rate.

Salts. Salts in water emulsions have beenused with varying success as dust palliative.Dry calcium chloride (CaC12) is deliquescentand is effective when the relative humidity isabout 30 percent or greater. A soil treatedwith calcium chloride retains more moisturethan the untreated soil under comparabledrying conditions. Its use is limited tooccasional-traffic areas, Sodium chloride(NaC1) achieves some dust control by retain-ing moisture and also by some cementingfrom salt crystallization. Both calciumchloride and sodium chloride are soluble inwater and are readily leached from the soilsurface; thus, frequent maintenance is re-quired. Continued applications of salt

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solutions can ultimately build up a thin,crusted surface that will be fairly hard andfree of dust. Most salts are corrosive to metaland should not be stored in the vehicle usedfor application. Magnesium chloride(MgC12) controls dust on gravel roads withtracked-vehicle traffic. Best results can beexpected in areas with occasional rainfall orwhere the humidity is above 30 percent. Thedust palliative selected and the quantity usedshould not exceed local environmental protec-tion regulations.

Water. As a commonly used (but very tem-porary) measure for allaying dust, a soilsurface can be sprinkled with water. As longas the ground surface remains moist or damp,soil particles resist becoming airborne.Depending on the soil and climate, frequenttreatment may be required. Water shouldnot be applied to clay soil surfaces in suchquantity that puddles forms since a muddy orslippery surface may result where the soilremains wet.

AdmixThe admix method involves blending the

dust palliative with the soil to produce auniform mixture. This method requires moretime and equipment than either the penetra-tion or surface blanket methods, but it has thebenefit of increasing soil strength.

Normally, a minimum treatment depth of 4inches is effective for traffic areas and 3 in-ches for other areas. The admixture can bemixed in place or off site. Typical admixturedust palliative include—

Portland cement.Hydrated lime.Bituminous materials.

In-Place Admixing. In-place admixing isthe blending of the soil and a dust palliativeon the site. The surface soil is loosened (ifnecessary) to a depth slightly greater thanthe desired thickness of the treated layer.The dust palliative is added and blended withthe loosened surface soil, and the mixture iscompacted. Powders may be spread by handor with a mechanical spreader; liquids should

be applied with an asphalt distributor.Mixing equipment that can be used in-cludes—

Rotary tillers.Rotary pulverizer-mixers.Graders.Scarifies.Disk harrows.Plows.

Admixing and/or blending should continueuntil a uniform color of soil and dust palliativemixture, both horizontally and vertically, isachieved. The most effective compactionequipment that can be used is a sheepsfoot orrubber-tired rollers. The procedure for in-place admixing closely resembles the soilstabilization procedure for changing soilcharacteristics and soil strength used in roadconstruction. For dust control on a nontrafficarea, adequate compaction can be achieved bytrafficking the entire surface with a 5-tondual-wheel truck. For all other traffic situa-tions, the procedure should follow TM5-822-4. This procedure is time-consumingand requires the use of more equipment thanthe other three. Following placement, admix-ing, and compaction, a minimum of sevendays is required for curing.

Two cementing-type powders (portland ce-ment and hydrated lime) are primarily usedto improve the strength of soils. However,when they are admixed with soils in rela-tively small quantities (2 to 5 percent by drysoil weight), the modified soil is resistant todusting. Portland cement is generally suitedto all soil types, if uniform mixing can beachieved, whereas hydrated lime is ap-plicable only to soils containing a highpercentage of clay. The compacted soil sur-face should be kept moist for a minimum of 7days before allowing traffic on it.

Bituminous materials are more versatilethan cementing materials in providing ade-quate dust control and waterproofing of thesoil. Cutbacks, emulsion asphalts, and roadtars can all be used successfully. The quan-tity of residual bituminous material usedshould range from 2 to 3 percent of dry soil

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weight (for soils having less than 30 percentpassing the Number 200 sieve) to 6 to 8 per-cent (for soils having more than 30 percentfine-grained soils passing the Number 200sieve). The presence of mica in a soil isdetrimental to the effectiveness of a soil-bituminous material admixture. There areno simple guides or shortcuts for designingmixtures of soil and bituminous materials.The maximum effectiveness of soil-bituminous material admixtures can usuallybe achieved if the soil characteristics arewithin the following limits:

The PI is The amount of material passing theNumber 200 sieve is 30 percent byweight.

This data and additional construction datacan be found in TM 5-822-4. Traffic should bedetoured around the treated area until thesoil-bituminous material admixture cures.

Cutback asphalt provides a dust-free,waterproof surface when admixed into soil todepths of 3 inches or more on a firm subgrade.More satisfactory results are obtained if thecutback asphalt is preheated before using it.Soils should be fairly dry when cutback as-phalts are admixed. When using SC or MCtypes of cutback asphalt, aerate the soil-asphalt mixture to allow the volatiles toevaporate.

Emulsified asphalts are admixed with aconditioned soil that allows the emulsion tobreak before compaction. A properly condi-tioned soil should have a soil moisturecontent not to exceed 5 percent in soils havingless than 30 percent passing the Number 200sieve. Emulsified asphalts, particularly thecationics (CSS-1 or CSS-lb), are very sensi-tive to the surface charge of the aggregate orsoil. When they are used improperly, theemulsion may break prematurely or aftersome delay. The slow-setting anionic emul-sions of grades SS-1 and SS-lh are lesssensitive.

Road tars with RT and RTCB grades can beused as admixtures in the same manner as

10.

other bituminous materials. Road tar admix-tures are susceptible to temperature changesand may soften in hot weather or become brit-tle in cold weather.

Off-Site Admixing. Off-site admixing isgenerally used where in-place admixing is notdesirable and/or soil from another sourceprovides a more satisfactory treated surface.Off-site admixing may be accomplished witha stationary mixing plant or by windrow-mixing with graders in a central workingarea. Processing the soil and dust palliativethrough a central plant produces a moreuniform mixture than in-place admixing.The major disadvantage of off-site operationsis having to transport and spread the mixedmaterial.

Surface BlanketThe principle of the surface blanket method

is to place a “blanket” cover over the soil sur-face to control dust. The three types ofmaterials used to form the blanket are—

Minerals (aggregates).Synthetics (prefabricated membranesand meshes).Liquids (bituminous or polyvinyl ace-tate liquids).

These materials may be used alone or in thecombinations discussed later.

The type of treatment used dictates theequipment required. However, in all cases,standard construction equipment can be usedeffectively to place any of the blanketmaterials. Mechanized equipment should beused wherever possible to assure uniformityof treatment.

The surface blanket method is applicable tonontraffic, occasional-traffic, and trafficareas. Aggregate, prefabricated membrane,and mesh treatments are easy to place andcan withstand considerable rutting. Theother surface blanket methods onlywithstand considerable rutting. Once a sur-face blanket treatment is torn or otherwisecompromised and the soil exposed, sub-sequent traffic or air blasts increase the

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damage to the torn surface blanket andproduce dust from the exposed soil. Repairs(maintenance) should begin as soon as pos-sible to protect the material in place and keepthe dust controlled.

Minerals (aggregates). Aggregate is ap-propriate in arid areas where vegetativecover cannot be effectively established. It iseffective as a dust palliative on nontraffic andoccasional-traffic areas. The maximumrecommended aggregate size is 2 inches; ex-cept for airfields and heliports. To preventthe aggregate from being picked up by theprop (propeller) wash, rotor wash, or air blast,4-inch aggregate is recommended (see Table9-28).

Prefabricated Membrane. Membraneused to surface an area controls dust and evenacts as a surface course or riding surface fortraffic that does not rut the soil. When sub-jected to traffic, the membrane can beexpected to last approximately 5 years.Minor repairs can be made easily. For op-timum anchorage, the membrane should beextended into 2-foot-deep ditches at each edgeof the covered area; then it should be staked inplace and the ditches backfilled. Furtherdetails on the use and installation of prefabri-cated membranes can be obtained from TM5-330/AFM 86-3, Volume II.

Prefabricated Mesh. Heavy, woven jutemesh, such as commonly used in conjunctionwith grass seed operations, can be used fordust control of nontraffic areas. The meshshould be secured to the soil by burying the

edges in trenches and by using large U-shaped staples that are driven flush with thesoil surface. A minimum overlap of 3 inchesshould be used in joining rolls of mesh;covered soil should be sprayed with abituminous material. Trial applications arerecommended at each site and should be ad-justed to suit each job situation.

Bituminous Liquid. Single- or double-bituminous surface treatments can be used tocontrol dust on most soils. A medium-curingliquid asphalt is ordinarily used to prime thesoil before placing the surface treatment.Fine-grained soils are generally primed withMC-30 and coarse-grained soils with MC-70.After the prime coat cures, a bituminousmaterial is uniformly applied, and gravel,slag, or stone aggregate is spread over thetreated area at approximately 25 pounds persquare yard. The types of bituminousmaterials, aggregate gradations, applicationrates, and methods of placing surface treat-ments are described in TM 5-822-8/AFM88-6, Chapter 9. Single-or double-bituminoussurface treatments should not be used whereturf is to be established.

Polyvinyl Acetate (DCA 1295) (withoutreinforcement). DCA 1295 has a slight odorand an appearance similar to latex paint.The material is diluted 3 parts DCA 1295 to 1.part water and cures in 2 to 4 hours underideal conditions of moderate to high tempera-ture and low relative humidity. A clear,flexible film forms on the treated surface.DCA 1295 can be sprayed with a conventionalasphaIt distributor provided modificationsare made to the pump to permit external

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lubrications. The DCA 1295 can be usedalone or over a fiberglass reinforcement. Ad-ding fiberglass does not affect the basicapplication procedures or the curing charac-teristics of the DCA 1295. This material issuitable for use on nontraffic, occasional-traffic, and traffic areas. It is also effectivewhen sprayed over grass seed to protect thesoil until grass occurs. Uniform soil coverageis enhanced by sprinkling (presetting) thesurface with water.

Polyvinyl Acetate (DCA 1295) (with rein-forcement). A fiberglass scrim material isrecommended for use with the DCA 1295when a reinforcement is desired. Fiberglassscrirn increases the expected life of the dust-control film by reducing the expansion andcontraction effects of weather extremes. Thescrim material should be composed offiberglass threads with a plain weave patternof 10 by 10 (ten threads per inch in the warpdirection and 10 threads per inch in the filldirection) and a greige finish. It should weighapproximately 1.6 ounces per square yard.Using scrim material does not create anyhealth or safety hazards, and special storagefacilities are not required. Scrim materialscan be applied under any climatic conditionssuitable for dispensing the DCA 1295.(Under special conditions, continuousstrands of fiberglass maybe chopped into l/2-inch-long segments and blown over the areato be protected.) The best method of place-ment is for the fiberglass scrim material to beplaced immediately after presetting withwater, followed by the DCA 1295.

Polypropylene-Asphalt Membrane. Thepolypropylene-asphalt membrane is recom-mended for use in all traffic areas. It hasconsiderable durability and withstands rut-ting up to approximately 2 inches in depth.This system is a combination of apolypropylene fabric sprayed with an asphaltemulsion. Normally a cationic emulsion isused; however, anionic emulsions have alsobeen used successfully. Several types ofpolypropylene fabric are commercially avail-able.

This treatment consists of the followingsteps:

Place a layer of asphalt (0.33 to 0.50gallon per square yard) on theground, and cover this with a layerof polypropylene fabric.Place 0,33 gallon per square yard ofasphalt on top of the polypropylene.Apply a sand-blotter course.

This system does not require any rolling orfurther treatment and can be trafficked imm-ediately.

Care should be taken during constructionoperations to ensure adequate longitudinaland transverse laps where two pieces ofpolypropylene fabric are joined. Lon-gitudinal joints should be lapped a minimumof 12 inches. On a superelevated section, thelap should be laid so the top lap end is facingdownhill to help prevent water intrusionunder the membrane. On a transverse joint,the minimum overlap should beat least 24 in-ches. Additional emulsion should be on thetop side of the bottom lap to provide enoughemulsion to adhere to and waterproof the toplap. Figure 9-31, page 9-64, illustrates thisprocess on tangential sections. Applyingpolypropylene on roadway curves requirescutting and placing the fabric as shown inFigure 9-32, page 9-64. The joints in curvedareas should be overlapped a minimum of 24inches.

SELECTION OF DUST PALLIATIVEThere are many dust palliative that are ef-

fective over a wide range of soils and climaticconditions. Engineering judgment andmaterial availability play key roles in deter-mining the specific dust palliative to select.Tables 9-29 through 9-32, pages 9-65 through9-70, were developed from evaluation of theiractual perform ante to assist in the selectionprocess. The dust palliative and dust controlmethods are not listed in any order of effec-tiveness.

Where no dust palliative is listed for a par-ticular dust control method, none was found

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to be effective under those conditions. For ex-ample, for the agronomic method, a dustpalliative is not recommended for a loose,sandy soil with no binder, nor is a dust pallia-tive recommended for the surface penetrationof a firm, clay soil (see Table 9-29, page 9-65and Table 9-30, page 9-66). Also, theagronomic method of dust control is notrecommended for any traffic area (see Table9-31, page 9-67).

In Table 9-32, page 9-68 through 9-70, num-bers representing dust palliative are listedin numerical order and separated by the dust-control method. This table includes the sug-gested rates of application for each dust-palliative; for instance, gallon per squareyard for liquid spray on applications or gallonper square yard per inch for liquid (or poundper square yard per inch for powders) admixapplications.

Application RatesThe application rates should be considered

estimates, as stated above. Unfortunately,the admix method and some surface-blanketmethods represent a full commitment.Should failure occur after selection and place-ment, the only recourse is to completelyretreat the failed area, which is a lengthy andinvolved process. However, should failureoccur on a section treated with a liquid dust

palliative, retreatment of the failed area isrelatively simple, involving only a distributorand operator. A second application is en-couraged as soon as it is determined that theinitial application rate is not achieving thedesired results.

PlacementNo treatment is suggested for areas con-

taining large dense vegetation and/or largedebris. Loose soil in a wet or slurry conditionand firm soil that is wet should not be treated.Dust problems should not exist in any of theseareas; however, if the areas are known dustproducers when dry, they should be dried orconditioned and then treated.

DilutionSeveral dilution ratios are mentioned for

some liquid dust palliatives. The ratios arepresented as volume of concentrate to volumeof water and should be viewed as a necessaryprocedure before a particular liquid can besprayed. The water is a necessary vehicle toget the dust palliative on the ground. Thestated application rate is for the dust pallia-tive only. When high dilution ratios arerequired to spray a dust palliative, extra careshould be taken to prevent the mixture fromflowing into adjacent areas where treatmentmay be unnecessary and/or into drainageditches. Two or more applications may be

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necessary to achieve the desired applicationrate. Considerable time can be saved by firstdetermining the minimum dilution that per-mits a dust palliative to be sprayed.

PrewettingAll liquid dust palliative present a better

finished product when they are sprayed overan area that has been prewet with water. Theactual amount of water used in presetting anarea varies but usually ranges from 0.03 to0.15 gallons per square yard. The watershould not be allowed to pond on the surface,and all exposed soil should be completelydampened. The performance of brinematerials is enhanced by increasing theamount of water to two to three times theusual recommendation. However, the watershould not be allowed to pond, and the fine-sized particles should not be washed away.

CuringMost liquid dust palliative require a

curing period. DCA 1295 dries on the soilsurface to form a clear film. The curing timeis around 4 hours but may vary withweather conditions. Brine materials do notrequire a curing period, making them imme-diately available to traffic. Bituminousmaterials may be ready to accept traffic assoon as the material temperature drops tothe ambient temperature.

DUST CONTROL ON ROADSAND CANTONMENT AREAS

Controlling dust on roads and in andaround cantonment areas is important inmaintaining health, morale, safety, andspeed of movement. Table 9-33, page 9-72,lists several dust palliative suitable for con-trolling dust on roads and in cantonmentareas, the equipment required to apply thepalliative, the level of training required, andthe life expectancy of the dust palliative.

DUST CONTROL FOR HELIPORTSDust control for heliports is essential for

safety reasons. Because of the nature ofheliborne operations, many aircraft are likelyto be arriving or departing simultaneously.Obscuration of the airfield due to dustreduces air traffic controllers’ ability to

control flight operations and represents a sig-nificant safety hazard. Adequate dustcontrol for the heliport is essential for safeand efficient flight operations. Figure 9-33,page 9-73, illustrates heliport areas requiringdust control and lists the dimensions of theareas to be treated based on aircraft type,Table 9-34, page 9-74, lists dust palliativesuitable for use around helipads and aircraftmaintenance areas.

C0NTROL OF SANDOperation Desert Storm highlighted the

problems of stabilizing airborne and migrat-ing sand. Airborne sand reduces the lifeexpectancy of mechanical parts exposed to itsabrasive effects. From a constructionstandpoint, migrating sand poses a sig-nificant engineering problem— how toprevent dune formation on facilities.

There are many ways to control migratingsand and prevent sand-dune formation onroads, airfields, and structures. There arecertain advantages and disadvantages ineach one. The following methods for thestabilization and/or destruction of wind-borne sand dunes are the most effective:

Fencing.Paneling.Bituminous materials.Vegetative treatment.Mechanical removal.Trenching.Water.Blanket covers.Salt solutions.

These methods may be used singularly or incombination.

FencingThis method of control employs flexible,

portable, inexpensive fences to destroy thesymmetry of a dune formation. The fencedoes not need to be a solid surface and mayeven have 50 percent openings, as in snowfencing. Any material, such as wood slats,slender poles, stalks, or perforated plasticsheets, bound together in any manner and at-tached to vertical or horizontal supports isadequate. Rolled bundles that can be

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transported easily are practical. Prefabri-cated fencing is desirable because it can beerected quickly and economically. Becausethe wind tends to underscore and underminethe base of any obstacle in its flow path, thefence should be installed about 1 foot aboveground level. To maintain the effectivenessof the fencing system, a second fence shouldbe installed on top of the first fence on thecrest of the sand accumulation. The entirewindward surface of the dune should be stabi-lized with a dust-control material, such asbituminous material, before erecting the firstfence. The old fences should not be removedduring or after the addition of new fences,Figure 9-34 shows a cross section of a stabi-lized dune with porous fencing. As long as thefences are in place, the sand remains trapped.If the fences are removed, the sand soonmoves downwind, forming an advancingdune. The proper spacing and number of fen-ces required to protect a specific area can onlybe determined by trial and observation. Fig-ure 9-35 illustrates a three-fence method ofcontrol. If the supply of new sand to the dune

is eliminated, migration accelerates and dunevolume decreases. As the dune migrates, itmay move great distances downwind before itcompletely dissipates. An upwind fence maybe installed to cut off the new sand supply ifthe object to be protected is far downwind ofthe dune. This distance usually should beatleast four times the width of the dune.

PanelingSolid barrier fences of metal, wood, plastic,

or masonry can be used to stop or divert sandmovement. To stop sand, the barriers shouldbe constructed perpendicular to the winddirection. To divert sand, the panels shouldbe placed obliquely or nearly parallel to thewind. They may be a single-slant or V-shapedpattern (see Figure 9-36, page 9-76). Whenfirst erected, paneling appears to give excel-lent protection. However, panels are notself-cleaning, and the initial accumulationsmust be promptly removed by mechanicalmeans. If the accumulation is not removed,sand begins to flow over and around the

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barrier and soon submerges the object to beprotected. Mechanical removal is costly andendless. This method of control is unsatisfac-tory because of the inefficiency and expense.It should be employed only in conjunctionwith a more permanent control, such asplantings, fencing, or dust palliative. Equal-ly good protection at less cost is achieved withthe fencing method.

Bituminous MaterialsDestroying dune symmetry by spraying

bituminous materials at either the center orthe ends of the dune is an inexpensive andpractical method of sand control. Petroleumresin emulsions and asphalt emulsions are ef-fective. The desired stickiness of the sand isobtained by diluting 1 part petroleum resinemulsion with 4 parts waters and spraying atthe rate of 1/2 gallon per square yard.Generally, the object to be protected should bedownwind a distance of at least twice the tip-to-tip width of the dune. The center portion ofa barchan dune can be left untreated, or it canbe treated and unstabilized portions allowedto reduce in size by wasting. Figure 9-37shows destruction of a typical barchan duneand stabilization depending on the areatreated.

Vegetative TreatmentEstablishing a vegetative cover is an excel-

lent method of sand stabilization. Thevegetation to be established must often bedrought resistant and adapted to the climate

Soil Stabilization for Roads and Airfields 9-76

and soil. Most vegetative treatments are ef-fective only if the supply of new sand is cut off.An upwind and water, fertilizers, and mulchare used liberally. To prevent the engulfmentof vegetation, the upwind boundaries areprotected by fences or dikes, and the seed maybe protected by using mulch sprayed with abituminous material. Seed on slopes maybeanchored by mulch or matting. Oats andother cereal grasses may be planted as a fast-growing companion crop to provide protectionwhile slower-growing perennial vegetationbecomes established. Usually the procedureis to plant clonal plantings, then shrubs (as anintermediate step), followed by long-livedtrees. There are numerous suitable vegeta-tive treatments for use in differentenvironments. The actual type of vegetationselected should be chosen by qualified in-dividuals familiar with the type of vegetationthat thrives in the affected area. Stabiliza-tion by planting has the advantages ofpermanence and environmental enhance-ment wherever water can be provided forgrowth.

Mechanical RemovalIn small areas, sand maybe removed by

heavy equipment. Conveyor belts and power-driven wind machines are not recommendedbecause of their complexity and expense.Mechanical removal may be employed onlyafter some other method has been used toprevent the accumulation of more deposits.Except for its use in conjunction with another

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method of control, the mechanical removal ofsand is not practical or economical.

TrenchingA trench maybe cut either transversely or

longitudinally across a dune to destroy itssymmetry. If the trench is maintained, thedune will be destroyed by wastage. Thismethod has been used successfully in theArizona Highway Program in the YumaDesert, but it is expensive and requires con-stant inspection and maintenance.

WaterWater may be applied to sand surfaces to

prevent sand movement. It is widely usedand an excellent temporary treatment.Water is required for establishing vegetativecovers. Two major disadvantages of thismethod are the need for frequent reapplica-tion and the need for an adequate andconvenient source.

Blanket CoversAny material that forms a semipermanent

cover and is immovable by the wind serves tocontrol dust. Solid covers, though expensive,provide excellent protection and can be usedover small areas. This method of sand controlaccommodates pedestrian traffic as well as aminimum amount of vehicular traffic.Blanket covers may be made from bituminousor concrete pavements, prefabricated landing

mats, membranes, aggregates, seashells, andsaltwater solutions. After placement of anyof these materials, a spray application ofbituminous material may be required toprevent blanket decomposition and sub-sequent dust.

Salt SolutionsWater saturated with sodium chloride or

other salts can be applied to sand dunes tocontrol dust. Rainfall leaches salts from thesoil in time. During periods of no rainfall andlow humidity (below approximately 30 per-cent), water may have to be added to thetreated area at a rate of 0.10 to 0.20 gallon persquare yard to activate the salt solution.

Section IV. ConstructionProcedures

MECHANICAL SOIL STABILIZATIONThis section provides a list of construction

procedures, using mechanical stabilizationmethods, which will be useful to the engineerin the theater of operations.

On-Site BlendingOn-site blending involves the following

steps:

Preparation.Shape the area to crown and grade.

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Scarify, pulverize, and adjust themoisture content of the soil, if neces-sary.Reshape the area to crown and grade.

Addition of Imported Soil Materials. Useone of the following methods:

Distribute evenly by means of an im-proved stone spreader.Use spreader boxes behind dumptrucks.Tailgate each measured truck, load-ing to cover a certain length.Dump in equally spaced piles, thenform into windrows with a motorgrader before spreading.

Mixing.Add water, if required, to obtain amoisture content of about 2 percentabove optimum and mix with either arotary mixer, pulvimixer, blade, scari-fier, or disk.Continue mixing until the soil and ag-gregate particles are in a uniform,well-graded mass.Blade to crown and grade, if needed.

Compaction.Compact to specifications determinedby the results of a CE 55 Proctor testperformed on the blended soil ma-terial.Select the appropriate type(s) of com-paction equipment, based on the gra-dation characteristics of the blendedsoil.

Off-Site BlendingOff-site blending involves the following

steps:

Preparation. Shape area to crown andgrade.

Addition of Blended Soil Materials.Spread blended material evenly,using one of the methods discussedfor on-site blending.

Soil Stabilization for Roads and Airfields 9-78

Determine the moisture content ofthe placed, blended material. Adjustthe moisture content, if necessary.

Lime StabilizationLime stabilization involves the following

steps:

Preparation.Shape the surface to crown andgrade.Scarify to the specified depth.Partially pulverize the soil.

Spreading. Select one of the followingmethods; use about 1/2 of the total lime re-quired.

Spot the paper bags of lime on therunway, empty the bags, and levelthe lime by raking or dragging.Apply bulk lime from self-unloadingtrucks (bulk trucks) or dump truckswith spreaders.Apply the lime by slurry (1 ton of limeto 500 gallons of water). The slurrycan be mixed in a central plant or in atank truck and distributed by stand-ard water or asphalt tank trucks withor without pressure.

Preliminary Mixing, Watering, andCuring.

Mix the lime and soil (pulverize soilto less than a 2-inch particle size ex-clusive of any gravel or stone).Add water.

CAUTIONThe amount of water need to be in-creased by approximately 2 percent forlime stabilization purposes.

Mix the lime, water, and soil usingrotary mixers (or blades).Shape the lime-treated layer to theapproximate section.Compact lightly to minimize evapora-tion loss, lime carbonation, or exces-sive wetting from heavy rains.

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Cure lime-soil mixture for zero to 48hours to permit the lime and water tobreak down any clay clods. For ex-tremely plastic clays, the curingperiod may be extended to 7 days.

Final Mixing and Pulverization.Add the remaining lime by the ap-propriate method.Continue the mixing and pulveriza-tion until all of the clods are brokendown to pass a l-inch screen and atleast 60 percent of the material willpass a Number 4 sieve.Add water, if necessary, during themixing and pulverization process.

Compaction.Begin compaction immediately afterthe final mixing.Use pneumatic-tired or sheepsfootrollers.

Final curing.Let cure for 3 to 7 days.Keep the surface moist by periodicallyapplying an asphaltic membrane orwater.

Cement StabilizationCement stabilization involves the following

steps:

Preparation.Shape the surface to crown andgrade.Scarify, pulverize, and prewet thesoil, if necessary.Reshape the surface to crown andgrade.

Spreading. Use one of the followingmethods:

Spot the bags of cement on the run-way, empty the bags, and level the ce-ment by raking or dragging.Apply bulk cement from self-unloading trucks (bulk trucks) ordump trucks with spreaders.

Mixing.Add water and mix in place with arotary mixer.Perform by processing in 6- to8-foot-wide passes (the width ofthe mixer) or by mixing in a windrowwith either a rotary mixer or motorgrader.

Compaction.Begin compaction immediatelythe final mixing (no more than 1should pass between mixingcompaction), otherwise cementhydrate before compactioncompleted.

after hourand

mayis

Use pneumatic-tired and sheepsfootrollers. Finish the surface withsteel-wheeled rollers.

Curing. Use one of the following methods:Prevent excessive moisture loss byapplying a bituminous material at arate of approximately 0.15 to 0.30gallon per square yard.Cover the cement with about 2 inchesof soil or thoroughly wetted straw.

Fly-Ash StabilizationThe following construction procedures for

stabilizing soils apply to fly ash, lime-fly ashmixtures, and lime-cement-fly ash mixtures:

Preparation.Shape the surface to crown andgrade.Scarify and pulverize the soil, ifnecessary.Reshape the surface to crown andgrade.

Spreading. Use one of the following:

Spot the bags of fly ash on the road orairfield; empty the bags intoindividual piles; and distribute the flyash evenly across the surface with arake or harrow.Apply fly ash or a fly ash mixture inbulk from self-unloading trucks (bulk

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trucks) or dump trucks withspreaders.

Mixing.Begin mixing operations within 30minutes of spreading the fly ash.Mix the soil and fly ash thoroughly byusing a rotary mixer, by windrowingwith a motor grader, or by using adisk harrow.Continue to mix until the mixtureappears uniform in color.

Compaction.Add water to bring the soil moisturecontent to 2 percent above the OMC.Begin compaction immediately follow-ing final mixing. Compaction must becompleted within 2 hours of mixing.Minimum compactive effort for soilstreated with fly ash is 95 percent ofthe maximum dry density of themixed material.Reshape to crown and grade; thenfinish compaction with steel-wheeledrollers.

Curing. After the fly ash treated lifts havebeen finished, protect the surface from dryingto allow the soil material to cure for not lessthan 3 days. This maybe accomplished by—

Applying water regularly throughoutthe curing period.Covering the amended soil with a 2-inch layer of soil or thoroughly wettedstraw.Applying a bituminous material atthe rate of approximately 0.15 to 0.30gallon per square yard.

Bituminous StabilizationIn-place stabilization using bituminous

materials can be performed with a travelingplant mixer, a rotary-type mixer, or a blade.The methods for using these mixers are out-lined below:

TravelingShapwhich

Want Mixer.and compact the roadbed onthe mixed material is to be

placed. A prime coat should be ap-plied on the roadbed and allowed tocure. Excess asphalt from the primecoat should be blotted with a light ap-plication of dry sand.Haul aggregate to the job and wind-rowed by hauling trucks, a spreaderbox, or a blade.Add asphalt to the windrow by anasphalt distributor truck or addedwithin the traveling plant mixer.Use one of the several types ofsingle- or multiple-pass shaft mixersthat are available.Work the material until about 50percent of the volatiles have escaped.A blade is often used for thisoperation.Spread the aggregate to a uniformgrade and cross section.Compact.

Rotary Mixer.Prepare the roadbed as explainedabove for the traveling plant mixer.Spread the aggregate to a uniformgrade and cross section.Add asphalt in increments of about0.5 gallon per square yards and mix.Asphalt can be added within themixer or with an asphalt distributortruck.Mix the aggregate by one or morepasses of the mixer.Make one or more passes of the mixerafter each addition of asphalt.Maintain the surface to the grade andcross section by using a blade duringthe mixing operation.Aerate the mixture.

Blade Mixing.Prepare the roadbed as explainedabove for the traveling plant mixer.Place the material in a windrow.Apply asphalt to the flattenedwindrow with a distributor truck. Amultiple application of asphalt couldbe used.Mix thoroughly with a blade.Aerate the mixture.

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Move the mixed windrow to one sideof the roadway.Spread the mixture to the propergrade and crown.Compact the mixture.

Central Plant Construction MethodsAlthough central plant mixing is desirable

in terms of the overall quality of the stabilizedsoil, it is not often used for theater-of-operations construction. Stabilization withasphalt cement, however, must be ac-complished with a central hot-mix plant.

The construction methods for central plantmixing that are common for use with all typesof stabilizers are given below:

Storing.Prepare storage areas for soils andaggregates.Prepare storage area for stabilizer.Prepare storage area for water.

Mixing.Prepare the area to receive thematerials.Prepare the mixing areas.

Hauling. Use trucks.

Placing. Use a spreader box or bottom -dump truck, followed by a blade to spread to auniform thickness.

Compacting. Use a steel-wheeled,pneumatic-tired, or sheepsfoot roller,depending on the material.

Curing. Provide an asphaltic membrane forcement-stabilized soil and an asphalticmembrane or water for lime-stabilized soils.

Surface WaterproofingSurface waterproofing involves the follow-

ing steps:

Preparation.Shape the area to crown and grade.Remove all deleterious materials,such as stumps, roots, turf, andsharp-edged soil-aggregate particles.

Mixing.Adjust the water content to about op-timum to 2 percent below optimum,and mix with a traveling mixer, pul-vimixer, blade, scarifier, or plow.Blade to the crown and grade.

Compaction.Begin compaction after mixing.Use pneumatic-tired or sheepsfootrollers.

Membrane Placement.Grade the area to the crown andgrade and cut anchor ditches.Use a motor grader.Roll the area with a steel-wheeledroller or a lightweight, pneumatic-tired roller.Place a neoprene-coated nylon fabricor a polypropylene-asphalt membraneon the area.

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CHAPTER 10

Slope Stabilization

This chapter pertains to the design of earthslopes as it relates to road construction. Itparticularly concerns slope stability andwhich slopes should be used under averageconditions in cuts and embankments. Someof the subjects covered are geologic featuresthat affect slope stability, soil mechanics, in-dicators of unstable slopes, types of slopefailures, and slope stabilization.

Road failures can exert a tremendous im-pact on mission success. It is vital thatpersonnel engaged in road-building activitiesbe aware of the basic principles of slopestability. They must understand how theseprinciples are applied to construct stableroads through various geologic materialswith specific conditions of slope and soil.

Basic slope stability is illustrated by adescription of the balance of forces that existin undisturbed slopes, how these forceschange as loads are applied, and howgroundwater affects slope stability andcauses road failure.

GEOLOGIC FEATURESThere are certain geologic features that

have a profound effect on slope stability andthat can consequently affect road construc-tion in an area. Many of these geologicfeatures can be observed in the field and mayalso be identified on topographic maps andaerial photographs. In some cases, thepresence of these features may be located bycomparing geologic and topographic maps.

The following paragraphs describe geologicfeatures that have a significant effect on slopestability and the techniques that may be usedto identify them:

FaultsThe geologic uplift that accompanies moun-

tain building is evident in the mountainousregions throughout the world. Stresses builtup in layers of rock by the warping that ac-companies uplift is usually relieved byfracturing. These fractures may extend forgreat distances both laterally and verticallyand are known as faults. Often the materialon one side of the fault is displaced verticallyrelative to the other side; sometimes igneousmaterial or serpentine may be intruded intofaults. Faults are the focal point for stressrelief and for intrusions of igneous rock andserpentine; therefore, fault zones usually con-tain rock that is fractured, crushed, or partlymetamorphosed. It is extremely important torecognize that fault zones are zones ofgeologic weakness and, as such, are critical inroad location. Faults often leave topographicclues to their location. An effort should bemade to identify any faults in the vicinity of aproposed road location.

The location of these fault zones is estab-lished by looking for—

Saddles, or low sections in ridges, thatare aligned in the same general di-rection from one drainage to another.

Streams that appear to deviate fromthe general direction of the nearbystreams.

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Notice that the proposed locations of the faultzones on the topographic map follow saddlesand drainages in reasonably straight lines.

Aerial photographs should be carefully ex-amined for possible fault zones when neithergeologic maps nor topographic maps offer anyclues. An important feature of a fault zoneslide that may be detected from aerial photog-raphy is the slick, shiny surface caused by theintense heat developed by friction on slidingsurfaces within the fault zone.

Field personnel should be alert for on-the-ground evidence of faulting when neithergeologic maps nor topographic maps providedefinite clues to the location of faults.

Bedding Plane SlopeThere are many locations where sedi-

mentary or metamorphic rocks have beenwarped or tilted and the bedding planes maybe steeply sloped. If a road is planned for suchan area, it is important to determine the slopeof the bedding planes relative to the groundslope. In areas where bedding planes are ap-proximately parallel to the slope of thesidehill, road excavation may remove enough

support to allow large chunks of rock and soilto slide into the road (see Figure 10-1). Ifpreliminary surveys reveal that these condi-tions exist, then the route may need to bechanged to the opposite side of the drainagearea or ridge where the bedding planes slopeinto the hillside.

SOIL MECHANICSThe two factors that have the greatest ef-

fect on slope stability are-Slope gradient.Groundwater.

Generally, the greater the slope gradient andthe more groundwater present, the less stablewill be a given slope regardless of the geologicmaterial or the soil type. It is absolutely es-sential that engineers engaged in locating,designing, constructing, and maintainingroads understand why slope gradient andgroundwater are so important to slopestability.

Slope GradientThe effects of slope gradient on slope

stability can be understood by discussing thestability of pure, dry sand. Slope stability in

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sand depends entirely on frictional resistanceto sliding. Frictional resistance to sliding, inturn, depends on—

The slope gradient that affects theportion of the weight of an object thatrests on the surface.

The coefficient of friction.

Normal Force. The fraction of the weight ofan object that rests on a surface is known asthe normal force (N) because it acts normal to,or perpendicular to, the surface. The normalforce changes as the slope of the surface chan-ges.

The upper curve in Figure 10-2, page 10-4,shows how the gradient of a surface changesthe normal force of a 100-pound block restingon the surface. When the slope gradient iszero, the entire weight of the 100-pound blockrests on the surface and the normal force is100 pounds. When the surface is vertical,there is no weight on the surface and the nor-mal force is zero. The coefficient of frictionconverts the normal force to frictional resis-tance to sliding (F). An average value for thecoefficient of friction for sand is about 0.7.This means that the force required to slide ablock of sand along a surface is equal to 0.7times the normal force.

The lower curve in Figure 10-2, page 10-4shows how the frictional resistance to slidingchanges with slope gradient. The lower curvewas developed by multiplying the values ofpoints on the upper curve by 0.7. Therefore,when the slope gradient is zero, the normalforce is 100 pounds, and 70 pounds of force isrequired to slide the block along the surface.When the slope gradient is 100 percent, thenormal force is 71 pounds (from point 3 on theupper curve), and 50 pounds (or 71 pounds x0.7) is required to slide the block along thesurface (from point 3 on the lower curve).

Downslope Force. The portion of the weightthat acts downslope provides some of the forceto overcome frictional resistance to sliding.The downslope force, sometimes known as thedriving force, also depends on the slopegradient and increases as the gradient in-creases (see Figure 10-3, page 10-5).

Obviously, when the slope gradient becomessteep enough, the driving force exceeds thefrictional resistance to sliding and the blockslides.

Figure 10-4, page 10-6, shows the curve forfrictional resistance to sliding (from Fig-ure 10-2, page 10-4) superimposed on thecurve of the driving force (from Figure 10-3,page 10-5). These two curves intersect at 70percent (35 degree) slope gradient. In this ex-ample, this means that for slope gradientsless than 70 percent, the frictional resistanceto sliding is greater than the downslope com-ponent of the weight of the block and the blockremains in place on the surface. For slopegradients greater than 70 percent, the blockslides because the driving force is greaterthan the frictional resistance to sliding. Thisdiscussion has been confined to the case ofpure, dry sand, a case which is seldom foundin soils, but the principles of the effects ofslope gradient and frictional resistance tosliding apply to any dry soil.

Shear Strength. A block of uniform soilfails, or slides, by shearing. That is, one por-tion of the block moves past another portionin a parallel direction. The surface alongwhich this shearing action takes place iscalled the shear plane, or the plane of failure.The resistance to shearing is often referred toas shear strength. Pure sand develops shearstrength by frictional resistance to sliding;however, pure clay is a sticky substance thatdevelops shear strength because the in-dividual particles are cohesive. The presenceof clay in soils increases the shear strength ofthe soil over that of a pure sand because of thecohesive nature of the clay.

A dry clay has considerable shear strengthas demonstrated by the great force requiredto crush a clod with the fingers. However, asa dry clay absorbs water, its shear strengthdecreases because water films separate theclay particles and reduce its cohesivestrength. The structure of the clay particledetermines how much water will be absorbedand, consequently, how much the shearstrength will decrease upon saturation.There are some clays, such as illite and

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kaolinite, that provide relative stability tosoils even when saturated However, asaturated montmorillonite clay causes a sig-nificant decrease in slope stability.Saturated illite and kaolinite clays haveabout 44 percent of their total volume oc-cupied by water compared to about 97 percentfor a saturated montmorillonite clay. Thisexplains why montrnorillonite clay has such ahigh shrink-swell potential (large change involume from wet to dry) and saturated claysof this type have a low shear strength. Thus,the type of clay in a soil has a significant effecton slope stability.

Granitoid rocks tend to weather to sandysoils as the weathering process destroys thegrain-to-grain contact that holds the mineralcrystals together. If these soils remain inplace long enough, they eventually develop asignificant amount of clay. If erosion removesthe weathered material at a rapid rate, theresulting soil is coarse-textured and behavesas a sand for purposes of slope stabilityanalysis. Many soils with a significant claycontent have developed from granitoidmaterial. They have greater shear strengthand support steeper cut faces than agranitoid-derived soil with little clay.

The relative stability among soils dependson a comparison of their shear strength andthe downslope component of the weight of thesoil. For two soils developed from the samegeologic material, the soil with the higher per-centage of illite or kaolinite clay has greatershear strength than a soil with a significantamount of montmorillonite clay.

GroundwaterA common observation is that a hillslope or

the side slopes of a drainageway may be per-fectly stable during the summer but may slideafter the winter rains begin. This seasonalchange in stability is due mainly to thechange in the amount of water i n the pores ofthe soil. The effect of groundwater on slopestability can best be understood by again con-sidering the block of pure sand. Frictionalresistance to sliding in dry sand is developedas the product of the coefficient of friction andthe normal force acting on the surface of the

failure plane. A closeup view of this situationshows that the individual sand g-rains are in-terlocked, or jammed together, by the weightof the sand. The greater the force that causesthis interlocking of sand grains, the greater isthe ability to resist the shear force that iscaused by the downslope component of thesoil weight. As groundwater rises in thesand, the water reduces the normal force be-cause of the buoyant force exerted on eachsand grain as it becomes submerged.

Uplift ForceThe uplift force of the groundwater reduces

the interlocking force on the soil particles,which reduces the frictional resistance to slid-ing. The uplift force of groundwater is equalto 62.4 pounds per foot of water in the soil.The effective normal force is equal to theweight of the soil resting on the surface minusthe uplift force of the groundwater.

The following example illustrates the cal-culation of the effective normal force.

If 100 pounds of’ sand rests on ahorizontal surface and contains 3 in-ches (or 0.25 foot) of groundwater,then the effective normal force is 100- (62.4 x 0.25) = 100 - 15.6 or 84.4pounds. This shows how groundwaterreduces frictional resistance to slid-ing.The frictional resistance to slidingwith this groundwater condition is84.4 x 0.7 (average coefficient of fric-tion for sand), which equals 59.1pounds.As a comparison, for 100 pounds ofdry sand on a horizontal surface thefrictional resistance to sliding is 100 x0.7 or 70 pounds.

The following examples further emphasizehow the presence of ground water candecrease slope stability by reducing the fric-tional resistance to sliding:

First, a layer of dry sand 5 feet thickis assumed to weigh 100 pounds perfoot of depth. The downslope com-ponent of the dry weight and the fric-tional resistance to sliding for dry

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sand was calculated for various slopegradients as in Figure 10-2, page 10-4,and Figure 10-3, page 10-5.Next, 6 inches of groundwater is as-sumed to be present and the frictionalresistance to sliding is recalculated,taking into account the uplift force ofthe groundwater. The results of thesecalculations are shown in Figure 10-5.

Note: In a dry condition, sliding occurswhen the slope gradient exceeds 70 per-cent. With 6 inches of groundwater, thesoil slides when the slope gradient ex-ceeds 65 percent.

For a comparison, assume a dry sandlayer only 2 feet thick that weighs100 pounds per foot of depth. Again,assume 6 inches of groundwater andrecalculate the downslope componentof the soil weight and the frictionalresistance to sliding with and withoutthe groundwater (see Figure 10-6).

Note: With 6 inches of groundwater,this thin layer of soil slides when theslope gradient exceeds 58 percent.

These examples demonstrate that the thin-ner soil mantle has a greater potential forsliding under the same ground water condi-tions than a thicker soil mantle. The 6 inchesof groundwater is a greater proportion of thetotal soil thickness for the 2-foot soil than forthe 5-foot soil, and the ratio of uplift force tothe frictional resistance to sliding is greaterfor the 2-foot soil. A pure sand was used inthese examples for the sake of simplicity, butthe principles still apply to soils that containvarying amounts of silt and clay together withsand.

Although adding soil may decrease the ef-fect of uplift force on the frictional resistanceto sliding, it is dangerous to conclude thatslopes can be made stable solely through thisapproach. The added soil reduces uplift force,but it may increase another factor that inturn decreases frictional resistance, resultingin a slope failure. Decreasing the uplift forceof water can be best achieved through a

properly designed groundwater control sys-tem.

Seepage ForceThere is still another way that ground-

water contributes to slope instability, andthat is the seepage force of groundwater as itmoves downslope. The seepage force is thedrag force that moving water exerts on eachindividual soil particle in its path. Therefore,the seepage force contributes to the drivingforce that tends to move masses of soildownslope. The concept of the seepage forcemay be visualized by noting how easily por-tions of a coarse-textured soil may bedislodged from a road cut bank when the soilis conducting a relatively high volume ofgroundwater.

SLOPE FAILURESlope failure includes all mass soil move-

ments on—Man-made slopes (such as road cuts

and fills).Natural slopes (in clear-cut areas or

undisturbed forest).

A classification of slope failure is useful be-cause it provides a common terminology, andit offers clues to the type of slope stabilityproblem that is likely to be encountered.Types of slope and road failures areremarkably consistent with soils, geologicmaterial, and topography. For example, fast-moving debris avalanches or slides develop inshallow, coarse-textured soils on steephillsides; large, rotational slumps occur indeep, saturated soils on gentle to moderateslopes.

Rockfalls and RockslidesRockfalls and rockslides usually originate

in bedded sediments, such as massivesandstone, where the beds are undercut bystream erosion or road excavation. Stabilityis maintained by the—

Competence of the rock.Frictional resistancethe bedding planes.

to sliding along

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These factors are particularly importantwhere the bedding planes dip downslopetoward a road or stream. Rockslides occursuddenly, slide with great speed, and some-times extend entirely across the valleybottom. Slide debris consists of fracturedrock and may include some exceptionallylarge blocks. Road locations through areaswith a potential for rockslides should be ex-amined by specialists who can evaluate thecompetence of the rock and determine the dipof the bedding planes.

Debris Avalanches and Debris FlowsThese two closely related types of slope

failure usually originate on shallow soils thatare relatively low in clay content on slopesover 65 percent. In southeast Alaska, the USForest Service has found that debrisavalanches develop on slopes greater than 65percent on shallow, gravelly soils and thatthis type of slope failure is especially frequenton slopes over 75 percent.

Debris avalanches are the rapid downslopeflowage of masses of loose soil, rock, andforest debris containing varying amounts ofwater. They are like shallow landslidesresulting from frictional failure along a slipsurface that is essentially parallel to thetopographic surface, formed where the ac-cumulated stresses exceed the resistance toshear. The detached soil mantle slidesdownslope above an impermeable boundarywithin the loose debris or at the unweatheredbedrock surface and forms a disarrangeddeposit at the base. Downslope, a debrisavalanche frequently becomes a debris flowbecause of substantial increases in water con-tent. They are caused most frequently whena sudden influx of water reduces the shearstrength of earth material on a steep slope,and they typically follow heavy rainfall.

There are two situations where these typesof slope failure occur in areas with shallowsoil, steep slopes, and heavy seasonal rainfall.

The first situation is an area where streamdevelopment and geologic erosion haveformed high ridges with long slopes and

steep, V-shaped drainages, usually in beddedsedimentary rock. The gradient of many ofthese streams increases sharply from themain stream to the ridge; erosion has createdheadwalls in the upper reaches. The bowl-shaped headwall region is often the junctionfor two or more intermittent stream channelsthat begin at the ridgetop. This leads to aquick rise in ground water levels duringseasonal rains. Past debris avalanches mayhave scoured round-bottom chutes, ortroughs, into the relatively hard bedrock.The headwall region may be covered withonly a shallow soil mantle of precariousstability, and it may show exposed bedrock,which is often dark with ground waterseepage.

The second situation with a high potentialfor debris avalanches and flows is where ex-cavated material is sidecast onto slopesgreater than 65 percent. The sidecastmaterial next to the slope maintains stabilityby frictional resistance to sliding and bymechanical support from brush and stumps.As more material is sidecast, the brush andstumps are buried and stability is maintainedsolely by frictional resistance to sliding.Since there is very little bonding of thismaterial to the underlying rock, the entireslope is said to be overloaded. It is quite com-mon for new road fills on steep overloadedslopes to fail when the seasonal rainssaturate this loose, unconsolidated material,causing debris avalanches and flows. Underthese circumstances, the road fill, togetherwith a portion of the underlying naturalslope, may form the debris avalanche (seeFigure 10-7).

Debris avalanches and debris flows occursuddenly, often with little advance warning.There is practically nothing that can be doneto stabilize a slope that shows signs of an im-pending debris avalanche. The best possibletechnique to use to prevent these types ofslope failures is to avoid—

Areas with a high potential for debrisavalanches.Overloading steep slopes with exces-sive sidecast.

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Engineers should learn the vegetative andsoil indicators of this type of unstable terrain,especially for those areas with high seasonalgroundwater levels.

If unstable terrain must be crossed byroads, then radical changes in road grade androad width may be required to minimize sitedisturbance. Excavated material may needto be hauled away to keep overloading of un-stable slopes to an absolute minimum. Thelocation of safe disposal sites for this materialmay be a serious problem in steep terrainwith sharp ridges. Site selection will requirejust as much attention to the principles ofslope stability as to the location and construc-tion of the remainder of the road.

Slumps and EarthflowsSlumps and earthflows usually occur in

deep, moderately fine- or fine-textured soilsthat contain a significant amount of siltand/or clay. In this case, shear strength is acombination of cohesive shear strength andfrictional resistance to sliding. As noted ear-lier, groundwater not only reduces frictionalresistance to shear, but it also sharplyreduces cohesive shear strength. Slumps areslope failures where one or more blocks of soil

have failed on a hemispherical, or bowl-shaped, slip surface. They may show varyingamounts of backward rotation into the hill inaddition to downslope movement (see Figure10-8, page 10-12). The lower part of a typicalslump is displaced upward and outward like abulbous toe. The rotation of the slump blockusually leaves a depression at the base of themain scarp. If this depression fills with waterduring the rainy season, then this feature isknown as sag pond. Another feature of largeslumps is the “hummocky” terrain, composedof many depressions and uneven ground thatis the result of continued earthflow after theoriginal slump. Some areas that are under-lain by particularly incompetent material,deeply weathered and subject to heavy winterrainfall, show a characteristically hummockyappearance over the entire landscape. Thisjumbled and rumpled appearance of the landis known as melange terrain.

Depressions and sag ponds allow winterrains to enter the ground water reservoir,reduce the stability of the toe of the slump,and promote further downslope movement ofthe entire mass. The mature timber thatusually covers old slumps often contains“jackstrawed, ” or “crazy,” trees that lean at

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many different angles within the stand. Thisindicates unstable soils and actively movingslopes (see Figure 10-9).

There are several factors affecting slumpsthat need to be examined in detail to under-stand how to prevent or remedy this type ofslope failure. The block of soil that is subjectto slumping can be considered to be resting ona potential failure surface of hemisphericalshape (see Figure 10-10). The block is moststable when its center of gravity is at itslowest position on this failure surface. Whenthe block fails, its center of gravity is shiftedto a lower, more stable position as a result ofthe failure. Added weight, such as a road fill,at the head of a slump shifts the center ofgravity of the block to a higher, more unstableposition and tends to increase the potentialfor rotation. Similarly, removing weight fromthe toe of the slump, as in excavating for aroad, also shifts the center of gravity of theblock to a higher position on the failure sur-face. Therefore, loading the head of a slumpand/or unloading the toe will increase thepotential for further slumping on short slopes(see Figure 10-11). The chance of slumpingcan be reduced by shifting the center ofgravity of a potential slump block to a lowerposition by following the rule: Unload thehead and load the toe.

If it is absolutely necessary to locate a roadthrough terrain with a potential for slump-ing, there are several techniques that may beconsidered to help prevent slumps andearthflows. They are—

Improve the surface drainage.Lower the groundwater level.Use rock riprap, or buttresses, to pro-vide support.Install an interceptor drain.Compact fills.

Surface Drainage. Improving the surfacedrainage is one of the least expensive andmost effective techniques, but it is often over-looked. Sag ponds and depressions can beconnected to the nearest stream channel withditches excavated by a bulldozer or a grader.Figure 10-12, page 10-14, shows the theoreti-cal effect on the groundwater reservoir of asurface drainage project. Improved drainageremoves surface water quickly, lowers thegroundwater level, and helps stabilize theslump.

Groundwater Level. Lower the ground-water level by means of a perforated pipe thatis augered into the slope at a slight upward

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angle. These drains are usually installed inroad cutbanks to stabilize areas above an ex-isting road or below roads to stabilize fills.Installing perforated pipe is relatively expen-sive, and there is a risk that slight shifts inthe slump mass may render the pipe ineffec-tive. In addition, periodic cleaning of thesepipes is necessary to prevent blockage byalgae, soil, or iron deposits.

Rock Riprap, or Buttresses. Stabilize ex-isting slumps and prevent potential slumpsby using rock riprap, or buttresses, to providesupport for road cuts or fills (see Figure 10-13,page 10-15). Heavy rock riprap replacesthe stabilizing weight that is by excavationduring road construction (see Figure 10-11).Another feature of riprap is that it is porousand allows groundwater to drain out of the

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slump material while providing support forthe cut slope.

Interceptor Drain. Install an interceptordrain to collect groundwater that is movinglaterally downslope and under the road,saturating the road fill. A backhoe can beused to install interceptor drains in the ditchalong an existing road. Figure 10-14 shows asample installation.

Fills. Compact fills to reduce the risk of roadfailure when crossing small drainages. Comp-action increases the density of the material,reduces the pore space, and thereby reducesthe adverse effect of ground water. The foun-dation material under the proposed fill

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should be evaluated as part of the designprocess to determine if this material will sup-port a compacted fill without failure. Roadsmay often be built across gentle slopes of in-competent material with a high groundwatertable by overexcavating the material, placinga thick blanket of coarse material, then build-ing the road on the blanket (see Figure 10-15,page 10-16). The coarse rock blanket dis-tributes the weight of the roadway over alarger area and provides better drainage forgroundwater under the road.

Soil CreepMany of these slope failures may be

preceded and followed by soil creep, a rela-tively slow-moving type of slope failure. Soil

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creep may be a continuous movement on theorder of less than 1 foot per decade. The in-dicators of soil creep may be subtle, but youmust be aware of the significance of this typeof slope failure. Soil creep, at any moment,may be immeasurable; however, when the ef-fect is cumulated over many years, it cancreate stresses within the soil mantle thatmay approach the limit of frictional resis-tance to sliding and/or the cohesive shearstrength along a potential shear failure sur-face.

Soil creep is particularly treacherous inconjunction with debris avalanches. Thebalance between stability and failure may beapproached gradually over a number of yearsuntil only a heavy seasonal rain or a minordisturbance is necessary to trigger acatastrophic slope failure. Soil creep alsobuilds up stresses in potential slumps so thateven moderate rainfall may start a slowearthflow on a portion of the slope. Depend-ing on the particular conditions, minormovement may temporarily relieve thesestresses and create sags or bulges i n the slope;or it may slightly steepen the slope and in-crease the potential for a major slump duringthe next heavy rain. The point to rememberis that soil creep is the process that slowlychanges the balance of forces on slopes. Eventhough an area may be stable enough towithstand high seasonal groundwater levelsthis year, it may not be able to 5 years fromnow.

STABLE SLOPE CONSTRUCTIONIN BEDDED SEDIMENTS

Construction of stable roads requires notonly a basic understanding of regional geol-ogy and soil mechanics but also specific,detailed information on the characteristics of

soils, groundwater, and geology where theroad is to be built. This following paragraphspresent techniques on road location and thesoil and vegetative indicators of slope in-stability and high groundwater levels.

Bedded sediments vary from soft siltstoneto hard, massive sandstone. These differentgeologic materials, together with geologicprocesses and the effect of climate acting overlong periods of time, determine slopegradient, soil, and the rate of erosion. Thesefactors also determine the particular type ofslope stability problem that is likely to be en-countered. There are four slope stabilityproblems associated with distinctive siteswithin the bedded sediments. They are—

Sandstone - Type I.Sandstone - Type II.Deeply weathered siltstone.Sandstone adjoining ridges of igneousrock.

Sandstone - Type IType I sites are characterized by sharp

ridges with steep slopes that may show auniform gradient from near the ridgetop tothe valley bottom. The landscape is sharplydissected by numerous stream channelsthat may become extremely steep asthey approach the ridgetop. Headwalls(bowl-shaped areas with slope gradients often100 percent or greater) may be present in theupper reaches of the drainage. The headwallis usually the junction for several intermit-tent streams that can cause sharp rises in thegroundwater levels in the soil mantle duringwinter storms. It is quite common to notegroundwater seepage on exposed bedrock inthe headwall even during the summer. Fig-ure 10-16 shows a block diagram that

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illustrates the features of Type I sites. Thisarea was taken from the topographic mapof the upper Smith River in Oregon (Figure10-17, page 10-18).

The soils on the most critical portions ofType I sites are coarse-textured and shallow(less than 20 inches to bedrock). These soilsare considered to be unstable on slopesgreater than 80 percent. In areas wheregroundwater is present, these soils are con-sidered to be unstable on slopes considerablyless than 80 percent.

Debris avalanches and debris flows are themost common slope failure on Type I sites,and the headwall region is the most likelypoint of origin for these failures. Road con-struction through headwalls causesunavoidable sidecast. The probability is highfor even minimum amounts of sidecast tooverload slopes with marginal stability and tocause these slopes to fail. Observers oftencomment on the stability of full bench roadsbuilt through headwalls without realizingthat debris avalanches may have occurredduring construction before any traffic movedover the road.

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Unstable-Slope Indicators. There are cer-tain indicators of unstable slopes in Type Isites that may be used during road location.They are—

Pistol-butted trees (see .Figure 10-18).Sliding soil or debris or active soilcreep caused these trees to tipdownslope while they were small. Asthe tree grew, the top regained a ver-tical posture. Pistol-butted trees area good indicator of slope instabilityfor areas where rain is the major com-ponent of winter precipitation; how-ever, deep, heavy snow packs at highelevations may also cause this samedeformation.Tipped trees (see Figure 10-19).These trees have a sharp angle in thestem. This indicates that the treegrew straight for a number of yearsuntil a small shift in the soil mantletipped the tree. The angled stem isthe result of the recovery of verticalgrowth.

Tension cracks (see Figure 10-20).Soil creep builds up stresses in thesoil mantle that are sometimes re-lieved by tension cracks. These fea-tures may be hidden by vegetation,but they definitely indicate active soilmovement.

Road-Location Techniques. Techniquesfor proper road location on Type I sites in-clude the following:

Avoid headwall regions. Ridgetop lo-cations are preferred rather thancrossing through headwall regions.Roll the road grade. Avoid headwallsor other unstable areas by rolling theroad grade. Short, steep pitches ofadverse and favorable grade may beincluded,

Construction Techniques. Consider thefollowing techniques when roads must be con-structed across long, steep slopes or aboveheadwall regions where sidecast must beheldto a minimum:

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Reduce the road width. This mayrequire a small tractor with a morenarrow blade (for example, a D6) forconstruction. A U-shaped blade re-sults in less sidecast than a straightblade, possibly because of better con-trol of loose material.Control blasting techniques. Thesetechniques may be used to reduce over-breakage of rock and reduce theamount of fractured material that isthrown out of the road right-of-wayand into stream channels.Remove material. Hauling excavatedmaterial away from the steepestslopes may be necessary to avoidoverloading the lower slopes.

Select safe disposal sites. Disposalsites for excavated material should bechosen with care to avoid overloadinga natural bench or spur ridge, causingslope failure (see Figure 10-21, page10-20). The closest safe disposal sitemay be a long distance from the con-struction site but the additional haul-ing costs must be weighed against thedamage caused by failure of a closerdisposal site with a higher probabilityof failure.Fill saddles. Narrow saddles may beused to hold excess material by firstexcavating bench roads below and oneach side of the saddle. The saddlemay then be flattened and the loose

Figure 10-20. Tension cracks.

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material that rolls downslope will becaught by the benches. Excavatedmaterial may be compacted on theflattened ridge to buildup the grade.Choose the correct culvert size. A cul-vert should carry the maximum es-timated flow volume for the designstorm.Protect slopes. Culverts must not dis-charge drainage water onto the baseof a fill slope. Culverts should eitherbe designed to carry water on thenatural grade at the bottom of the fillor downspouts or half-round culvertsshould be used to conduct water fromthe end of shorter culverts down thefill slope to the natural channel.

Sandstone - Type IIType II sites have slopes with gradients

that range from less than 10 percent up to 70or 80 percent. The longer slopes may bebroken by benches and have rounder ridges,fewer drainages, and gentler slope gradientsthan those on Type I sites. Headwalls arerare, and small patches of exposed bedrockare only occasionally found on the steeperslopes.

The soils on the gentle slopes developedover many centuries and are deep (often

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greater than 40 inches), with a clay content ashigh as 50 to 70 percent. The soils on thesteeper slopes may be as deep as 40 inches,but the bedrock is fractured and weathered sothere is a gradual transition from the soil intothe massive bedrock. It is these factors ofdeeper soils, higher clay content, gentlerslopes, and a gradual transition to bedrockthat makes this terrain more stable than theterrain on Type I sites.

The factors that characterize Type II sitesalso cause this terrain to have more slopefailures due to slumps and earthflows. Themost unstable portions of Type II sites are thesteep, concave slopes at the heads ofdrainages, the edge of benches, or the loca-tions where ground water tends toaccumulate. Road failures frequently involvepoorly consolidated or poorly drained roadfills and embankments greater than 12 to 15feet on any of the red clayey soils. Soil creepalso creates tension within the clayey soils atthe convex ridge nose where slope gradientsmay be onfy 50 percent. Excavation for roadsat these points of sharp slope convexity some-times causes failure of the embankment.

Unstable-Slope Indicators. Vegetative in-dicators of unstable portions of the landscapeinclude mature trees that tip or lean as aresult of minor earthflow or soil creep on thesteeper slopes. Tipped or leaning trees mayalso be found on poorly drained soils adjacentto the stream channels. Actively movingslopes may show tension cracks, particularlyon the steeper slopes.

There are several good indicators that maybe used to determine the height thatgroundwater may rise in the soil and roughlyhow long during the year that the soilremains saturated. Iron compounds withinthe soil profile oxidize and turn rusty red orbright orange and give the soil a mottled ap-pearance when the groundwater rises andfalls intermittently during the winter. Thedepth below the soil surface where these mot-tles first occur indicates the averagemaximum height that this fluctuating watertable rises in the soil. At locations where the

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water table remains for long periods duringthe year, the iron compounds are chemicallyreduced and give the soil profile a gray orbluish-gray appearance. The occurrence ofthese gleyed soils indicates a soil that issaturated for much of the year. Occasionally,mottles may appear above a gleyed subsoil,which indicates a seasonally fluctuatingwater table above a subsoil that is subject toprolonged saturation. Engineers should beaware of the significance of mottled andgleyed soils that are exposed during road con-struction. These indicators give clues to theneed for drainage or extra attention concern-ing the suitability of a subsoil for foundationmaterial.

Road-Location Techniques. Techniquesfor locating stable roads on Type II sites in-clude the following

Avoid steep concave basins. Do notlocate roads through these areaswhere stability is questionable, as in-dicated by vegetation and topography.Ridgetop locations are preferred.Choose stable benches. Benches mayoffer an opportunity for location ofroads and landings, but these benchesshould be examined carefully to seethat they are supported by rock andare not ancient, weathered slumpswith marginal stability.Avoid cracked soil. Avoid locating aroad around convex ridge noses orbelow the edge of benches where ten-sion cracks or catsteps indicate a highprobability for embankment failure.

Construction Techniques. Certain designand construction practices should be con-sidered when building roads in this terrain.

Avoid overconstruction. If it is neces-sary to build a road across steepdrainages, avoid overconstruction andhaul excess material away to avoidoverloading the slopes.Avoid high cut embankments. An en-gineer or soil scientist may be able tosuggest a maximum height at theditch line for the particular soil andsituation. A rule-of-thumb estimate

for maximum height for a cut bank indeep, clayey soils is 12 to 15 feet.Pay special attention to fills. Fills ofclayey material over steep stream cross-ings may fail if the material is notcompacted and if groundwater sat-urates the base of the fill. Fill failuresin this wet, clayey material on steepslopes tend to move initially as aslump, then may change to a mudflowdown the drainage. To avoid this,compact the fill to accepted engineer-ing standards, paying special atten-tion to proper lift thicknesses, mois-ture content, and foundation condi-tions. Also, design drainage features,where necessary, to control ground-water in the base of a fill. For ex-ample, consider either a perforatedpipe encased in a crushed rock filteror a blanket of crushed rock underthe entire fill.

Deeply Weathered SiltstoneThis stability problem originates in

siltstone that is basically incompetent andeasily weathered. Slumps and earthflows,both large and small, are very common whenthis material is subjected to heavy winterrainfall. The landscape may exhibit a benchyor hummocky appearance. Slopes withgradients as low as 24 percent may be con-sidered unstable in deeply weatheredsiltstone with abundant water.

Unstable-Slope Indicators. Vegetativeand topographic indicators of slope instabilityare numerous. Large patches of plants asso-ciated with set soils indicate high ground-water levels and impeded drainage. Conifersmay tip or lean due to earthflow or soil creep.Slumps cause numerous benches, some ofwhich show sag ponds. Blocks of soil may sagand leave large cracks, which gradually fill inwith debris and living vegetation. The sharpcontours of these features soften in time untilthe cracks appear as “blind drainages” or sec-tions of stream channel that are blocked atboth ends. The cracks collect water, keep thegroundwater reservoir charged, and con-tribute to active soil movement.

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Road-Location Techniques. Techniquesfor locating stable roads through terrain thathas been derived from deeply weatheredsilt-stone include the following

Check for indicators of groundwater.Avoid locating roads through areaswhere groundwater levels are highand where slope stability is likely tobe at its worst. Such locations may beindicated by hydrophytes, tipped orleaning trees, and mottled or gleyedsoils.Consider ridges. Ridgetop locationsmay be best because groundwaterdrainage is better there. Also, the un-derlying rock may be harder and mayprovide more stable roadbuildingmaterial than weathered siltstone.Ensure adequate reconnaissance.Take pains to scout the terrain awayfrom the proposed road location,using aerial photos and ground recon-naissance to be sure that the line doesnot run through or under an ancientslump that may become unstable dueto the road construction.

Construction Techniques. Special roaddesign and construction techniques for thistype of terrain may include the following

Drainage ditches. Every effort shouldbe made to improve drainage, bothsurface and subsurface, since ground-water is the major factor contributingto slope instability for this material.Sag ponds and bogs may be drainedwith ditches excavated by tractor orwith ditching dynamite.Culverts. Extra culverts should beused to prevent water from pendingabove the road and saturating theroad prism and adjacent slopes.Road ditches. They should be careful-ly graded to provide plenty of fall tokeep water moving. A special effortshould be made to keep ditches andculverts clean following con-struction.

Slope Stabilization 10-22

Sandsone Adjoining Ridgesof Igneous Rock

This slope stability problem in bedded sedi-ments is caused by remnants of sandstoneadjoining ridges of igneous rock. As a generalrule, any contact zone between sedimentarymaterial and igneous material is likely tohave slope stability problems.

Unstable-Slope Indicators. The igneousrock may have caused fracturing and partialmetamorphosis of the sedimentary rock atthe time of intrusion. Also, water is usuallyabundant at the contact zone because the igneous material is relatively impermeablecompared to the sediments; therefore, thesedimentary rock may be deeply weathered.

Road-Location Techniques. Special roadlocation techniques for this type of slopestability problem include the following

Pay attention to the contact zone.Examine the terrain carefully on theground and on aerial photos todetermine if the mass of sandstone islarge or small relative to the igneousrock mass. If the sandstone is in theform of a relatively large spur ridge,then the contact zone deserves specialattention. The contact zone should becrossed as high as possible wheregroundwater accumulation is at aminimum. Elsewhere on the ridge ofsandstone, the stabilty problems arethe same as for Type I or Type IIsandstone.Consider an alternative location. Ifthe remnant of sandstone is relativelysmall, such as a ridge nose, then theentire mass of sandstone may becreeping rapidly enough to be con-sidered unstable and the road shouldbe located above this material in themore stable igneous rock.

Construction Techniques. Design andconstruction techniques to be considered areas follows:

Avoid high embankments. The sedi-mentary rock in the contact zone is

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likely to be fractured and may besomewhat metamorphosed as a resultof the intrusion of igneous rock. In ad-dition, the accumulation of ground-water is likely to have caused ex-tensive weathering of this material.The road cut height at the ditch lineshould be kept as low as possiblethrough this zone. Support by rock

riprap may be necessary if the cutembankment must be high.Ensure good drainage. It is good apractice to put a culvert at the contactzone with good gradient on theditches to keep the contact zone welldrained. Other drainage measures,such as drain tile or perforated pipe,may be necessary.

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CHAPTER 11

G e o t e x t i l e s

Other techniques are available for improv-ing the condition of a soil besides mechanicalblending and chemical stabilization. Thesetechniques incorporate geotextiles in variouspavement applications.

The term geotextile refers to any permeabletextile used with foundation, soil, rock, earth,or any other geotechnical engineering-relatedmaterial as an integral part of a human-madeproject, structure, or system. Geotextiles arecommonly referred to as geofabrics, engineer-ing fabrics, or just fabrics.

APPLICATIONSGeotextiles serve four primary functions:

Reinforcement.Separation.Drainage.Filtration.

In many situations, using these fabrics canreplace soil, which saves time, materials, andequipment costs. In theater-of-operationshorizontal construction, the primary concernis with separating and reinforcing low load-bearing soils to reduce construction time.

ReinforcementThe design engineer attempts to reduce the

thickness of a pavement structure wheneverpossible. Tests show that for low load-bearing soils (generally 5), the use ofgeofabrics can often decrease the amount ofsubbase and base course materials required.The fabric lends its tensile strength to the soil

to increase the overall design strength. Fig-ure 11-1, shows an example of this concept.

Swamps, peat bogs, and beach sands canalso be quickly stabilized by the use ofgeofabrics. Tank trails have been success-fully built across peat bogs using commercialgeofabric.

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SeparationConstruction across soft soils creates a

dilemma for the engineer. The constructionproceeds at a slow pace because much time isspent recovering equipment mired in muckand hauling large quantities of fill to provideadequate bearing strength. Traditionally,the following options may be considered:

Bypass the area.Remove and replace the soil.Build directly on the soft soil.Stabilize mechanically or with an ad-mixture.

Bypass. This course of action is often ne-gated by the tactical situation or other physi-cal boundaries.

Remove and Replace. Commonly referredto as “mucking,” this option is sometimes avery difficult and time-consuming procedure.It can only be used if the area has good, stablesoil underneath the poor soil. Furthermore, asuitable fill material must be found nearby.

Build On Directly. Base course construc-tion material is often placed directly on theweak soil; however, the base course layer isusually very thick and the solution is tem-porary. A “pumping” action causes fines tointrude into the base course, which causes thebase course to sink into the weak soil (see Fig-ure 11-2). As a result, the base course itselfbecomes weak. The remedy is to dump morematerial on the site.

Geotextiles 11-2

Stabilize. As discussed in Chapter 10,stabilizing can be done mechanically or withan admixture could be used, but it may bevery time consuming and costly.

For the last three options, the poor soileventually intrudes into the base course, suchas in a swampy area, or simply moves underthe loads. By using geofabrics, the poor soilscan be separated and confined to prevent in-trusion or loss of soil (see Figure 11-3).

DrainageGeotextiles placed in situations where

water is transmitted in the plane of theirstructure provide a drainage junction. Ex-amples are geotextiles used as a substitute forgranular material in trench drains, blanketdrains, and drainage columns next to struc-tures. This woven fabric offers poor drainagecharacteristics; thick nonwoven fabrics haveconsiderably more void space in their struc-ture available for water transmission. A gooddrainage geotextile allows free water flow(but not soil loss) in the plane of the fabric.

FiltrationIn filter applications, the geotextile is

placed in contact with soil to be drained andallows water and any particles suspended inthe water to flow out of the soil while prevent-ing unsuspended soil particles from beingcarried away by the seepage. Filter fabricsare routinely used under riprap in coastal,river, and stream bank protection systems toprevent bank erosion. Another example ofusing a geotextile as a filter is a geotextile-lined drainage ditch along the edge of a roadpavement.

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UNPAVED AGGREGATEROAD DESIGN

The widespread acceptance of geotextilesfor use in engineering design has led to aproliferation of geotextile manufacturers anda multitude of geofabrics, each with differentengineering characteristics. The designguidelines and methodology that follow willassist in selecting the right geofabric to meetconstruction requirements.

Site ReconnaissanceAs with any construction project, a site

reconnaissance provides the designer insightinto the requirements and the problems thatmight be encountered during construction.

Subgrade Soil Type and StrengthIdentify the subgrade soil and determine

its strength as outlined in Chapter 9. If pos-sible, determine the soil’s shear strength (C)in psi. If you are unable to determine C, usethe nomograph in Figure 11-4 to convert theCBR value or Cone Index to C.

Subgrade Soil Permissible LoadThe amount of load that can be applied

without causing the subgrade soil to fail isreferred to as the permissible stress (S).

Permissible subgrade stress without ageotextile:

S = (2.8) C

Permissible subgrade stress with ageotextile:

S = (5.0) C

Wheel Load, Contact Pressure,and Contact Area

Estimate wheel load, contact pressure, andcontact area dimensions (see Table 11-1, page11-4). For the purpose of geotextile design,both single and dual wheels are represented

as single-wheel loads (L) equal to one-half theaxle load. The wheel load exerted by a singlewheel is applied at a surface contact pressure(P) equal to the tire inflation pressure. Dualwheel loads apply a P equal to 75 percent of

the tire inflation pressure. Tandem axlesexert 20 percent more than their actualweight to the subgrade soil due to overlappingstress from the adjacent axle in the tandemset.

Estimate the area being loaded (B2):

B = = length of one side of the squarecontact area

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Aggregate Base Thickness Using the calculated values of X andAssuming that wheel loads will be applied X geotextile, use Table 11-2 to find

over a square area, use the Boussinesq theory the corresponding value of M and Mof load distribution to determine the ag- geotextile.gregate section thickness required to support Then solve for the aggregate basethe design load. The Boussinesq theory coef-ficients are found in Table 11-2. thickness H and H geotextile.

First, solve for X: Without a geotextile:SWithout a geotextile: X = —

(4)P With a geotextile:With a geotextile:

S geotextile H geotextile =X geotextile = (4) P

H=

B

B (inches)(2) M

(2) M geotextile

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The difference between H and H geotextileis the aggregate savings due to the geotextile.

Aggregate Quality. Adjust the aggregatesection thickness for aggregate quality. Thedesign method is based on the assumptionthat a good quality of aggregate (with a min-imum CBR value of 80) is used. If a lowerquality is used, the aggregate section thick-ness must be adjusted.

Table 11-3, page 11-6, contains typical com-pacted strength properties of commonstructural materials. These values are ap-proximations; use more specific data if it isavailable. Extract the appropriate thicknessequivalent factor from Table 11-3, page 11-6,then divide H by that factor to determine theadjusted aggregate section thickness.

Service Life. Adjust the aggregate basethickness for the service life. The designmethod assumes that the pavement will besubjected to one thousand 18,000-poundequivalent vehicle passes. If you anticipatemore than 1,000 equivalent passes, you willneed to increase the design thickness by 30percent and monitor the performance of theroad.

A second method of determining minimumrequired cover above a subgrade for wheeledvehicles with and without a geotextile re-quires fewer input parameters. Again, useFigure 11-4, page 11-3, to correct CBR or coneindex values to a C value. Determine the per-missible stress (S) on the subgrade soil bymultiplying C times 2.8 without a geotextileand 5.0 with a geotextile. Select the heaviestvehicle using the road and the design vehiclefor each wheel load configuration: single,dual, or tandem. Using the appropriategraph (see Figures 11-5, 11-6, or 11-7, pages11-7 and 11-8) enter the graph at S. Roundthe design-vehicle wheel loads to the nexthigher wheel-load weight curve (for example,a dual wheel load of 10,500 pounds is roundedto 12,000 pounds (see Figure 11-6, page 11-7)).Determine the intersection between the ap-propriate wheel-load curve and S (with andwithout a geotextile) then read the minimumrequired thickness on the left axis. Use thegreatest thickness values as the design thick-ness with and without a geotextile. Corn parethe cost of the material saved with the cost ofthe geotextile to determine if using thegeotextile is cost effective.

SELECTING A GEOTEXTILEUp to this point in the geotextile design

process, we have been concerned with generaldesign properties for designing unpaved ag-gregate roads. Now you must decide which

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geotextile fabric best meets your project re-quirements.

There are two major types of geotextilefabric: woven and nonwoven. Woven fabricshave filaments woven into a regular, usuallyrectangular, pattern with openings that arefairly evenly spaced and sized. Nonwovenfabrics have filaments connected in a methodother than weaving, typically needle punch-ing or head bonding at intersection points ofthe filaments. The pattern and the spacingand size of the openings are irregular in non-woven fabrics. Woven fabrics are usuallystronger than nonwoven fabrics of the samefabric weight. Woven geotextiles typicallyreach peak strength at between 5 and 25 per-cent strain. Nonwoven fabrics have a highelongation of 50 percent or more at maximumstrength.

Table 11-4, page 11-9, provides informationon important criteria and principle propertiesto consider when selecting or specifying ageotextile for a particular application. Thetype of equipment used to construct the roador airfield pavement structure on top of thegeotextile must be considered. Equipmentground pressure (in psi) is an important fac-tor in determining the geotextile fabricthickness. A thicker fabric is necessary tostand up to high equipment ground pressure(see Table 11-5, page 11-10).

Once the required degree of geotextile sur-vivability is determined, minimum specifi-cation requirements can be established basedon ASTM standards (see Table 11-6, page11-10). After determining the set of testingstandards the geotextile will be required to

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withstand to meet the use and constructionrequirements, either specify a geotextile forordering or evaluate on-hand stock.

Roadway ConstructionThere is no singular way to construct with

geofabrics. However, there are several ap-plications and general guidelines that can beused.

Prepare the Site. Clear, grub, and excavatethe site to design grade, filling in ruts and sur-face irregularities deeper than 3 inches (seeFigure 11-8, page 11-11 ). Lightly compact thesubgrade if the soil is CBR 1. The light com-paction aids in locating unsuitable materialsthat may damage the fabric. Remove thesematerials when it is practical to do so.

When constructing over extremely softsoils, such as peat bogs, the surface materials,such as the root mat, may be advantageousand should be disturbed as little as possible.Use sand or sawdust to cover protruding

roots, stumps, or stalks to cushion the geotex-tile and reduce the potential for fabricpuncture. Nonwoven geotextiles, with theirhigh elongation properties, are preferredwhen the soil surface is uneven.

Lay the Fabric. The fabric should be rolledout by hand, ahead of the backfilling anddirectly on the soil subgrade. The fabric iscommonly, but not always, laid in the direc-tion of the roadway. Where the subgradecross section has large areas and leveling isnot practical, the fabric may be cut and laidtransverse to the roadway. Large wrinklesshould be avoided. In the case of wide roads,multiple widths of fabric are laid to overlap.The lap length normally depends on the sub-grade strength. Table 11-7, page 11-12, pro-vides general guidelines for lap lengths.

Lay the Base. If angular rock is to form thebase, it is a common procedure to first place aprotective layer of 6 to 8 inches of finermaterial. The base material is then dumpeddirectly onto the previously spread load,

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pushed out over the fabric, and spread from 11-13, shows one method that can be adaptedthe center using a bulldozer. It is critical thatthe vehicles not drive directly on the fabricnor puncture it. Small tracked bulldozerswith a maximum ground pressure of 2 psi arecommonly used. The blade is kept high toavoid driving rock down into the fabric.Finally, compaction and grading can be car-ried out with standard compactionequipment. If the installation has sidedrains, these are constructed after the pave-ment.

Earth Retaining WallsAs with road construction, there is no

specific or preferred method for using geotex-tiles for retaining walls. Figure 11-9, page

to the specific needs of the engineer. Thebackfill material can be coarse-grained, fine-grained, or alternating layers of coarse- andfine-g-rained materials.

Construction on SandConstruction on sand, such as a beach or a

desert, presents a severe trafficability prob-lem. The construction of an expedient roadthrough this soil can be expedited by using aplastic geocell material called “sand grid”.This material is in the Army’s inventorystockage (National Stock Number (NSN)5680-01-198-7955). The sand grid is ahoneycomb-shaped geotextile measuring 20feet long, 8 feet wide, and 8 inches deep when

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fully expanded (see Figure 11-10, page11-14).

Sand grids are very useful when developinga beachhead for logistics-over-the-shore(LOTS) operations. Construction of sand-gridroadways proceeds rapidly. A squad-sizedelement augmented with a scoop loader, lightbulldozers, and compaction equipment are allthat is required to construct a sand-grid road.

Procechures. Use the following constructionprocedures for a sand-grid road:

Lay out the road. Establish a center-line that follows the course of theproposed road.Perform the earthwork necessary tolevel the roadway.

Distribute folded sand grids along theroadway.Expand the sand-grid sections andsecure them in place. Use shovels tofill the end cells and some of the sidecells with sand.Use a scoop loader to fill the grids.They should be overfilled to allow fordensification when compacted.Compact the sand, using compactionequipment.Use a scoop loader to back drag ex-cess sand to the road shoulder area ifasphalt or gravel surfacing is used.If available, apply an asphalt surfacetreatment over the filled sand grids toenhance their service life.

Sand grids perform well under wheeled-vehicle traffic. Tracked-vehicle traffic is verydestructive to the sand-grid road. Asphaltsurface treatments reduce sand-grid damagewhen a limited number of tracked vehiclesmust use the road.

Maintenance. Sand-grid roads are easilymaintained. Entire damaged sections can be re-moved or the damaged portion can be cut andremoved and a new grid fitted in its place.

Sand grids have many uses in the theater ofoperations other than just roads. They canalso be used to construct bunkers, revet-ments, retaining walls, and a host of otherexpedient structures.

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CHAPTER 12

S p e c i a l S o i l P r o b l e m s

Misunderstanding soils and their proper-ties can lead to construction errors that arecostly in effort and material. The suitabilityof a soil for a particular use should be deter-mined based on its engineering characteris-tics and not on visual inspection or apparentsimilarity to other soils. The considerationspresented in the following paragraphs willhelp reduce the chances of selecting thewrong soil.

AGGREGATE BEHAVIORGravel, broken stone, and crushed rock are

commonly used to provide a stable layer, suchas for a road base. These aggregate materialshave large particles that are not separated orlubricated by moisture; thus, there is not asevere loss of strength with the addition ofwater. They remain stable even in thepresence of rain or pending within the layer.As a result, these soils can be compacted un-derwater, such as in the construction of ariver ford.

SOIL-AGGREGATE MIXTURESConstruction problems can arise with cer-

tain mixtures of soil and aggregate. Theseinclude dirty gravel, pit-run broken stonefrom talus slopes, clays used in fills, andothers. If there are enough coarse particlespresent to retain grain-to-grain contact in asoil-aggregate mixture, the fine material be-tween these coarse particles often has only aminor effect. Strength often remains higheven in the presence of water. On the otherhand, mixtures of soil and aggregate in whichthe coarse particles are not continuously

in on tact with one another will lose strengthwith the addition of water as though no ag-gregate particles were present. Highplasticity clays (PI > 15)in sand and gravelfills can expand on wetting to reduce grain-to-grain contact, so that strength is reduced anddifferential movement is increased. Thechange in texture from stable to unstable soil-aggregate mixtures can be rather subtle,often occurring between two locations in asingle borrow pit. To assure a stablematerial, usually the mixture should cont-ain no more than about 12 to 15 percent byweight of particles passing a Number 200sieve; the finer fraction should ideallyshow low plasticity (PI < 5).

LATEITES AND LATERITIC SOILSLaterites and lateritic soils form a group

comprising a wide variety of red, brown, andyellow, fine-g-rained residual soils of light tex-ture as well as nodular gravels and cementedsoils. They may vary from a loose material toa massive rock. They are characterized bythe presence of iron and aluminum oxides orhydroxides, particularly those of iron, whichgive the colors to the soils. For engineeringpurposes, the term “laterite” is confined to thecoarse-grained vermicular concrete material,including massive laterite. The term“lateritic soils” refers to materials with lowerconcentrations of oxides.

Laterization is the removal of siliconethrough hydrolysis and oxidation that resultsin the formation of laterites and lateritic soils.The degree of laterization is estimated by the

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silica-sesquioxide (S-S) ratio (SiO2/(Fe2O3 +Al2O3)). Soils are classed by the S-S ratios.The conclusion is—

An S-S ratio of 1.33 = laterite.An S-S ratio of 1.33 to 20 = lateriticsoil.An S-S ratio of 20 = nonlateritic,tropical soil.

LateritesMost laterites are encountered in an al-

ready hardened state. In some areas of theworld, natural laterite deposits that have notbeen exposed to drying are soft with a clayeytexture and mottled coloring, which may in-clude red, yellow, brown, purple, and white.When the laterite is exposed to air or dried outby lowering the ground water table, irre-versible hardening often occurs, producing amaterial suitable for use as a building or roadstone.

Frequently, laterite is gravel-sized, rang-ing from pea-sized gravel to 3 inches minus,although larger cemented masses are pos-sible. A specific form of laterite rock, knownas plinthite, is noteworthy for its potentialuse as a brick. In place, plinthite is softenough to cut with a metal tool, but it hardensirreversibly when removed from the groundand dried.

Lateritic SoilsThe lateritic soils behave more like fine-

grained sands, gravels, and soft rocks. Thelaterite typically has a porous or vesicular ap-pearance. Some particles of laterite tend tocrush easily under impact, disintegratinginto a soil material that may be plastic.Lateritic soils maybe self-hardening whenexposed to drying; or if they are not self-hardening, they may contain appreciableamounts of hardened laterite rock or lateritegravel.

LocationLaterites and lateritic materials occur fre-

quently throughout the tropics andsubtropics. They tend to occur on level orgently sloping terrain that is subject to very

little mechanical erosion. Laterite country isusually infertile. However, lateritic soils maydevelop on slopes in undulating topography(from residual soils), on alluvial soils thathave been uplifted.

ProfilesThere are many variations of laterites and

lateritic profiles, depending on factors such asthe—

Mode of soil formation.Cycles of weathering and erosion.Geologic history.Climate.

Engineering ClassificationThe usual methods of soil classification, in-

volving grain-size distribution and Atterberglimits, should be performed on laterites orsuspected laterites that are anticipated foruse as fill, base-course, or surface-coursematerials. Consideration should be given tothe previously stated fact that some particlesof laterite crush easily; therefore, the resultsobtained depend on such factors as the—

Treatment of the sample.Amount of breakdown.Method of preparing the minus Num-ber 40 sieve material.

The more the soil’s structure is handled anddisturbed, the finer the aggregates become ingrading and the higher the Atterberg limit.While recognizing the disadvantage of thesetests, it is still interesting to note the largespread and range of results for both lateritesand lateritic soils.

Compacted Soil CharacteristicsParticularly with some laterites, break-

down of the coarser particles will occur underlaboratory test conditions. This breakdown isnot necessarily similar to that occurringunder conditions of field rolling; therefore,the prediction of density, shear, and CBRcharacteristics for remolded laboratoryspecimens is not reliable. Strength underfield conditions tends to be much higher thanis indicated by the laboratory tests, providedthe material is not given excessive rolling.Field tests would be justified for supplying

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data necessary for pavement design. Thelaboratory CBR results for laterite showhigher values after soaking than initiallyfound after compaction, indicating a tendencyfor recementation. For lateritic soils, thepresence of cementation in the grain struc-ture also gives the same effect. In addition,the field strengths may be higher than thosein the laboratory, although in a much lesspronounced fashion. If the soil is handledwith a minimum of disturbance and remold-ing, laboratory tests do furnish a usable basisfor design; however, lesser disturbance andhigher strengths may be achieved under fieldconditions.

Pavement ConstructionThe laterized soils work well in pavement

construction in the uses described in the fol-lowing paragraphs, particularly when theirspecial characteristics are carefully recog-nized. While the AASHTO and the Corps ofEngineers classification systems andspecifications are the basis for lateritematerial specification, experience by high-way agencies in countries where laterites arefound indicates that excellent performancefrom lateritic soils can be achieved by modify-ing the temperate zone specifications. Themodified specifications are less exacting thaneither the AASHTO or the Corps of Engineersspecifications, but they have proven satisfac-tory under tropical conditions.

Subgrade. The laterites, because of theirstructural strength, can be very suitable sub-grades. Care should be taken to providedrainage and also to avoid particle break-

down from overcompaction. Subsurface in-vestigation should be made with holes atrelatively close spacing, since the depositstend to be erratic in location and thickness.In the case of the lateritic soils, subgrade com-paction is important because the leachingaction associated with their formation tendsto leave behind a loose structure. Drainagecharacteristics, however, are reduced whenthese soils are disturbed.

Base Course. The harder types of lateriteshould make good base courses, Some areeven suitable for good quality airfield pave-ments. The softer laterites and the betterlateritic soils should serve adequately for sub-base layers. Although laterites are resistantto the effects of moisture, there is a need forgood drainage to prevent softening andbreakdown of the structure under repeatedloadings. Base-course specifications forlateritic soils are based on the following soiluse classifications:

Class I (CBR 100).Class II (CBR 70 to 100).Class III (CBR 50 to 70).

Gradation requirements for laterite andlaterite gravel soils used for base courses andsubbases are listed in Table 12-1. Atterberglimits and other test criteria for laterite basecourse materials are listed in Table 12-2, page12-4.

Subbase. Subbase criteria are listed inTable 12-1, and Table 12-3, page 12-4. Thesecriteria are less stringent than those found inTW 5-330, which limits subbase soil materials

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to a maximum of 15 percent fines, a LL of 25,and a PI of 5.

Surfacing. Laterite can provide a suitablelow-grade wearing course when it can be com-pacted to give a dense, mechanically stablematerial; however, it tends to corrugateunder road traffic and becomes dusty duringdry weather. In wet weather, it scours andtends to clog the drainage system. To preventcorrugating, which is associated with loss offines, a surface dressing maybe used. Alter-natively, as a temporary expedient, regularbrushing helps. The lateritic soils, beingweaker than the laterites, are not suitable fora wearing course. Their use for surfacingwould be restricted to—

Emergencies.Use under landing mats.Other limited purposes.

Stabilization. The laterite and lateriticsoils can be effectively stabilized to improvetheir properties for particular uses. How-ever, because of the wide range in lateritic soilcharacteristics, no one stabilizing agent hasbeen found successful for all lateriticmaterials. Laboratory studies, or preferably

field tests, must be performed to determinewhich stabilizing agent, in what quantity,performs adequately on a particular soil.Some that have been used successfully are—

Cement.Asphalt.Lime.Mechanical stabilization.

Laterite and lateritic soils can still performsatisfactorily in a low-cost, unsurfaced road,even though the percent of fines is higherthan is usual in the continental UnitedStates. This is believed to be due to thecementing action of the iron oxide content.Cement and asphalt work best with materialof a lower fines content. When fines are quiteplastic, adding lime reduces the plasticity toproduce a stable material. Field trials makeit possible to determine the most suitablecompaction method, which gives sufficientdensity without destroying the granule struc-ture and cementation. Generally, vibratorycompaction is best. Laboratory test programsfor tropical conditions do not ordinarily in-clude freeze-thaw tests but should check theinfluence of wetting and drying. The finer-grained lateritic soils may contain enough

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active clay to swell and shrink, thus tendingto destroy both the natural cementation andthe effect of stabilization.

SlopesThe stiff natural structure of the laterites

allows very steep or vertical cuts in the hardervarieties, perhaps to depths of 15 to 20 feet.The softer laterites and the lateritic soilsshould be excavated on flatter than verticalslopes but appreciably steeper than would beindicated by the frictional characteristics ofthe remolded material. It is important toprevent access of water at the top of the slope.

CORAL“Coral” is a broad term applied to a wide

variety of construction materials derivedfrom the accumulation of skeletal residues ofcoral like marine plants and animals. It isfound in various forms depending on the de-gree of exposure and weathering and mayvary from a hard limestone like rock to acoarse sand. Coral develops in tropical oceanwaters primarily in the form of coral reefs, butmany of the South Pacific islands and atollsare comprised of large coral deposits. As ageneral rule, living colonies of coral arebright-colored, ranging from reds throughyellows. Once these organisms die, theyusually become either translucent or assumevarious shades of white, gray, and brown.

TypesThe three principal types of coral used in

military construction are—Pit run coral.Coral rock.Coral sand.

Pit-Run Coral. Pit-run coral usually con-sists of fragmented coral in conjunction withsands and marine shells. At best, it classifiesas a soft rock even in its most cemented form.The CBR values for this material may varybetween 5 and 70. This material seldomshows any cohesive properties. In general,pit-run coral tends to be well graded, but den-sities above 120 pcf are seldom achieved.

Coral Rock. Coral rock is commonly foundin massive formations. The white type is veryhard, while the gray type tends to be soft, brit-tle, and extremely porous. The CBR valuesfor this material vary from 50 to 100. Den-sities above 120 pcf are common except insome of the soft rock.

Coral Sand. Coral sand consists of decom-posed coral rock that may be combined withwashed and sorted beach sands. Generally, itclassifies as a poorly graded sand and seldomwill more than 20 percent of the soil particlespass a Number 200 sieve. The CBR values forthis material vary between 15 and 50. Be-cause of the lack of fines, compaction isdifficult and densities above 120 pcf are un-common.

SourcesCoral may be obtained from—

Construction site cuts.Quarries.Wet or dry borrow pits worked inbenches.

Rooters should be used to loosen the softerdeposits, and the loosened material should bemoved with bulldozers to power shovels forloading into trucks or other transport equip-ment. Rooting and panning are preferable insoft coral pits or shallow lagoons. Wherecoral requires little loosening, draglines andcarryall scrapers can be used. Occasionally,coral from fringing reefs and lagoons can bedug by draglines or shovels, piled as acauseway, and then trucked away progres-sively from the seaward end. Hard coral rockin cuts or aggregate quarries requires consid-erable blasting. In both pit and quarryoperations, hard coral “heads” are often foundembedded in the softer deposits, presenting ahazard to equipment and requiring blasting.

Blasting hard coral rock differs somewhatfrom ordinary rock quarrying since coral for-mations contain innumerable fissures invarying directions and many large voids. Theporosity of the coral structure itself decreasesblasting efficiency. Conventional use of

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low-percent dynamite in tamped holesproduces the most satisfactory results.

Shaped charges are ineffective, especiallywhen used underwater; cratering charges, al-though effective, are uneconomical. Usuallyholes 8 to 12 feet deep on 4- to 8-foot centersare required to get adequate blasting effi-ciency.

UsesCoral may be used as—

Fills, subgrades, and base courses.Surfacing.Concrete aggregate.

Fills, Subgrades, and Base Courses.When properly placed, selected coral that isstripped from lagoon or beach floors or quar-ried from sidehills is excellent for fills,subgrades, and base courses.

Surfacing. White or nearly white coral withproperly proportioned granular sizes com-pacted at OMC creates a concrete like surface.The wearing surface requires considerablecare and heavy maintenance since coralbreaks down and abrades easily under heavytraffic. Conversely, coral surfaces are ex-tremely abrasive, and tire durability isgreatly reduced.

Concrete Aggregate. Hard coral rock, whenproperly graded, is a good aggregate for con-crete. Soft coral rock makes an inferiorconcrete, which is low in strength, difficult toplace, and often of honeycomb structure.

ConstructionConstruction with coral presents some spe-

cial problems, even though the uses arealmost the same as for standard rock and soilmaterials. Since coral is derived from livingorganisms, its engineering characteristicsare unique. Use the steps discussed in the fol-lowing paragraphs to help minimizeconstruction problems:

Whenever coral is quarried from reefsor pits containing living coral

deposits, allow the material to aerateand dry for a period of 6 days, if pos-sible, but not less than 72 hours.Living coral organisms can remainalive in stockpiles for periods of up to72 hours in the presence of water. If“live” coral is used in construction,the material exhibits high swell char-acteristics with accompanying loss ofdensity and strength.Carefully control moisture contentwhen constructing with coral. In-creases of even 1 percent above OMCcan cause reductions of 20 percent ormore in densities achieved in certaintypes of coral. For best results, com-paction should take place between theOMC and 2 percent below the OMC.Maintenance on coral roads is bestperformed when the coral is wet.When added to coral materials, saltwater gives higher densities, with thesame compactive effort, than freshwater. Use salt water in compactionwhenever possible.Hard coral rock should not be used asa wearing surface. This rock tends tobreak with sharp edges when crushedand easily cuts pneumatic tires.When constructing with hard coralrock, use tracked equipment as muchas possible.

DESERT SOILSDeserts are very arid regions of the earth.

Desert terrain varies widely as do the soilsthat compose the desert floor. The desertclimate has a pronounced effect on thedevelopment of desert soils and greatly im-pacts on the engineering properties of thesesoils. Engineering methods effective for roador airfield construction in temperate or tropi-cal regions of the world are often ineffectivewhen applied to desert soils.

Because of wind erosion, desert soils tend tobe of granular material, such as—

Rock.Gravel.Sand.

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Stabilization of the granular material is re-quired to increase the bearing capacity of thesoil. The options available for stabilizingdesert soils are more limited. The primarymeans of stabilizing desert soils are—

Soil blending.Geotextiles.Bituminous stabilization.

Chemical admixtures generally performpoorly under desert conditions because theycease hydration or “set up” too quickiy andtherefore do not gain adequate strength.

If a source of fines is located, the fines maybe blended with the in-place soil, improvingthe engineering characteristics of the resul-tant soil. However, before using the finematerial for blending, perform a complete soilanalysis on the material. Also, consider un-usual climatic conditions that may occurduring the design life of the pavement struc-ture. During Operation Desert Storm, manyroads in Saudi Arabia were stabilized withfine material known as marl. The roads per-formed well until seasonal rains occurred;then they failed.

Geotextiles can be used alone, such as thesand grid, or in combination with bituminoussurfacing. The latter is the most effective.

Bituminous treatment is the most effectivemethod of stabilizing desert soils for tem-porary road and airfield use.

ARCTIC AND SUBARCTIC SOILSConstruction in arctic and subarctic soils in

permafrost areas is more difficult than intemperate regions. The impervious nature ofthe underlying permafrost produces poor soildrainage conditions. Cuts cause changes tothe subsurface thermal regime. Stability anddrainage problems result when cuts aremade. If the soil contains visible ice, or ifwhen a sample of the frozen soil is thawed itbecomes unstable, it is termed thaw-un-stable. Cuts into these types of frozen soilsshould be avoided; however, if this is not pos-sible, substantial and frequent maintenance

will undoubtedly be required. Cuts cangenerally be made into dry frozen (for ex-ample, thaw-stable) soils without majorproblems. Thaw-stable soils are generallysandy or gravelly materials.

Road and runway design over frost-susceptible soils must consider both frosteffects and permafrost conditions. Adjust-ments to the flexible pavement design mayberequired to counter the effects of frost andpermafrost.

Depths of freeze and thaw are usually sig-nificantly altered by construction. Figure12-1, page 12-8, illustrates the effect of clear-ing and stripping on the depth to permafrostafter 5 years. The total depth of thaw isstrongly influenced by the surface materialand its characteristics (see Table 12-4, page12-8).

Increasing the depth of the nonfrost-susceptible base course material can preventsubgrade thawing. The required base thick-ness may be determined from Figure 12-2,page 12-9. The thawing index is determinedlocally by calculating the degree days of thaw-ing that take place. Thawing degree daysdata is usually available from local weatherstations or highway departments. If thawingdegree days data is unavailable, they can beestimated from information contained inFigures 12-3 through 12-5, pages 12-10through 12-12.

Surface-Thawing IndexThe surface-thawing index may be com-

puted by multiplying the thawing indexbased on air temperature by a correction fac-tor for the type of surface. For bituminoussurfaces, multiply by a factor of 1.65; for con-crete, multiply by a factor of 1.5.

For example, design a road over a per-mafrost region to preclude thawing of thepermafrost. The mean air thawing index is1,500 degree days (Fahrenheit). Base coursematerial moisture content is 7 percent.Bituminous surface is to be used.

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If the subgrade is thaw-unstable, a granular1,200 degree days (Fahrenheit) x 1.6 = 1,920surface-thawing index (air-thawing index) xbituminous correction factor)

What is the thickness of the base coursematerial required to prevent thawing of thepermafrost? (See Figure 12-2).

150 inches of the base at 5 percent moisture;adjust for moisture difference

150 x 0,87 = 130.5 inches

Therefore, for this example, permafrost thaw-ing can be prevented by constructing a130.5-inch base-course layer.

If the subgrade is thaw-stable, a soil thatdoes not exhibit loss of strength or settlementwhen thawed may accept some subgradethawing because little settlement is expected.

embankment 4 to 5 feet thick is generally ade-quate to carry all but the heaviest traffic.Considerable and frequent regrading is re-quired to maintain a relatively smoothsurface. Embankments only 2 to 3 feet thickhave been used over geotextile layers thatprevent the underlying fine-grained sub-grade from contaminating the granular fill.Additional fill may be necessary as thawingand settlement progress. It is usuallydesirable to leave the surface organic layer in-tact. If small trees and brush cover the site,they should be cut and placed beneath theembankment. They serve as a barrier toprevent mixing of the subgrade with theembankment material. Figure 12-6, page12-13, and Figure 12-7, page 12-14, assist theflexible pavement designer in determiningthe depth of thaw and freeze, respectively,

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Special Soil Problems 12-11

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beneath pavements with gravel bases. Thecurves are based on the moisture content ofthe subgrade soil.

Ecological Impact of ConstructionThe arctic and subarctic ecosystems are

fragile; therefore, considerable thought mustbe given to the impact that constructionactivities will have on them, Figure12-8, page 12-15, shows the long-term (26 years)ecological impacts of construction activities inFairbanks, Alaska. Stripping, compacting,or otherwise changing the existing groundcover alters the thermal balance of the soil.

Unlike temperate ecosystems that canrecover from most construction activities in arelatively short period of time, the arctic andsubarctic ecosystems do not recover quickly.In fact, once disturbed, the arctic and sub-arctic ecosystems can continue to undergodegradation for decades following the distur-bance.

The project engineer must consider theselong-term environmental impacts, from theperspective of a steward of the environment,and the effects such environmental degrada-tion may have on the structure’s useful life.

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Special Soil Problems 12-14

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Special Soil Problems 12-15

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APPENDIX A

California Bearing Ratio

Design Methodology

The CBR is the basis for determining thethickness of soil and aggregate layers used inthe design of roads and airfields in the theaterof operations. A soil’s CBR value is an indexof its resistance to shearing under a standardload compared to the shearing resistance of astandard material (crushed limestone) sub-jected to the same load.

CBR DESIGN METHODOLOGYThe CBR design methodology has four

major parts:Evaluate the soil to determine its en-gineering characteristics (gradation,Atterberg limits, swell potential,Proctor test (CE 55 compaction test)and CBR test). These tests are per-formed by a Materials QualitySpecialist, Military OccupationalSpeciality (MOS) 51G or a soils test-ing laboratory according to standardtesting procedures (see TM 5-530).Evaluate the laboratory data to deter-mine the initial design CBR valueand the compactive effort to be ap-plied during construction.Evaluate all soil data to determinethe final design CBR and construc-tion use of the soil or aggregate.Determine the thickness of the soillayer based on the final design CBRand the road or airfield use category(see TM 5-330).

This appendix focuses on the second and thirdparts of the methodology.

CBR Design FlowchartThe CBR Design Flowchart (see Figure A-1,

pages A-2 and A-3) is a useful tool when deter-mining the initial and final design CBRvalues.

Step 1 - Look at the Compaction Curves.For CBR analysis, soils are classified into oneof three soil groups:

Free-draining.Swelling.Nonswelling.

The compaction curve on page 1 of a Depart-ment of Defense (DD) Form 2463 gives anindication as to the group in which a par-ticular soil falls. A U-shaped compactioncurve indicates a free-draining soil. A bell-shaped compaction curve indicates that thesoil is either a swelling or a nonswelling soil.

Step 2- Look at the Swell Curve. To distin-guish between a swelling and nonswellingsoil, look at the swell data plotted on a DDForm 1211. If the percent of swell exceeds 3percent for any soil moisture content, the soilis classified as a swelling soil. If the percent ofswell never exceeds 3 percent, the soil is non-swelling.

Step 3- Find the Peak of the CE 55 Curve.The maximum dry density is found at the

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California Bearing Ratio Design Methodology A-2

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peak of the CE 55 curve. For free-drainingsoils, the peak of the curve occurs at the pointof the curve where there is no increase in drydensity with an increase in moisture.

Step 4- Determine the Design MoistureRange. The design moisture range is in-fluenced by the soil group.

Free-draining soils. The moisturecontent that corresponds to the maxi-mum dry density is the MMC. Thedesign moisture range is MMC + 4percent. For example, if the maxi-mum dry density occurred at 13 per-cent soil moisture, the MMC wouldequal 13 percent and the design mois-ture range would be 13 to 17 percentsoil moisture.Swelling soils. Army standards per-mit no more than 3 percent swell tooccur after a soil has been placed andcompacted. Therefore, swelling soilsmust be preswelled to a moisture con-tent that will result in 3 percent orless swell. The moisture content atwhich 3 percent swell occurs is calledthe MMC. The design moisture rangefor a swelling soil is MMC + 4 per-cent. The moisture content cor-responding to the maximum drydensity is not considered for swellingsoils.Nonswelling soils. The moisture con-tent that corresponds to the maxi-mum dry density is the OMC. Thedesign moisture range is OMC ±2percent. For example, if the OMC is12 percent, the design moisture rangewould be 10 to 14 percent.

PI

P I 20. cohesion-

values

Step 5 - Find the Soil Plasticity Index.This step applies to nonswelling soils only.Noncohesive soils (PI to greater densities than cohesive soils (PI5). If the soil is cohesionless, look at the CBRFamily of Curves on page 3 of a DD Form 2463to determine the cornpactive effort.

5)can be compacted

Step 6 - Determine the Density Range.The theater-of-operations, standard compac-tion range is 5 percent, unless otherwise

stated. The maximum dry density is thebasis for determining the density range (com-pactive effort).

Free-draining soils. They are comp-acted to between 100 percent and105 percent maximum dry density.Swelling soils. They are compacted tobetween 90 and 95 percent of maxi-mum dry density.NonsweIling soils.—

—

—

PI > 5. Cohesive nonswelling soilsare compacted to between 90% and95% of maximum dry density.

5 and CBR < 20. cohesionless,nonswelling soils having CBRvalues below 20 are compacted tobetween 95 percent and 100 per-cent maximum dry density.

5 and CBRless, nonswelling soils having CBR

20 are compacted to be-tween 100 percent and 105 percentmaximum dry density.

Step 7 - Plot the Density Range. Draw ver-tical lines on the CBR Family of Curves onpage of a DD 2463, corresponding to the den-sity range determined in previous steps.Circle the moisture values that correspond tothe moisture range determined in earlier (fivemoisture values should be circled).

Step 8- Determine the Initial DesignCBR. Using the CBR Family of Curves, findwhere each moisture curve, within the mois-ture range, enters and exits the density-rangelimit lines drawn in previous step. Find theCBR value corresponding to the lowestentrance or exit point of each curve. This isthe initial design CBR.

Step 9- Gather the Soil Data. The CBR isnot the only criteria used when determiningwhere to place a soil in the road or airfielddesign. Criteria for the LL, the PI, and thegrain-size distribution must also be satisfied.Subbase and select material criteria arefound in Table A- 1. Base-course gradation re-quirements are found in Table A-2.

Step 10 - Determine the Final DesignCBR. Using the initial design CBR value,

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determine if the soil material is suitable foruse as a base, subbase, select, or subgradelayer material. Next, look at the gradationrequirements for use in that layer. Finally,look at the LL and the PI criteria. If a soilmaterial meets all the criteria for use in a soillayer, then it can be placed in that layer. If itfails to meet all criteria for its intended use,consider using the material in another layer.The final design CBR is determined by thecriteria that the soil material meets. The fol-lowing examples illustrate this point:

A soil material has an initial designCBR value of 65. Based on CBRvalue, this material is suitable for usein a base-course layer for a road. Themaximum aggregate size is 1.5inches. When evaluating the soilagainst the base-course criteria inTable A-2, page A-5, we find that thepercent passing the Number 40 sieveis 6 percent, which is less than theminimum al1owable for use as a basecourse. Therefore, we cannot use thematerial as a base course, butperhaps it can be used as a subbase.By evaluating the soil against theCBR 50 subbase criteria (see TableA-1, page A-5), we find that the soilmaterial meets all criteria. The finaldesign CBR for this soil would beCBR 50. It would be used as a CBR50 subbase.A soil material has an initial designCBR of 37. We are considering theuse of this material as a subbase.There are no criteria for a CBR 37subbase; therefore, we will use thefollowing rule:– If a soil material meets the criteria

of the next higher subbase, thefinal design CBR will be the sameas the initial design CBR.

- If a soil material fails to meet thecriteria of the next higher subbasebut meets the criteria of a lowersubbase or select material, the ini-tial design CBR will be adjusteddownward to the maximum CBRvalue of the layer at which allcriteria were met, which becomesthe final design CBR.

California Bearing Ratio Design Methodology A-6

In our example, if the soil material met theCBR 40 subbase criteria, the final designCBR would be 37 and the road or airfieldwould be designed with a CBR 37 subbaselayer. If the soil failed to meet the CBR 40subbase criteria but did meet the CBR 30 sub-base criteria, the final design CBR would be30 and the road or airfield would be designedwith a CBR 30 subbase. If the soil failed tomeet both the CBR 40 and CBR 30 subbasecriteria, the material would be evaluatedagainst the select material criteria. If it metthe select criteria, the final design CBR wouldbe 20.

CBR DESIGN PRACTICAL EXERCISEIn preparation for an airfield construction

project in support of a Marine Corps exercise,a soil sample was obtained from Rio MetaPlain, Venezuela. The soil was tested, andthe test results are presented in Figures A-2through A-9, pages A-7 through A-1 4. Usingthe USCS, the soil was classified as a (GM-GC) (see Figure A-2, and Figure A-3, pageA-8).

What are the initial and final design CBRsof this soil? Where will this soil be placed inthe airfield design?

Looking at the density-moisture curve onFigure A-4, page A-9, we see that the compac-tion curve is bell-shaped (Step 1); therefore,the soil is either swelling or nonswelling. Theswell data is shown in Figure A-5, page A-10.Swelling never exceeds 3 percent at any pointon the curve (Step 2). The soil is nonswelling.

Maximum dry density occurs at 125 pcf(Figure A-2, page A-7), and the OMC is 11.3percent. The design moisture range is 9.3 to13.3 percent (Steps 3 and 4).

The LL and PL were determined to be 23and 18, respectively. PI= LL - PL (23 -18= 5);therefore, the soil is cohesionless. We mustlook at the CBR Family of Curves to deter-mine the compactive effort (Step 5).

Figure A-6, page A-11, shows the CBRFamily of Curves. Note that while somevalues exceed 20, most of the data points areclustered below 20. Thus, we will compact

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this soil to a density between 95 percent and100 percent maximum dry density or between118.75 and 125 pcf (Step 6). When plotted onthe density-moisture curve with the moisturerange (9.3 to 13.3 percent), the specificationblock is formed (see Figure A-7, page A-12).

The CBR Family of Curves, Figure A-8,page A-13, shows the density range superim-posed on the curves and the moisture rangevalues circled (in this case we’ve circled themoisture values 9-13) (Step 7). Followingeach moisture curve in our range and mark-ing where it enters and exits the densitylimits, we find that the lowest CBR value oc-curs at the point where the 13 percentmoisture curve exits the 118.75 pcf densitylimit line. Interpolating between the 13 per-cent and 14 percent moisture curves, 13.3percent moisture results in an assured CBR val-ue of 7.5 (see Figure A-9, page A-14) (Step 8).

The initial design CBR of this soil is 7.5.Because of the low CBR, we can consider thissoil material for use as select material if itmeets the criteria of Table A-1, page A-.5.Looking at DD Form 1207 (Figure A-7, page

A-12), we first check the maximum aggregatesize and see that it is 2 inches. The maxi-mum allowable aggregate size (see Table A-1page A-5, for a select material used in the con-struction of an airfield is 3 inches; therefore,our soil meets this criteria. Next, we check forthe percent passing the Number 200 sieveand find that the percent passing the Number200 sieve is 23 percent. From Table A-1, pageA- 5, we find that the select criteria allows upto 25 percent of the material to pass the No200 sieve; therefore, our soil meets thiscriteria. Finally, we must evaluate the LLand PI of our soil against the select criteria inTable A-l, page A-5. When we do this, we findthat our soil’s PI of 23 and LL of 5 meet the re-quirements.

The final design CBR of the soil is 7.5, andit is suitable for use as a select material.

The final portion of the CBR design processis to determine the thickness of the road orairfield structure based on the CBR values ofthe subgrade, select, subbase, and base-course materials available for use in the con-struction effort. This is discussed in detail inTM 5-330.

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California Bearing Ratio Design Methodology A-10

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California Bearing Ratio Design Methodology A-11

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APPENDIX B

A v a i l a b i l i t y o f F l y A s h

Fly ash is a pozzolanic material that is a by-product of coal-fired, electrical power-generation plants. Because of its pozzolanicproperties, it can be used as a—

Soil stabilizer.Liming material.Cement component.

Depending on its calcium oxide (CaO) con-tent, fly ash may be used as a stand-aloneproduct or in combination with other poz-zolanic materials.

Fly ash is divided into two classes, based ontheir CaO content. They are—

Class F.Class C.

Class F fly ash has a low CaO content (lessthan 10 percent) and is not suitable for use asa stand-alone product for engineering pur-poses. Class C fly ash is often referred to as“high lime” fly ash. Its CaO content must bea minimum of 12 percent and frequently ex-ceeds 25 percent. Class F fly ash originatesfrom hard coal (anthracite and bituminouscoal), whereas Class C fly ash originates frombrown coal (lignite and subbituminous coal).

Fly ash occurs throughout the world. Inmany countries, both classes of fly ash can befound. The likelihood of finding a particularclass of fly ash depends on the individualcountry. Hard coal is more frequently used inindustrialized countries in the manufactureof steel. Therefore, in industrialized nationshaving both hard and brown coal reserves,

the amount of brown coals used for powergeneration is likely to be greater; thus thepercentage of Class C fly ash would begreater.

The major coal-producing countries and thepercentages of the hard and brown coal reser-ves are found in Table B-1.

Availability of Fly Ash B-1

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APPENDIX C

H a z a r d s o f C h e m i c a l

S t a b i l i z e r s

The major hazards associated with chemi-cal stabilizers and the precautions to takewhen using them are identified in this appen-dix. When receiving chemical stabilizers, youshould also receive a Material Safety DataSheet (MSDS) that is prepared by themanufacturer to give you more detailed infor-mation on the product. Generally, the hazardof airborne particles is reduced significantlyin the open air on the construction site. Inthis appendix, ventilation is discussed whenmaterials are handled in enclosed areas, suchas soils laboratories. Due to differences inmanufacturers, the MSDS may list hazardsthat are slightly different from the onesb e l o w .

PORTLAND CEMENTHealth-Hazard Data

Signs and symptoms of overexposure.Alkali burns.Irritation to the eyes and the res-piratory system.Allergic dermatitis.

Emergency and first-aid procedures.Irrigate the eyes with water.Wash the affected areas of the bodywith soap and water.

Precautions for Safe Handling and UseProcedures for cleanup of released or

spilled material.

Use dry cleanup methods that do notdisperse the dust into the air.Avoid breathing the dust.

Control MeasuresRespiratory protection. Use a

stitute of Occupational Safety(NIOSH)-approved respirator.

Eye protection. Use goggles.

HYDRATED LIMEReactivity Data

Avoid acids and fluorine.

National In-and Health

Health-Hazard DataRoutes of entry.

Eyes.Skin.Inhalation.Ingestion.

Acute reactions.Irritation of the eyes.Irritation of the skin.Irritation of the respiratory tract.Irritation and inflammation of the di-gestive system.

Chronic reactions.Corrosion of the eyes.Corrosion of the skin.

Hazards of Chemical Stabilizers C-1

FM 5-410

Irritation of the respiratory tract.Irritation and inflammation of thedigestive system.

Signs and symptoms of overexposure.Irritation of the skin and eyes.Irritation of the respiratory tract.Irritation of the digestive system.

Medical conditions aggravated by ex-posure.

Respiratory disease.Skin conditions.

Emergency and first-aid procedures.If the material gets into the eyes,flush them thoroughly with largeamounts of water while holding theeyelids apart.If the material gets on the skin, washthoroughly with soap and water.If the material is inhaled, get medicalattention.If the material is ingested, do not in-duce vomiting. Get medical atten-tion.

Precautions for Safe Handling and UseProcedures for the cleanup of spilled or

released materials.Wipe the material up and place it in adisposal container (some manufac-turers recommend using a vacuumcleaning system).Remove the residue with water.

Procedure for the disposal of wastematerial. Dispose of the waste according tolocal, state, and federal regulations.

Procedure for the handling and storage ofmaterial. Store the material in tightly sealedcontainers away from incompatiblematerials.

Control MeasuresRespiratory protection. Use a dust-filter

mask.

Ventilation. Ensure that the generalmechanical ventilation meets the ThresholdLimit Value (TLV) and Permissible ExposureLimit (PEL).

Protective gloves. Use leather or rubbergloves.

Eye protection. Use well-fitted goggles.

Other protective equipment. Wear longsleeves and pants.

Work hygiene. Use good hygiene practices;avoid unnecessary contact with this product.

Supplemental safety and health data. Userespiratory protection if exposure limits can-not be maintained below the TLV and PEL.

QUICKLIMEFire- and Explosion-Hazard Data

Extinguishing media. Use a dry chemical(CO2) (water will cause evolution of heat).

Special fire-fighting procedures. Do notuse water on adjacent fires.

Unusual fire and explosion hazards. Thematerial may burn but does not ignite readily.Some materials may ignite combustibles(wood, paper, and oil).

Reactivity DataConditions to avoid. Moisture.

Material to avoid. Acids and oxidizingmaterials.

Health-Hazard DataRoutes of entry.

Eyes.Skin.Inhalation.Ingestion.

Signs and symptoms of overexposure.Conjunctivitis.

Hazards of Chemical Stabilizers C-2

FM 5-410

Corneal ulceration.Iritis.Skin inflammation.Skin ulceration.Lung inflammation.

Emergency and first-aid procedures.Keep unnecessary people away.Stay upwind.Keep out of low areas.Isolate the hazard and deny entry.Wear a self-contained breathing ap-paratus and full protective clothing.Avoid contact with solid materials.Irrigate the eyes with water.Wash the contaminated areas of thebody with soap and water.Do not induce vomiting if thematerial is swallowed. If the victim isconscious, have him drink milk orwater.

Precautions for Safe Handling and UseProcedures for the cleanup of released or

spilled material.Sweep the material into a largebucket.Dilute it with water and neutralize itwith 6M-HC1.Drain into an approved storage con-tainer with sufficient water.

Procedures for the disposal of wastematerial.

Put the material into a large vesselcontaining water. Neutralize withHC1.Discharge into an approved disposalarea with sufficient water.Do not allow calcium oxide (CaO) toenter water intakes; very low con-centrations of it are harmful toaquatic life.

Procedures for the handling and storage ofmaterial.

Protect containers fromdamage.Store in a cool, dry place.

physical

Separate from other storage itemsand protect from acids and oxidizingmaterials.

Precautions to take for personal safety. Wear chemical goggles. Wear a mechanical filter respirator. Wear rubber protective clothing.

Control MeasuresRespiratory protection. Use a self-

contained breathing apparatus.

Ventilation. Requires a local exhaust vent.

Protective gloves. Use rubber gloves.

Eye protection. Use chemical goggles.

Other protective equipment. Wear rubberprotective clothing.

FLY ASHHealth-Hazard Data

Lethal dose (LD) 50- Lethal concentration(LC) 50 mixture. TLV 10 milligrams/cumula-tive

Routes of entry.Skin.Inhalation.

Acute reaction.ritation.

Can cause minor skin ir-

Chronic reaction. May cause pulmonarydisease if exposed to an excessive concentra-tion of dust for a long period of time.

Signs and symptoms of overexposure.Development of pul-monary disease.Irritation of the skin.

Precautions for Safe Handling and UseProcedures for the cleanup of released or

spilled material.Vacuum or sweep up the spill.Use a dust suppressant agent ifsweeping is necessary.

Hazards of Chemical Stabilizers C-3

FM 5-410

Wet down large spills and scoop themup.

Procedure for the disposal of wastematerial. Dump the material in landfills ac-cording to local, state, and federalregulations.

Procedures for the handling and storage ofmaterial.

Avoid creating dust.Maintain good housekeeping prac-tices.

Control MeasuresRespiratory protection. Use an NIOSH-ap-

proved respiratory for protection againstpneumoconiosis-producing dusts.

Ventilation. Provide local exhaust ventila-tion to keep below the TLV.

ASPHALT CEMENTFire- and Explosion-Hazard Data

Flash point. 100 degrees Fahrenheit.

Extinguishing media.CO2.Foam.Dry chemicals.

Special fire-fighting procedures. Wear anNIOSH-approved respirator/full protectivegear.

Unusual fire and explosion hazards.Vapors may ignite explosively.

Reactivity DataConditions to avoid. Heat and flames.

Hazardous decomposition products.CO.CO2.Hydrocarbons.

Health-Hazard DataSigns and symptoms of overexposure. May

become dizzy, lightheaded, or have a

headache. If this occurs, remove the victimfrom exposure and provide him with ade-quate ventilation.

Emergency and first-aid procedures.Avoid contact with the skin.Do not ingest. If swallowed, do notinduce vomiting. Get medical atten-tion.

Precautions for Safe Handling and UseProcedures for the cleanup of released or

spilled material. Scrape the material intocontainers and dispose of it according to local,state, and federal regulations.

Procedures for the handling and storage ofmaterial.

Store below 140 degrees Fahrenheit.Do not store near heat or flame.

Control MeasuresRespiratory protection. None is required

if ventilation is adequate.

Ventilation. Recommend a local exhaustvent.

Eye protection. Use normal precautions.

Other protective measures. Wash thehands and other areas of contact after use.

CUTBACK ASPHALTFire- and Explosion-Hazard Data

Flash point. 65 degrees Fahrenheit.

Extinguishing media.CO2.Dry chemicals.Halogenated agents.Foam.Steam or water fog.

Health-Hazard DataSign of overexposure. Thermal burns to

the eyes and skin from the heated material.

Emergency and first-aid procedures.

Hazards of Chemical Stabilizers C-4

FM 5-410

Flush the eyes with cool water for atleast 15 minutes.Wash the affected areas of the bodywith soap and water.Remove the victim to an uncontam-inated area if adverse effects occurfrom inhalation. Giveration if the victim isGet medical attention. Induce vomiting if awas swallowed. Gettion.

artificial respi-not breathing.

large amountmedical atten-

Precautions for Safe Handling and UseProcedures for the cleanup of released or

spilled material.Contain and remove the material bymechanical means.Keep the material on an absorbentmaterial.Keep the material out of sewers andwaterways.

Procedure for the disposal of waste. Dis-pose of the material according to local, state,and federal regulations.

Procedure for the handling and storage ofmaterial. Keep the container closed.

Control MeasuresRespiratory protection. Use an NIOSH-ap-

proved respirator for organic vapors if it isabove the TLV.

Ventilation. Provide local exhaust ventila-tion to keep it below the TLV.

Protective gloves. Wear rubber gloves.

Eye protection. Use safety glasses or gog-gles.

Other protective equipment. Wear workclothes and gloves if prolonged or repeatedcontact is likely.

Hazards of Chemical Stabilizers C-5

FM 5-410

G l o s s a r y

greater than or equal to

less than or equal to

unit weight

wet unit weight

dry unit weight

A horizon The upper layer of a typical soil. It contains a zone of accumulation of organicmaterials in its upper portion and a lower portion of lighter color from which soil colloidsand other soluble constituents have been removed.

AASHTO American Association of State Highway and Transportation Officials

abrasion Occurs when hard particles are blown against a rock face causing the rocks tobreak down. As they are broken off, the resulting fragments are carriedaway by wind. Abrasion also occurs due to water and glacial action.

acid test Used to determine the presence of carbonates and is performed by placing a fewdrops of hydrochloric acid on the surface of a rock.

adobe Calcareous silts and sandy-silty clays, usually high in colloidal clay content, foundin the semiarid regions of the southwestern United States and NorthAfrica.

adsorbed water Thin films of water that adhere to the separate oil particles.

AFM Air Force manual

AFP Air Force publication

agronomic dust control This method consists of establishing, promoting, or preservingvegetative cover to prevent or reduce dust generation from exposed soilsurfaces.

AI Airfield Index

airfield cone penetrometer Used by engineering personnel to determine an index of soilstrengths (airfield index) for various military applications. It serves as anaid in maintaining field control during construction operations.

airfield index An index used to describe subgrade soil strength, based on data from theairfield cone penetrometer.

alluvial fan A dry-land counterpart of deltas.

Glossary-1

F M 5 - 4 1 0

alluvium Deposits of mud, silt, and other material commonly found on the flatlands alongthe lower courses of streams.

Alpine glaciation Takes place in mountainous areas and generally results in the creationof mainly erosional forms. Features are very distinctive and easy torecognize such as a U-shaped profile in contrast to the V-shaped profileproduced by fluvial erosion.

amphiboles Hard, dense, glassy to silky minerals found chiefly in intermediate to dark ig-neous rocks and gneisses and schists. They generally occur as short to longprismatic crystals with a nearly diamond-shaped cross section.

angular particles Grains, or particles, with shapes that are characterized by jaggedprojections, sharp ridges, and flat surfaces.

annular drainage pattern A ringlike drainage pattern formed in areas where sedimen-tary rocks are upturned by a dome structure.

anthracite A hard natural coal of high luster differing from bituminous coal in containing

anticline fold

AOS

APSB

AR

arcuate delta

argillaceous

little volatile matter.

Upfolds.

apparent opening size

asphalt penetration surface binder

Army regulation

Arc- or fan-shaped deltas formed when wave action is the primary force ac-ting on the deposited material.

Soils which are predominantly clay or abounding in clays or claylikematerials.

asphalt emulsions A blend of asphalt, water, and an emulsifying agent and is availableeither as anionic or cationic emulsions.

asphalt penetration surface binder A special liquid asphalt composed of high penetra-tion-grade asphalt and a solvent blend of kerosene and naphtha.

ASTM American Society of Testing and Materials

asymmetrical fold A fold with an inclined axial plane.

augite The most common of the pyroxenes.

B horizon The layer Containing soluble materials washed out of the A horizon. This layerfrequently contains much clay and may be several feet thick.

backfill TO refill (as an excavated area) usually with excavated material.

Glossary-2

FM 5-410

barchan dune The simplest and most common of dunes. Usually crescent-shaped. Thewindward side has a gentle slope rising to a broad dome that is cut offabruptly on the leeward side.

basalt Very fine-grained, hard, dense, dark-colored extrusive rock which occurs widely inlava flows around the world.

base exchange The process of replacing cations of one type with cations of another type inthe surface of an adsorbed layer.

batholith A great mass of intruded igneous rock that for the most part stopped in its riseto the earth’s surface at a considerable distance below the surface.

batter A receding upward slope of the outer face of a structure.

batter piles Those piles that are driven at an angle with the vertical They r-nay be used tosupport inclined loads or to provide lateral loads.

bearing capacity The soil’s ability to support loads which may be applied to it by an en-gineering structure.

bearing pile A pile driven into the ground so as to carry a vertical load.

bedded sediments Parallel layers of sediment lying one on top of the other.

bedding planes The surface that separates each successive layer of a stratified rock fromits preceding layer, a depositional plane, or a plane of stratification.

bed load Material too heavy to be suspended by erosional agents for great distances at anyone period of time. Consists mainly of coarse particles that roll along theground.

bentonite A clay of high plasticity formed by the decomposition of volcanic ash, which hashigh swelling characteristics.

bird’s-foot delta Resembles a bird’s foot from the air and is formed in instances wherefluvial processes have a major influence on deposited sediments.

bite test A quick and useful method of distinguishing among sand, silt, or clay. In thistest, a small pinch of the soil material is ground lightly between the teethand the grittiness determined.

bitumen-lime blend A system in which small percentages of lime are blended with fine-grained soils to facilitate the penetration and mixing of bitumens into thesoil.

blanket cover Any material that forms a (semi) permanent cover and is immovable by thewind it serves to control dust.

blind drainage Sections of a stream channel which are blocked at both ends.

boulder clay Another name, used widely in Canada and England, for glacial till.

Glossary-3

FM 5-410

braided drainage pattern A drainage pattern resulting from the dividing and reunitingof stream channels. The pattern commonly forms in arid areas duringflash flooding or from the meltwater of a glacier. The stream has at-tempted to carry more material than it is capable of handling.

breccia A rock consisting of sharp fragments cemented by finer-g-rained material.

breaking test

buckshot clay

Performed only on material passing the number 40 sieve. Used to measurethe cohesive and plastic characteristics of the soil.

Clay of the southern and southwestern United States which, upon drying,crack into small, hard lumps of more or less uniform size.

bulking of sands The volumetric increase in a dry or nearly dry sand caused by the intro-duction of a slight amount of moisture and disturbance of the soil.

buttress A projecting structure of masonry or wood for supporting or giving stability to a

C

C horizon The

wall or building; a projecting part of a mountain or hill; a broadened baseof a tree trunk or a thickened vertical part of it; something that supports orstrengthens.

celsius; centigrade; clay

weathered parent material.

calcareous Soils which contain an appreciable amount of calcium carbonate, usuallyderived from limestone.

calcite A soft, usually colorless to white mineral distinguished by a rapid bubbling or fizz-ing reaction with dilute hydrochloric acid. It is the major component of seashells and coral skeletons and often occurs as well-formed, glassy to dull,blocky crystals.

caliche The nitrate-bearing g-ravel or rock of the sodium nitrate deposits of Chile and Peru;a crust of calcium carbonate that forms on the stony soil of arid regions.

California Bearing Ratio A measure of the shearing resistance of a soil under carefullycontrolled conditions of density and moisture.

capillary fringe Capillary action in a soil above the ground water table.

capillary moisture When dry soil grains attract moisture in a manner somewhat sirnilarto the way clean glass does.

capillary saturation When the soil is essentially saturated.

carbonation

carbonic acid

The chemical process in which carbon dioxide from the air unites withvarious minerals to form carbonates.

A weak dibasic acid H2C03 known only in solution that acts to dissolve car-bonate rocks.

Glossary-4

FM 5-410

cavern An underground chamber often of large or indefinite extent.

CBR California Bearing Ratio

Cc coefficient of curvature

CE compactive effort

CE 55 compactive effort, 55 blows per layer

cementation This occurs when precipitates of mineral-rich waters, circulating through thepores of sediments, fill the pores and bind the grains together.

CH clays, highly compressive (LL>50)

chemical stabilization Relies on the admixture to alter the chemical properties of the soilto achieve the desired effect, such as using lime to reduce a soil’s plasticity.

chemical weathering The decomposition of rock through chemical processes. Chemicalreactions take place between the minerals of the rock and the air, water, oratmosphere.

chert A rock resembling flint and consisting essentially of cryptocrystalline quartz or amor-phous silica.

chlorite A very soft, grayish-green to dark green mineral with a pearly luster. It occursmost often as crusts, masses, or thin sheets or flakes in metamorphic rocks,particularly schists and greenstone.

cinder The slag from a metal furnace; a fragment of ash; a partly burned combustible inwhich fire is extinct; a hot coal without flame; a partly burned coal capableof further burning without flame; a fragment of lava from an erupting voi-cano.

CL clay, low compressibility (LL<50)

Class C fly ash Has a high CaO content (12 percent or more) and originates from sub-bituminous and lignite (soft) coal.

Class F fly ash Has a low CaO content (less than 12 percent) and originates fromanthracite and bituminous coal.

elastic sediments Deposit of rock particles dropped from suspension in air, water, or ice.

clay mineral Form soft microscopic flakes which are usually mixed with impurities ofvarious types (particularly quartz, limonite, and calcite). When barelymoistened, as by the breath or tongue, clays give off a characteristic some-what musty “clay” odor.

clay stone A calcareous concretion formed in a bed of clays; a dull earthy feldspathic rockcontaining clay.

Glossary-5

FM 5-410

cleavage The tendency of’ a mineral to split or separate along preferred planes whenbroken.

cm c e n t i m e t e r ( s )

c m3 cubic centimeter(s)

CMS concrete-modified cement

coal An accumulation and conversion of the organic remains of plants and animals undercertain environments.

coarse-grained rocks Those rocks that have either crystals or cemented particles that arelarge enough to be readily seen with the unaided eye.

coarse-grained soil Those soils in which half or more of the material is retained on aNumber 200 sieve.

compaction The reduction of volume and increase in density that results from the applica-tion of downward stress to a material. The stress moves the particlescloser together, reducing the volume of air voids and increasing the unitweight. (density) of the material.

competence The maximum size of particles capable of being moved b-y a stream.

complex dunes Dunes which lack a distinct form and develop where wind directions vary,sand is abundant, and vegetation may interfere. They occur locally whenother dune types become overcrowded and overlap.

compressibility That property of a soi1 which permits it to deform under the action of anexternal compressive load.

conchoidal fracture A fracture surface that exhibits concentric, bowl-shapd structureslike the inside of a clam shell.

conglomerates Rocks composed of rounded fragments varying from small pebbles to largeboulders held together by a natural cement.

contact moisture When water is brought into the capillary zone from the water table byevaporation and condensation.

continental glaciation Occurs on a large, regional scale affecting vast areas. Charac-terized by the occurrences of more depositional features than erosional fea-tures. The glaciers can be of tremendous thickness and extent.

coquina Consists essentially of marine shells held together by a small amount of calciumcarbonate to form a fairly hard rock. Coquina is widely used for thegranular stabilization of soils along the Gulf Coast of the United States.

coral Calcareous, rocklike material formed by secretions of corals and coralline algae. Thewhite type is very hard, while the gray type tends to be soft, brittle, and ex-tremely porous.

Glossary-6

FM 5-410

coral sand Consists of decomposed coral which may be combined with washed and sortedbeach sands.

crevasse filling A material contained within a deep crevice, or fissure, in a glacier or theearth.

cross-beds Individual layers within a bed that lie at an angle to the layers of adjacentbeds, typical of sand dune and delta front deposits.

CSS cationic slow-setting

cu cubic

c u coefficient of uniformity

cutback asphalt A blend of an asphalt cement and a petroleum solvent.

d desirable base and subbase material

daily mean temperature An average of the maximum and minimum temperatures forone day or an average of several temperature readings taken at equal timeintervals during the day, generally hourly.

DA Department of the Army

DBST double bituminous surface treatment

DCA 70 a polyvinyl acetate emulsion

DD Department of Defense

debris avalanche The rapid downslope flowage of masses of incoherent soil, rock, andforest debris with varying water content. They are shallow landslidesresulting from frictional failure along a slip surface, essentially parallel tothe topographic surface, formed where the accumulated stresses exceed theresistance to shear.

debris flows Occur when a debris avalanche increases in water content. They are causedmost frequently when a sudden influx of water reduces the shear strengthof earth material on a steep slope, and they typically follow heavy rainfall.

deflation Occurs when loose particles are lifted and removed by the wind. This results ina lowering of the land surface as materials are carried away.

degree days (As used in this FM) the difference between the average daily air tempera-ture and 32 degrees Fahrenheit. The degree days are minus when theaverage daily temperature is below 32 degrees Fahrenheit (freezing degreedays) and plus when above (thawing degree days).

delta The alluvial deposit at the mouth of a river.

delta kame Well-sorted glacial deposits made up of gravels and sands.

Glossary-7

FM 5-410

dendritic drainage pattern A treelike pattern composed of branching tributaries to amain stream. It is characteristic of essentially flat lying and/or relativelyhomogeneous rocks.

density The weight per unit volume.

desert pavement See “lag deposits.”

design freezing index The freezing index of the average of the three coldest winters in 30years of record, or of the coldest winter in a 10-year period, if 30-year dataare unavailable.

diatomaceous earth Corn posed essentially of the siliceous skeletons of diatoms (extremelysmall unicelled organisms). It is composed principally of silica, is white orlight gray in color, and is extremely porous.

diorite A granular crystal line igneous rock commonly composed of plagioclase andhornblende, pyroxene, or biolite.

dip The inclination of a bedding plane.

dirty sand A slightly silty or clayey sand.

DM draft manual

dolomite A mineral consisting of a calcium magnesium carbonate found in crystals, as wellas in extensive beds, as a compact limestone.

dome An upfold that plunges in all directions.

D r relative density

drag Folding of rock beds adjacent to a fault.

drumlins Asymmetrical streamlined hills of gravel till deposited at the base of a glacierand oriented in a direction parallel to ice flow.

dry density Weight of solid fraction of a soil material divided by the volume of the soilmaterial. Synonymous with dry unit weight.

dry strength test See “breaking test.”

durability The resistance to slaking or disintegration due to alternating cycles of wettingand drying or freezing and thawing.

dust palliative Material used tO prevent soil particles from becoming airborne.

e void ratio

E east

Glossary-8

FM 5-410

earthflow A landslide consisting of unconsolidated surface material that moves down aslope when saturated with water.

earth-retaining structure Used to restrain a mass of earth which will not stand unsup-ported.

earthquake A shaking or trembling of the earth that is tectonic in origin; movement alonga fault.

elongate delta Long, relatively narrow delta formed where tidal currents have a major im-pact on sediment deposition.

EM engineer manualemax void ratio in the loosest condition possibleemin void ratio in the most dense condition possibleen natural void ratio

end moraines Ridges of till material pushed to their locations at the limit of the glacier’sadvance by the forceful action of the ice sheet.

eolian Descriptive term implying action by wind.

EOS equivalent opening size

EPA Environmental Protection Agency

erosion The transportation of weathered materials by wind or water.

eskers Winding ridges of irregularly stratified sand and gravel that are found within thearea of the ground moraine created by continental glaciation.

evaporates Sedimentary rocks (as gypsum) that originated by evaporation of seawater inan enclosed basin.

exfoliation A type of weathering that involves the breaking loose of thin concentric shells,slabs, spans, or flakes from rock surfaces.

extrusive igneous rock Those rocks formed by extrusion from the earth in a molten stateor as volcanic ash.

F Fahrenheit; frictional resistance to sliding

FAA Federal Aviation Administration

fat clay Fine, colloidal clay of high plasticity; classified as (CH) by the USCS.

faults Fractures along which there is displacement of the rock parallel to the fractureplane. Once-continuous rock bodies that have been displaced by movementin the earth’s crust.

Glossary-9

FM 5-410

fault scarp A cliff or escarpment directly resulting from an uplift along one side of a fault.

fault zone An area in which there are several closely spaced faults.

feldspars Any of a group of crystalline minerals that consist of aluminum silicates witheither potassium, sodium, calcium, or barium; essential constituents ofnearly all crystalline rocks.

felsite A very fine-grained, usually extrusive igneous equivalent of granite.

FHWA Federal Highway Administration

fill saddles Narrow saddles used to hold hauled material.

filtration geotextiles Used when soils may migrate into drainage aggregate or pipe. Itprevents the soil migration and thus maintains water flow through thedrainage system.

fine-grained soil Those soils in which more thansieve.

fissility Capable of being split or divided in theplanes of cleavage.

FLS forward landing strips

fly ash Fine solid particles of ashes, dust, and soot

half the material passes a Number 200

direction of the grain or along natural

carried out from burning fuel (as coal oroil) by a draft. This pozzolanic material consists mainly of silicon andaluminum compounds that, when mixed with lime and water, forms a har-dened cementitious mass capable of obtaining high compression strengths.

FM field manual

foliated Metamorphic rocks that d display a pronounced banded structure as a result of thereformational pressures to which they have been subjected.

footwall The block below a fault plane.

fracture The way in which a mineral breaks when it does not cleave along cleavage planes.

fragipan See “hardpan.”

free water When the zone of saturation is under no pressure except from the atmosphere.

freezing index The number of degree days between the highest and lowest points on acurve of cumulative degree days versus time for one freezing season. It isused as a measure of the combined duration and magnitude of below-freezing temperature occurring during any given freezing season. Theindex determined for air temperatures at 4.5 ft above the ground is com-monly designated as the “air freezing index, ” while that determinedfor temperatures immediately below a surface is known as the “surfacefreezing index.”

Glossary-10

FM 5-410

frost action Processes which affect the ability of soil to support a structure when accumu-

frost boil The

lated water in the form of ice lenses in the soil is subjected to natural freez-ing conditions.

breaking up of a localized section of a highway or airfield pavement whensubjected to traffic. During the process of thawing, the melted waterproduces a supersaturated or fluid subgrade condition with very limited orno supporting capacity. The traffic imposes a force on the pavement andthus on the excess water in the subgrade, which in turn exerts an equaliz-ing pressure in all directions. This pressure is relieved through the pointof least resistance (up through the pavement surface) and produces a smallmound similar in appearance to an oversized boil.

frost heave An upthrust of ground caused by freezing of moist soil (as under a footing orpavement).

frost-melting period An interval of the year during which the ice in the foundationmaterials is returning to a liquid state. It ends when all the ice in theground is melted or when freezing is resumed. Although there is generallyonly one frost-melting period, beginning during the general rise of airtemperature in the spring, one or more significant frost-melting intervalsmay occur during a winter season.

frost-susceptible soil Soil in which significant ice segregation will occur when the neces-sary moisture and freezing conditions are present.

frothy A sample that appears pitted or spongy.

ft foot; feet

Fuller’s earth Unusuallycolor. Used

g gram(s)

highly plastic clays of sedimentary origin, white to brown incommercially to absorb fats or dyes.

G specific gravity; gravel

gabbro A granular igneous rock composed essentially of calcic plagioclase, a ferromag-nesian mineral, and accessory minerals.

gabbro-diorite A series of dense, coarsely crystalline, hard, dark-colored intrusive rockscomposed mainly of one or more dark minerals along with plagioclasefeldspar.

gabion Large, steel wire-mesh baskets usually rectangular in shape and variable in size.They are designed to solve the problem of erosion.

gal gallon(s)

galena A bluish gray mineral (PbS) with metallic luster consisting of lead sulfide, showinghighly perfect cubic cleavage, and constituting the principal ore of lead.

Glossary-11

FM 5-410

gap-graded Soil contains both large and small particles, but the gradation continuity isbroken by the absences of some particle sizes.

garnet A brittle and more or less transparent usually red silicate mineral that has avitreous luster, occurs mainly in crystals but also in massive form and ingrains, is found commonly in gneiss and mica schist, and is used as a semi-precious stone and as an abrasive.

GC clayey gravel

geogrid A geotextile that is constructed with relatively large openings that act to lock soilparticles in place (confining them) and adding strength to the soil.

glacial lake deposit Occurs during the melting of the glacier. Many lakes and ponds arecreated by meltwater in the outwash areas.

glaciofluvial Relating to, or coming from streams deriving much or all of their water fromthe melting of a glacier.

glassy Fine-grained rocks with a shiny smooth texture showing conchoidal fracture. An ex-ample is obsidian, a black volcanic glass.

GM silty gravel

gneiss A foliated metamorphic rock corresponding in composition to granite or some other

gouge Crushed

GP

graben A block

gradation The

feldspathic- plutonic rock. it is medium- to coarse-grained and consists ofalternating streaks or bands.

and altered rock.

poorly graded g-ravel

that is downthrown between two faults to form a depression.

distribution of particle sizes in the soil.

grain size See “particle size.”

granite A coarsely crystalline, hard, massive, light-colored rock corn posed mainly of feldsparand quartz, usually with mica and/or hornblende.

gravitational water See “free water.”

gravity fault See “normal fault.”

grit test See “bite test.”

ground moraine Glacial deposits that are laid down as the ice sheet recedes.

groundwater table The upper limit of the saturated zone of free water.

Glossary-12

FM 5-410

gumbo Peculiar, fine-g-rained, highly plastic, silt-clay soils which become pervious andsoapy, or waxy and sticky, when saturated.

GW well-graded gravel

H high compressibility

halite Rock salt.

hanging wall The block above a fault plane.

hardness The resistance to scratching or abrasion by other minerals or by an object ofknown hardness.

handpan A general term used to describe a hard, cemented soil layer which does not softenwhen wet and may be impervious to water.

hc height of capillary rise

HC1 hydrochloric acid

headwalls Bowl-shaped areas with slope gradients often 100 percent or greater. It isusually the junction for several intermittent streams that can cause sharprises in the groundwater levels in the soil mantle during winter storms.

hematite A mineral (Fe2O3) constituting an important iron ore and occurring in crystals orin a red earthy form.

homocline fold A rock body that dips uniformly in one direction (at least locally).

hornblende A mineral that is the common dark variety of aluminous amphibole.

horst An upthrown block between two faults.

hummocky terrain Terrain composed of many depressions and uneven ground.

hydration The chemical union of a compound with water.

hydrolysis A chemical process of decomposition involving splitting of water molecules andsubsequent reaction with various minerals.

hydrophytes A vascular plant growing wholly or partly in water especially a perennialaquatic plant having its overwintering bulbs underwater.

hydroscopic moisture The water adsorbed from atmospheric moisture when the soil is in—

igneous rocks

an air-dry condition.

Those rocks that have solidified from molten material which originateddeep within the earth’s mantle. This occurred either from magma in thesubsurface or from lava extruded onto the earth’s surface during volcaniceruptions.

Glossary-13

FM 5-410

impervious soils Fine-grained, homogeneous, plastic soils, and coarse-grained soils thatcontain plastic fines. Soils that do not allow for the transmission of sig-nificant amounts of water.

intrusive igneous rocks Those rocks that have cooled from magma beneath the earth’ssurface.

Ip plasticity index

joints Rock fractures along which there has been little or no displacement parallel to thefractured surface.

k coefficient of permeability; subgrade reaction

kames Conical hills of’ sand and gravel that were deposited by heavily laden glacialstreams that flowed on top of or off of the glacier.

kame terraces Roughly linear deposit of sand and gravel associated with alpine glaciation.

kaolin A fine, usually white clay that is used in ceramics and refractories as a filler or ex-tender.

kettle holes Pits formed by the melting of ice which had been surrounded by or embeddedin the moraine material.

kip kilopound (1,000 pounds)

L low compressibility

lag deposits Gravel and pebbles that, are too large to be carried by the wind and so ac-cumulate on the earth’s surface in the form of a sheet. They ultimatelycover the finer-grained material beneath and protect it from further defla-tion.

laterites A residual product that is red in color and has a high content of the oxides of ironand hydroxides of aluminum.

laterite soils Residual soils which are found in tropic regions. Many different soils are in-cluded in this category and they occur in many sections of the world. Theyare frequently red in color and in their natural state have a granular struc-ture with low plasticity and good trainability. When moistened with waterand remolded, they often become plastic and clayey to the depth disturbed.

latosols A leached red and yellow tropical soil.

lava A viscous

lb

LCF

Glossary-14

liquid that flows out a volcanic vent or from fissures along the flanks of avolcano. It can flow many miles from the crater vent. Molten material atthe earth’s surface.

pound(s)

lime-cement-fly ash

FM 5-410

lean clay Silty clays and clayey silts, generally of low to medium plasticity.

lignin A by-product of the manufacture of wood pulp.

limbs The sides of a fold as divided by the axial plane.

lime A dry white powder consisting essentially of calcium hydroxide.

lime-cement-fly ash A mixture of lime, cement, and fly ash used as a soil stabilization ad-mixture.

limestone A soft to moderately hard rock that is formed chiefly by accumulation of organicremains (as shells or coral), consists mainly of calcium carbonate, is exten-sively used in building, and yields lime when burned.

linonite A native hydrous ferric oxide of variable composition that is a major ore of iron.Occurs most often as soft, yellowish-brown to reddish-brown fine-grainedearthy masses or compact lumps or pellets. It is a common and durablecementing agent in sedimentary rocks and the major component of laterite.

LL liquid limit

LM light duty mat

LMS lime-modified soil

loam A general agricultural term, applied most frequently to sandy-silty topsoils whichcontain a trace of clay, are easily worked, and support plant life.

loess Thick accumulations of yellowish-brown material composed primarily of windblownsilt. The silty soil is of eolian origin characterized by a loose, porous struc-ture, and vertical slope. It covers extensive areas in North America (espe-cially in the Mississippi Basin), Europe, and Asia (especially north-centralEurope, Russia, and China).

longitudinal dune A dune elongated in the direction of the prevailing winds.

LOTS logistics-over-the-shore

luster The appearance of a mineral specimen in reflected light. It is either metallic or non-metallic.

M silt

M2 a type of compass

magma Molten rock material within the earth.

magnetite A black isometric mineral of the spinal group that is an oxide of iron and an im-portant iron ore.

Glossary-15

FM 5-410

marble A soft, fine to coarsely crystalline, massive metamorphic rock which forms fromlimestone or dolomite. It is distinguished by its softness, acid reaction, lackof fossils, and sugary appearance on freshly broken surfaces.

marl A soft, calcareous deposit mixed with clays, silts, and sands, often containing shells ororganic remains. It is common in the Gulf Coast area of the United States.

mature stream Has a developed floodplain and, while the stream. no longer fills the entirevalley floor, it meanders to both edges of the valley.

max maximum

MB mechanical blending

MBST multiple bituminous surface treatment

MC medium curing

mean freezing index The freezing index determined on the basis of mean temperatures.Temperatures are usually averaged over a minimum of 10 years andpreferably 30 years.

mean temperature The average temperature for a given time period, usually a day, amonth, or a year.

mechanical stabilization Relies on physical processes to stabilize the soil, either alteringthe physical composition of the soil (soil blending) or placing a barrier in oron the soil to obtain the desired effect (such as establishing a Sod cover toprevent dust generation).

meniscus Curved upper surface of a water column.

metamorphic rock Those rocks that have been altered in appearance and physicalproperties by heat, pressure, or permeation by gases or fluids.

METT-T mission, enemy, troops, terrain, and time available

MH silt, highly compressible (LL<50)

mica Any of various colored or transparent mineral silicates crystallizing in monoclinicforms that readily separate into very thin sheets.

micaceous soil Soil that contains a sufficient amount of mica to give it distinctive ap-pearance and characteristics.

MIL-STD military standard

min minimum

mineral A naturally occurring, inorganically formed substance having an ordered internalarrangement of atoms. It is a compound and can be expresed by a chemi-cal formula.

Glossary-16

FM 5-410

ML silts, low compressibility (LL<50)

mm millimeter(s)

MM medium duty mat

MMC minimum moisture content

Mohs' Hardness Scale A simple scale used to measure the hardness of a mineral.

MO-MAT A commercial material used as an expedient surface.

monocline fold A rock body that exhibits local step-like slopes in otherwise flat or gentlyinclined rock layers. Common in plateau areas where beds may locally as-sume dips up to 90 degrees.

mountain glaciation See “Alpine glaciation.”

moraine An accumulation of earth and stones carried and finally deposited by a glacier.

MSDS Material Safety Data Sheet

muck (mud) The very soft, slimy silt or organic silt frequently found on lake or river bot-toms.

mud cracks Polygonal cracks in the surface of dried-out mud flats.

mudstone An indurated shale produced by the consolidation of mud. Primarily a fieldterm used to temporarily identify fine-g-rained sedimentary rocks of un-known mineral content.

mulch A protective covering (as of sawdust, compost, or paper) spread or left on the groundespecially to reduce evaporation, maintain even soil temperature, preventerosion, control weeds, or enrich the soil.

multilayer pavement A pavement that consists of at least two layers, such as a base andwearing course, or three layers, such as a subbase, base, and wearingcourse.

muskeg Peat deposits found in northwestern Canada and Alaska.

N north; normal force or interlocking force. The fraction of the weight of anobject that rests on a surface.

naphtha Any of various volatile often flammable liquid hydrocarbon mixtures used chieflyas solvents and dilutents.

NAVFAC

NE

NIOSH

Naval Facilities Engineering Command

northeast

National Institute of occupational Safety and Health

Glossary-17

FM 5-410

no number

nonfoliated Massive metamorphic rocks that exhibit no directional structural features.

nonfrost-susceptible materials Crushed rock, clean sandy gravel, slag, cinders, or anyother cohesionless material in which ice segregation does not occur undernatural freezing conditions. Uniformly graded soils, containing less than10 percent of grains smaller than 0.02 mm are nonfrost-susceptible. Well-graded soils containing less than 3 percent by weight smaller than 0.02mm are nonfrost-susceptible. In soils with less than 1 percent of grainssmaller than 0.02 mm, ice lenses will not form under field conditions.

normal fault Faults along which the hanging wall has been displaced downward relativeto the foot wall. Common where the earth’s surface is under tensionalstress so the rocks are pulled apart. Characterized by high angle (near ver-tical) fault planes.

NSN national stock number

nuclear moisture density tester An instrument that provides real-time, in-place mois-ture content and density measurements of a soil.

NW northwest

o organic soil

obsidian A hard, shiny, usually black, brown, or reddish volcanic glass which may containscattered gas bubbles or visible crystals.

odor test A test used to determine if a soil is organic. A strong odor indicates an organicsoil.

off-site admixing This is done when in-place admixing is not desirable and/or soil fromanother source provides a more satisfactory treated surface. This can beaccomplished with a stationary mixing plant, or by windrow-mixing withgraders in a central working area.

OH organic soil, highly compressible (LL > 50)

oiled earth An earth-road system made resistant to water absorption and abrasion bymeans of a sprayed application of slow-or medium-curing liquid asphalts.

OL organic soil, low compressibility (LL 50)

old-age stream A stream in which the gradient is very gentle, the water velocity is low,there is little downcutting, and lateral meandering produces an extensivefloodplain.

olivine A very hard, dense mineral which forms yellowish-green to dark olive-green orbrown glassy grains or granular masses. It is often found in very dark,iron-rich rocks, particularly gabbro and basalt.

Glossary-18

FM 5-410

OMC optimum moisture content

organisms Living creatures, plants, animals, and microorganisms. The acids produced bytheir life processes hasten the decomposition of rock masses near the sur-face. The wedging action caused by plant root growth hastens the disin-tegration process.

outwash plains Result when melting ice at the edge of the glacier creates a great volumeof water that flows through the end moraine as a number of streams ratherthan a continuous sheet of water.

overthrust fault Low-angle (near horizontal) reverse faults.

oxidation The chemical union of a compound with oxygen.

paneling Solid barrier fences of metal, wood, plastic, or masonry used to stop or divertsand movement.

parabolic-shaped dunes Crescent-shaped dunes with two tips that point upwind. Theytypically form along coastlines where the vegetation partially covers thesand or behind a gap in an obstructing ridge.

parallel drainage pattern Drainage pattern characterized by major streams trending inthe same direction. They indicate gently dipping beds or uniformly slopingtopography.

particle size Sizes of individual grains as determined by the use of sieves.

PBS prefabricated bituminous surfacing

pcf pound(s) per cubic foot

peat A term which is frequently applied to fibrous, partially decayed organic matter or a

pedology The

soil which contains a large proportion of such materials. Large and smalldeposits of peat occur in many areas and present many construction dif-ficulties. Peat is extremely loose and compressible.

study of the maturing of soils and the relationship of the soil profile to theparent material and its environment.

pegmatite A coarse variety of granite occurring in dikes or veins.

PEL permissible exposure limit

perched water table A localized zone of saturated soil above the normal ground watertable; created by the localized presence of relatively impervious soil layers.

period of weakening An interval of the year which starts at the beginning of the frost-melting period and ends when the subgrade strength has returned to nor-mal period values.

Glossary-19

FM 5-410

peridotite Any of a group of granitoid igneous rocks composed of ferromagnesian minerals,especially olivine.

permeability The property of soil which permits water to flow through it.

PF permafrost

physical weathering The disintegration of rock Rock masses are broken into smallerand smaller pieces without altering the chemical composition of the pieces.

PI plasticity index

pier foundation A type of support normally used only for very heavy loads.

pile foundation A load-bearing member which may be made of timber, concrete, or steel.It is generally forced into the ground.

pistol-butted trees Downslope-tipped trees that are small as a result of sliding soil ordebris or as a result of active soil creep. They are a good indicator of slopeinstability for areas where rain is a major component of winter precipita-tion.

pit-run coral Consists of fragmental coral in conjunction with sands and marine shells.

PL plastic limit

plagioclase A triclinic feldspar.

plasticity The ability of a soil to deform without cracking or breaking.

plasticity index The difference between the liquid and plastic limits.

plastic limit The lowest moisture content at which a soil can be rolled into a thread 1/8inch in diameter without crushing or breaking.

platy grains Extremely thin grains, compared to their lengths and widths. They have the

plunging fold

POL

precipitates

prefabricated

psi

Pt

general shape-of a flake of mica or a sheet of paper.

Folds that dip back into the ground at one or both ends.

petroleum, oils, and lubricants

Salts that have become insoluble, separated from solution, and beendeposited.

mesh Heavy woven jute mesh, such as commonly used in conjunction withgrass seed operations; can be used for dust control of’ nontraffic areas.

pounds per square inch

peat soil

Glossary-20

FM 5-410

pumice A volcanic rock full of cavities and very light in weight; used especially in powderform for smoothing and polishing.

pyrite A common mineral that consists of iron disulfide (FeS2), has a pale brass-yellowcolor and metallic luster, and is burned for the manufacture of sulfurdioxide and sulfuric acid.

pyroclastics Volcanic materials that have been explosively ejected from a vent.

pyroxene Hard, dense, glassy to resinous minerals found chiefly in dark igneous rocks—and, less often-, in dark gneisses and schists. They usually occurformed short, stout, columnar crystals that appear almost squaresection.

quarry An open excavation made into rock masses by drilling, cutting, or blasting.

as well-in cross

quartz An extremely hard, transparent to translucentluster.

quartzite A compact granular rock composed of quartzmetamorphism. It is an extremely hard,rock that forms from sandstone.

quick silts Very fine sands and silts that are compactedtable that pump water to the surface.

mineral with a glassy or waxy

and derived from sandstone byfine- to coarse-grained massive

in the presence of a high water

radial drainage pattern Acentral area.

rakes Inclined braces used to

RC rapid curing

drainage pattern in which streams flow outward from a highNormally found

support wales.

recessional moraines Sediments depositedable period of time.

on domes, volcanic cones, or rounded hills.

when a receding glacier halts for a consider-

recrystallization To recrystallize again or repeatedly.

rectangular drainage pattern A drainage pattern characterized by abrupt 90-degreechanges in stream directions. It is caused by faulting or jointing of the un-derlying bedrock.

recumbent fold A fold with an axial plane that has been inclined to the point that it ishorizontal.

residual soil Unconsolidated deposits resulting from the weathering of rock material inplace.

resins Dust palliative used as either surface penetrants or surface blankets; usually ligninbased.

Glossary-21

FM 5-410

retaining walls Constructed for the purpose of supporting a vertical or nearly verticalearth bank that, in turn, may support vertical loads.

reverse fault Results when the hanging wall of a fault becomes displaced upward relativeto the foot wall. These are frequently associated with compressional forceswhich accompany folding.

ripple marks Parallel ridges formed in some sediments. They may indicate the directionof wind or water movement during deposition.

road tar Viscous liquids obtained by distillation of crude tars extracted from coal.

rockfall A mass of falling or fallen rocks.

rock flour Finely ground rock particles, chiefly silt-sized, resulting from glacial abrasion.

rock riprap A foundation or sustaining wall of stones or chunks of concrete throwntogether without order (as in deep water); a layer of this or similarmaterial on an embankment slope to prevent erosion.

rockslide A usually rapid downward movement of rock fragments that slide over an in-c1ined surface.

rounded particles Those in which all projections have been removed and few ir-regularities in shape remain. They approach spheres of varying sizes.

rough tillage Uses chisel, luster, or turning plows to till strips across nontraffic areas.This method works best with cohesive soi1s that form clods.

RS rapid setting

RT road tar

RTCB road tar cutback

S south; degree of saturation; sand; permissible stress

SA soil-asphalt

saddles Low points on a ridge or crest line, generally a divide between the heads ofstreams flowing in opposite directions.

sag pond A slump block depression that fills with water during the rainy season.

salt solutions Water saturated with sodium chloride or other salts applied to sand dunesto control dust.

sand dune A hill or ridge of sand piled Up by the wind commonly found along shores, alongsome river valleys, and generally where there is dry surface sand duringsome part of the year.

Glossary-22

FM 5-410

sand grid A honeycomb shaped geotextile measuring 20 feet by 8 feet by 8 i riches deepwhen fully expanded. It is used to develop a beachhead for logistics-over-the-shore operations. It is also useful in expedient revetment construction.

sandstone A hard elastic sedimentary rock composed mainly of sand-size (1/26 mm to 2mm) quartz grains, often with feldspar, calcite, or clay.

SBST single bituminous surface treatment

SC slow curing; soil-cement

schist Metamorphic crystalline rock having a closely foliated structure allowing divisionalong approximately parallel planes. It is a fine- to coarse-grained rockcomposed of discontinuous thin layers of parallel mica, chlorite,hornblende, or other crystals.

SCIP scarify/compact in-place

scoria Rough vesicular cindery lava, common in volcanic regions and generally forms overbasaltic lava flows. It is somewhat denser and tougher than pumice, andthe gas bubbles which give it its spongy or frothy appearance are generallylarger and more widely spaced that those in pumice.

SCS Soil Conservation Service

SE southeast

sedimentary rock Formed of mechanical, chemical, or organic sediment, such as rock

seepage force

shale A fissile

formed of fragments transported from their source and deposited elsewhereby water (as sandstone or shale); rock formed by precipitation from solu-tion (as rock salt or gypsum); rock formed from inorganic remains of or-ganisms (as limestone comprised of shells and skeletons)

The drag force that moving water exerts on each individual soil particle inits path.

rock that is formed by the consolidation of clay, mud, or silt, has a finelystratified or larninated structure, and is composed of minerals essentiallyunaltered since deposition.

shearing When one portion of a block of uniform soil fails, or slides, past another portion ina parallel direction.

shear planes or plane of failure The surface along which shearing action takes place.

shear strength The resistance to shearing.

shelter belts Barriers formed from hedges, shrubs, or trees which are high and denseenough to significantly reduce wind velocities on the leeward side.

shrinkage Reduction in volume when the moisture content of a soil is reduced.

Glossary-23

FM 5-410

shrinkage limit The moisture content a which a soil occupies the boundary between thesemisolid and solid states.

sieve A device with meshes or perforations through which finer particles of’ a mixture (as ofashes, flour, or sand) of various sizes are passed to separate them fromcoarser ones, through which the liquid is drained from liquid-containingmaterial, or through which soft materials are forced for reduction to fineparticles.

silicon dioxide See “quartz.”

single-layer pavement A stabilized soil structure on a natural subgrade.

siltstone A rock composed chiefly of indurated silt.

sinkhole A depression in which drainage collects and communicates with a cavern or pas-

SL

slaking

slate A

Slumps

sage. Normally located in regions underlain by limestone.

soil lime

test Used to assist in determining the quality of certain shales and other soft rock-like materials. The test is performed by placing the soil in the sun or in anoven to dry and then allowing it to soak in water for a period of at least 24hours. The strength of the soil is then examined. Certain types of soil willcompletely disintegrate, losing all strength.

dense fine-grained metamorphic rock produced by heat and pressure action onshales so as to develop a characteristic cleavage.

Slope failures where one or more blocks of soil have failed on a hemispherical, orbowl-shaped, slip surface; they may show varying amounts of backwardrotation into the hill in addition to downslope movement. They usuallyoccur in deep, moderately fine or fine-textured soils that contain a sig-nificant amount of silt or clay.

slurry A watery mixture of insoluble matter (as mud, lime, or plaster of paris).

SM silty sands and poorly graded sand-silt mixture

SP poorly graded sand

soil The entire unconsolidated material that overlies and is distinguishable from bedrock.It is composed principally of the disintegrated and decomposed articles ofrock.

soil creep A relatively slow-moving type of slope failure.

spall To break up (ore) with a hammer usually preparatory to crushing; to reduce (as ir-regular stone blocks approximately to size by chipping with a hammer; tocause to break off in spans; to break off chips, scales, or slabs from the sur-face or edge often as the result of a rapid change of temperature; to split offparticles as the result of bombardment in such a manner that a large part

Glossary-24

FM 5-410

remains used of a surface, target, or nucleus. A fragment removed from arock surface by weathering (few exfoliation detach themselves from. theparent mass in the form of lenses).

specific gravity The ratio of a substance weight (or mass) to the weight (or mass) of anequal volume of water.

“speedy" moisture content test An accurate test providing a very rapid moisture contentdetermination.

S-S silica-sesquioxide ratio

SS slow setting

stability The ability of a soil to support loads.

stoss side The side from which ice flows.

stratified glacial deposit A glacial deposit consisting of layered sediments.

stratified rock See “sedimentary rock”

strike The trend of the line of intersection formed between a horizontal plane and the bed-ding plane being measured.

strike slip fault A fault that is characterized by one block being displaced laterally withrespect to the other; there is little or no vertical displacement.

subangular particles Those particles that have been weathered until the sharper pointsand ridges of the original angular shape have been worn off.

surrounded particles Those particles that have undergone considerable weathering sothat they are somewhat irregular in shape and have no sharp corners andfew flat areas.

surface blanket A blanket cover over the soil surface to control dust. Materials used tQform the blanket include aggregates, prefabricated membranes and mesh,bituminous surface treatments, polyvinyl acetates (with or withoutfiberglass scrim reinforcements) and polypropylene - asphalt membranes.

suspended load That portion of material within a transporting medium that is lifted farfrom the earth’s surface, is sustained for long periods of time, and is dis-tributed through the entire body of the current.

symmetrical fold A fold with a vertical or near-vertical axial plane.

synclinal fold Downfolds.

SW well-graded sand; southwest

talus A fan-shaped accumulation of mixed fragments of rock that have fallen because ofweathering of a cliff or steep mountainside.

Glossary-25

FM 5-410

tension cracks Those cracks that relieve stress in the soil mantle.

terminal moraines See “end moraines.”

texture The relative size and arrangement of the mineral grains making up a rock.

throw The vertical displacement along a fault.

thrust fault Reverse faults that dip at low angles (less than 15 degrees) and havestratigraphic displacements commonly measured in kilometers.

till Unstratified glacial drift consisting of clay, sand, g-ravel, and boulders intermingled.

till plains See “ground moraine.”

TLV threshold limit value

TM technical manual

TO theater of operations

topsoil A general term applied to the top few inches of soil deposits. Topsoils usually con-tain considerable organic matter and produce plant life.

toughness A rock’s resistance to crushing or breaking.

transported soil Materials that have been transported and deposited at a new location byglacial ice, water, or wind.

tranverse dune Wavelike ridges formed perpendicular to prevailing wind direction andseparated by troughs. They resemble sea waves during a storm.

trellis drainage pattern A drainage pattern in which tributaries generally flow parallelto the main streams, eventually joining them at right angles.

trenching The cutting of a trench either transversely or longitudinally across a dune todestroy its symmetry.

tuff A term applied to compacted deposits of the fine materials ejected from volcanoes, suchas more or less cemented dust and cinders. Tuffs are more or less stratifiedand in various states of consolidation. They are prevalent in the Mediter-ranean area.

u undesirable base and subbase material

uniformly graded soils Soil consists primarily of particles of nearly the same size.

unloading A form of physical weathering that results from the relief of pressure on a rockunit due to the removal of overlying materials.

unstratified glacial deposit Heterogeneous mixtures of different particle types and sizesranging from clays to boulders that were directly deposited by glacial ice.

Glossary-26

FM 5-410

u s United States

USCX Unified Soil Classification System

v total volume; unit weight

Va volume of air

varved clay A sedimentary deposit which consistsclay.

vegetative treatment Method of soil stabilization.

Vol volume

of alternating thin layers of silt and

volcanic ash Uncemented volcanic debris, usually made up of particles less than 4 mm indiameter. Upon weathering, a volcanic clay of high compressibility is fre-quently formed. Some volcanic clays present unusually difficult construc-tion problems, as do those in the area of Mexico City and along the easternshores of Hawaii.

vm wet unit weight; wet density

vs volume of solids

vv volume of voids

Vw volume of water

w moisture content

W total weight; west

wales A horizontal constructionalmembers.

wd dry weight

member (as of timber or steel) used for bracing vertical

weathering The physical or chemical breakdown of rock. It is the process by which rock isconverted into soil.

well-drained soil Soils that allow for the significant transmission of water (essentiallyclean sands and gravels).

well-graded soil Has a good representation of all particle sizes from the largest to thesmallest and the shape of the grain-size distribution curve is considered“smooth.”

wet density The weight of a soil material (including moisture fraction) divided by thevolume of the soil material. Synonymous with wet unit weight and fielddensity.

Glossary-27

FM 5-410

WL

Wp

ws

ww

yd

liquid limit

plastic limit

weight of solids

weight of water

yard(s)

Glossary-28

C1, FM 5-410

Glossary-29

ADM area defense management

alidade In plane tabling, a straight edge having a telescopic sight or other means ofsighting parallel to it.

aquifer Any geologic formation containing water.

artesian Refers to ground water confined under hydrostatic pressure.

ASCS Agricultural Stabilization and Conservation Service

attitude The position of a structural surface relative to the horizontal and expressedby the strike and dip.

bedrock The lowest level of unbroken, solid rock. It is overlaid in most places by soilor rock fragments.

borings The chips, fragments, or dust produced in drilling or driving a hole into theearth’s surface.

bpi bits per inch

cobble A rock fragment larger than a pebble and smaller than a boulder (64 to 256millimeters in diameter) that is somewhat rounded or otherwisemodified by abrasion in the course of transport.

conglomerates Rocks composed of rounded fragments, varying from small pebbles tolarge boulders, and held together by a natural cement.

contour line A line connecting points of equal elevation above or below a datumplane.

CP command post

DC District of Columbia

DIA Defense Intelligence Agency

EROS Earth Resources Observation System

ERTS Early Remote Tracking System

fluvial Pertaining to rivers and streams.

geology The science that deals with the physical history of the earth, rocks thatcompose the earth, and the physical changes that the earth hasundergone or is undergoing.

geomorphology The origin and development of the topography of the continents.

geophysical exploration Locating and studying underground deposits of ores,mineral, oil, gas, and water.

geosyncline A downward trough of the earth’s crust where sediment accumulates.

HCl hydrochloric

C1, FM 5-410

Glossary-30

hydrogeologic Refers to geologic features that may indicate the presence of water.

hydrologic cycle A cycle in which water is evaporated from the sea, then precipitatedfrom the atmosphere to the surface of the land, and finallyreturned to the sea by rivers and streams.

IR infrared

LANDSAT land satellite

leaching The process where the more soluble compounds are removed by percolatinggroundwater.

lithification Conversion of unconsolidated sediments into solid rock.

m meter(s)

MSS Multispectral Scanner System

photogeology The art and science of using photo images to determine the geology ofan area.

plane table A drawing board mounted on a tripod. It is used in the field for obtainingand plotting survey data.

PO post office

porosity. The state or quality of being porous, expressed as a percentage of the volumeof the pores of a rock to the total volume of its mass.

rhyolite A fine-grained igneous rock that is rich in silica. The volcanic equivalent ofgranite.

schist Metamorphic crystalline rock having a closely foliated structure that allowsdivision along approximately parallel planes. A fine- to coarse-grained rock that is composed of discontinuous thin layers ofparallel mica, chlorite, hornblende, or other crystals.

SD South Dakota

SLAR side-looking radar

stratigraphic sequence The classification, correlation, and interpretation ofstratified rocks.

topography The relief features or surface configurations of an area.

USGS United States Geological Survey

UT Utah

FM 5-410

R e f e r e n c e s

Sources Used

These are the sources quoted or paraphrased in this publication.

Joint and Multiservice Publications

FM 5-430-00-1/AFP 93-4, Volume I. Planning and Design of Roads, Airfields, and Heliportsin the Theater of Operations: Road Design, To be published within 6 months,

FM 5-430-00-2/AFP 93-4, Volume II. Planning and Design of Roads, Airfields, andHeliports in the Theater of Operations: Airfield and Heliport Design. To be publishedwithin 6 months,

TM 5-530. Materials Testing, (NAVFAC MO-330/AFM 89-3) 17 August 1987.TM 5-803-13, Landscape Design and Planting Criteria, (AFM 126-8) August 1988.TM 5-822-2. General Provisions and Geometric Design for Roads, Streets, Walks, and Open

Storage Areas. (NAVFAC DM5.5: AFM 88-7, Chapter 5). 14 July 1987,TM 5-822-4. Soils Stabilization for Pavements. (AFM 88-7, Chapter 4). 1 April 1983. TM

5-822-5. Engineering and Design: Flexible Pavements for Roads, Streets, Walks, andOpen Storage Areas. (AFM 88-7, Chapter 3) 1 October 1980.

TM 5-822-8. Bituminous Pavements Standard Practice. (AFM 88-6, Chapter 9) 30 July1987.

TM 5-830-3. Dust Control for Roads, Airfields, and Adjacent Areas. (AFM 88-17, Chapter3). 30 September

Army Publications

FM 5-446. Military Nonstandard Fixed Bridging. 3 June 1991.TM 5-330. Planning and Design of Roads, Airbases, and Heliports in the Theater of

Operations. 6 September 1968 (To be superseded by FM 5-430).TM 5-337. Paving and Surfacing Operations. 21 February 1966.TM 5-331A. Utilization of Engineer Construction Equipment, Volume A: Earthmoving,

Compaction, Grading, and Ditching Equipment. 18 August 1987.TM 5-545. Geology, 8 July 1971.AR 420-74, Natural Resources: Land, Forest, and Wildlife Management. 1 July 1977.Mil Std 621A. Test Methods for Pavement Subgrade, Subbase, and Base Course Materials.

22 December 1964.EM 1110-2-1901. Seepage Analysis and Control for Dams. 30 September 1986.NAVFAC DM 7.1. Design. 1985.Special Report 83-27. Revised Procedures for Pavement Design Under Seasonal Frost

Conditions, US Army Corps of Engineers. September 1983. Office of the Chief ofEngineers, Washington, DC 20314.

Nonmilitary Publications

American Society of Testing and Materials (ASTM) D1633. Compression Strength of MoldedSoils Cementing Cylinders. 1990.

References-1

FM 5-410

Paeth, R, C., M.E. Harward, E.G. Knox, and C.T. Dyrness. Factors Affecting Mass Movementof Four Soils in the Western Cascades of Western Oregon. Soil Science Society of America,vol. 35.1971:943-947.

Swanston, D.N. Mass Wasting in Coastal Alaska, US Department of Agriculture, ForestService, Pacific Northwest Forest and Range Experiment Station, Research Paper,PNW-83. 1969:15.

Swanston, D.N. Mechanics, US Department of Agriculture, Forest Service, PacificNorthwest Forest and Range Experiment Station, Research Paper, 1970.

Documents Needed

These documents must be available to the intended users of this publication.

Army Publication

DD 1207. Grain Size Distribution Graph - Aggregate Grading Chart. 1 August 1957.DD 1211. Soil Compaction Test Graph/Swell Data. December 1986.DD 2463. California Bearing Ratio (CBR) Analysis, December 1986.ENG 4334, Plasticity Chart. June 1970,

References-2

FM 5-410

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FM 5-41023 DECEMBER 1992

By Order of the Secretary of the Army:

Official:

GORDON R. SULLIVANGenera/, United States Army

Chief of Staff

MILTON H. HAMILTONAdministrative Assistant to the

Secretary of the Army02939

DISTRIBUTION:Active Army, USAR, and ARNG: To be distributed in accordance with DA Form 12-11-E,requirements for FM 5-410, Military Soils Engineering (Qty rqr blk no. 3832).

* U.S. GOVERNMENT PRINTING OFFICE: 1993 728-027/60074