~Effects of Nanhamageneaus Cementatian...grain contact. They are generally quite difficult to sample, but arti-ficially cemented sands have been shown to aptly model the behavior of

~Effects of Nanhamageneaus Cementatian '·

in Sails

an Resistance ta Earthquake Effects/

by

Barry Scott Milstone ·.~

Thesis submitted to the Faculty of the

Virginia Polytechnic Institute and State University

in partial fulfillment of the requirements for the degree of

Master of Science

in

Civil Engineering

APPROVED:

J. Michael Duncan Thangavelu Kuppusamy

May, 1985

Blacksburg, Virginia

Effects of Nanhamageneaus Cementatian

in Sails

an Resistance ta Earthquake Effects

by

Barry Scott Milstone

G. Wayne Clough, Chairman

Civil Engineering

(ABSTRACT)

Small amounts of cementation in a sand increase its ability to sustain

static and dynamic loads, even in a liquefaction type environment. This

has been shown in previous research examining the behavior of both na-

turally cemented and artificially prepared samples.

Cemented sands are present in many parts of the world and can be caused

by either a variety of cementing agents or by cold welding at points of

grain contact. They are generally quite difficult to sample, but arti-

ficially cemented sands have been shown to aptly model the behavior of

natural materials, and allow for better test controls. Consequently,

artificial samples were used exclusively for the present investigation

which has three major objectives: to investigate the effects of a weakly

cemented lens within a stronger mass; to determine how cementation affects

the volume change characteristics of statically loaded samples; and, to

describe the pore pressure generation of sands subjected to cyclic load-

ing.

Prior to commencing the test program, a number of index tests were per-

formed on the uncemented and cemented sand used during the laboratory

investigation. It was revealed that cementation leads to increased void

ratios which distort relative density calculations used to compare ce-

mented and uncemented samples of similar dry unit weight. The practice

of identifying samples by dry unit weight was adopted for this report.

Static triaxial compression tests were performed on 17 samples. Test

results indicate that although the magnitude of volumetric strain at

failure does not seem to be dictated by the level of cementation, there

is a relationship with cementation and the rate of volume change at

failure. A weak lens was seen to lower the static strength of the

stronger mass. 26 stress controlled cyclic triaxial tests revealed that

a weak lens lowers the liquefaction resistance of the stronger mass. The

cyclic strength of the nonhomogeneous material, however, is higher than

the independent strength of the weak lens. A weak lens has greater in-

fluence at relatively higher levels of cyclic stress. Pore pressure

generation in cemented sands are seen to be controlled by strain. At

shear strain levels below about 1%, cemented sands behave similarly to

uncemented sands with pore pressures increasing more rapidly beyond that

amount of strain. Consequently, pore pressure development during cyclic

loading is described by a broken-back curve which is defined in the early

stages by existing empirical relationships for uncemented sand. Pore

pressure prediction may then be achieved using an equation for cemented

sand, such as that developed in the present work.

ACKNOWLEDGEMENTS

I am humbly grateful to all from whom I have learned during my long and

fortunate journey here.

Special thanks is extended to my advisor, Dr. G. Wayne Clough, for pro-

viding critical insight, encouragement, and a high professional standard.

I would also like to thank committee members, Dr. T. Kuppusamy and Dr. J.

Michael Duncan, for their parts in my education and help during this re-

search.

A grateful acknowledgement is extended to the National Science Foundation

Earthquake Hazard Mitigation Program for their sponsorship of this

reasearch project.

For their important friendship, perspective, and academic and technical

synergy, I thank my fellow students. I shall most fondly remember Al

Sehn, Vern Schaefer and their families, Terese Kwiatkowski, Jotaro

Iwabuchi, Sybil "Hatch, and Phillipe Mayu. The varied help extended to

me during my study in Blacksburg by Civil Engineering staff members,

particularly Vickie Graham and Judy Brown is greatly appreciated.

My greatest thanks goes to my family for their unwavering love and belief

in me, and for their support of any and all of my endeavors.

Acknowledgements iv

TABLE OF CONTENTS

1.0 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . .

2.0 BACKGROUND . . . . . . . . . . . . . . . . . . . . . . . . . 2. 1 CEMENTED SOILS

2.2 CEMENTED SAND DEPOSITS

2.3 STATIC BEHAVIOR OF WEAKLY CEMENTED SANDS

2. 4 LIQUEFACTION . . . . • . . • . • . . • . •

2.5 CYCLIC BEHAVIOR OF WEAKLY CEMENTED SAND

2.6 SUMMARY

3.0 EXPERIMENTAL INVESTIGATION

3. 1 INTRODUCTION . . . . . • .

3.2 ARTIFICIALLY PREPARED SAMPLES

3.3 MATERIALS USED

3.4 INDEX TESTING

3.4.1 Specific Gravity

3.4.2 Maximum Index Void Ratio

3.4.3 Minimum Index Void Ratio

3.4.4 Use of Index Properties

3.5 STATIC TESTS

3.6 CYCLIC TESTS

. . . . . . . . . . . .

4.0 SAMPLE PREPARATION . . . . . . . . . . . . . . . . . . . . . Table of Contents

1

3

3

4

5

9

10

13

16

16

17

18

19

22

22

23

25

26

27

29

v

4.1 USE OF THE RAINER

4.2 HOMOGENEOUS SAMPLES

4.3 NONHOMOGENEOUS SAMPLES

4.4 SATURATION •...•

S.O TEST PROGRAM, METHODS, AND EQUIPMENT . . . . . . . . . . 5.1 INTRODUCTION . • • . • • .••.

5.2 STATIC TESTING

5.2. 1 Introduction

5.2.2 Consolidated Drained Triaxial Testing and Equipment

5.3 CYCLIC TESTING ..••..•..•.

5.3.1 Introduction

5.3.2 Method of Loading •••.

5.3.3 Typical Results and Verification of Procedure

6.0 STATIC BEHAVIOR OF CEMENTED SANDS . . . . . . . . 6.1 INTRODUCTION

6.2 HOMOGENEOUS DRAINED BEHAVIOR

6.3 EFFECTS OF NONHOMOGENEITY ON CEMENTED SAND

6.4 VOLUME CHANGE BEHAVIOR

6.4.1 Volumetric Strain Characteristics

6.4.2 Effects of Cementation on Rate of Volume Change

6.4.3 Critical Void Ratio

. . . .

7.0 CYCLIC BEHAVIOR

7.1 INTRODUCTION

. . . . . . . . . . . . . . . . . . . . . . .

Table of Contents

29

32

35

40

45

45

45

45

47

50

50

50

54

62

62

63

74

77

77

78

84

92

92

vi

7.2 EFFECTS OF CEMENTATION ON LIQUEFACTION RESISTANCE 92

7. 3 EFFECT OF CEMENTATION ON DEVELOPMENT OF PORE PRESSURES AND STRAIN 96

7.4 EFFECT OF A WEAK LENS ON LIQUEFACTION RESISTANCE . . . . . 111

a.o SUMMARY and CONCLUSIONS

Appendix A. EQUIPMENT IDENTIFICATION . . . . . . . . . . . . . .

Appendix B. Use of the MTS cyclic Testing Apparatus . . . . . . B. 1 MTS Stress Controlled Cyclic Triaxial Testing Procedure

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . .

Vita . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Table of Contents

119

125

128

128

137

140

vii

LIST OF FIGURES

FIGURE PAGE

2-1 Cyclic Stress Ratio Versus Number of Cycles to 5% Double Amplitude Strain (after Rad And Clough, 1982) ................ 12

2-2 Normalized Plot of Pore Pressure Buildup in Cyclic Triaxial test on 1% Cemented Sand (after Rad and Clough, 1982) .•...... 14

3-1 Monterey #0/30 Grain Size Analysis ............................. 20

4-1 a) Sand Rainer and Mold Used for Cemented Sand Preparation. b) Disassembled Sand Rainer ..............•....•................ 31

4-2 Schematic of Trimmed Samples for Nonhomogeneous Sample Construction . ................................................ 3 7

4-3 Nonhomogeneous Sample Preparation Procedures ................... 38

4-4 Schematic of Vacuum Saturation Apparatus ......•................ 44

5-1 Schematic of Cyclic Testing Apparatus ...•...•.................. 52

5-2 Typical Results of a Cyclic Triaxial Compression Test .......... 55

5-3 Cyclic Shear Resistance Curve for Tamped, Monterey #0 Sand (after Silver, 1976) .........•.............•................. 57

5-4 Cyclic Shear Resistance Curve for Pluviated, Uncemented Sand ... 60

5-5 Peak Results from a Cyclic Triaxial Test on 2% Cemented Sand ... 61

6-1 Stress-Strain and Volume Change Plots for 2% Cemented Samples with Average Dry Density= 15.00 KN/M 3 •••••••••••••••••••••••• 64

6-2 Stress-Strain and Volume Change Plots for 2% Cemented Samples with Average Dry Density= 15.45 KN/M 3 •••••••••••••••••••••••• 65

6-3 Stress-Strain and Volume Change Plots for 2% Cemented Samples with Average Dry Density= 15. 70 KN/M 3 •••••••••••••••••••••••• 66

6-4 Peak Strength Envelopes for 2% Cemented Sand Samples with Average Dry Density= 15.00 KN/M 3 •••••••••••••••••••••••• 70

6-5 Peak Strength Envelopes for 2% Cemented Sand Samples with Average Dry Density= 15.45 KN/M 3 •••••••••••••••••••••••• 71

LIST OF FIGURES viii

6-6 Peak Strength Envelopes for 2% Cemented Sand Samples with Average Dry Density= 15. 70 KN/M 3 •••••••••••••••••••••••• 72

6-7 Stress-Strain and Volume Change Plots for Nonhomogeneously Cemented Sand . ............................................... 7 5

6-8 Peak Strength Envelopes for Nonhomogeneously Cemented Samples .. 76

6-9 Volume Strain at Failure Versus Initial Dry Unit Weight CD Triaxial Test (confining pressure= 103 KN/M2 ) •••••••••••• 79

6-10 Volume Strain at Failure Versus Initial Dry Unit Weight CD Triaxial Test (confining pressure= 207 KN/M 2 ) •••••••••••• 80

6-11 Volume Strain at Failure Versus Initial Dry Unit Weight CD Triaxial Test (confining pressure= 345 KN/M2 ) •••••••••••• 81

6·12 Dilation Angle Versus Initial Dry Unit Weight (Confining pressure = 103 KN/M2 ) ••••••••••••••••••••••••••••• 85

6-13 Dilation Angle Versus Initial Dry Unit Weight (Confining pressure = 207 KN/M2 ) ••••••••••••••••••••••••••••• 86

6-14 Dilation Angle Versus Initial Dry Unit Weight (Confining pressure = 345 KN/M2 ) ••••••••••••••••••••••••••••• 87

6-15 Volume Change at Failure Versus Initial Void Ratio ............. 89

6-16 Critical Void Ratio Versus Confining Pressure .................. 90

6-17 Critical Void Ratio Versus Confining Pressure for Cemented and Uncemented Monterey #0/30 Sand .....•..................... 91

7-1 Cyclic Shear Resistance Curves for Homogeneously Cemented Monterey fl0/30 Sands ......................................... 95

7-2 Pore Pressure Ratio Versus Cyclic Ratio ........................ 97

7-3 Pore Pressure Ratio Versus Cyclic Ratio (2% cemented sand) (after Rad and Clough, 1982) ................................. 99

7-4 Pore Pressure Ratio Versus Cyclic Ratio (uncemented sand) ..... 100

7-5 Pore Pressure Ratio Versus Cyclic Ratio (1% cemented sand) .... 101

7-6 Pore Pressure Ratio Versus Cyclic Ratio (2% cemented sand) .... 102

7-7 Strain Ratio Versus Cyclic Ratio (uncemented sand) ............ 105

7-8 Strain Ratio Versus Cyclic Ratio (1% cemented sand) ........... 106

LIST OF FIGURES ix

7-9 Strain Ratio Versus Cyclic Ratio (2% cemented sand) •.....•..•. 107

7-10 Pore Pressure Ratio Versus Cyclic Ratio Data Compared to Empirically Developed Curves ....•...•••..•...•....•....•.•.. 110

7-11 Cyclic Shear Resistance of Nonhomogeneously Cemented Sand Compared to Various Cementation Configurations .•..••.••••.•. 112

7-12 Unconfined Compressive Strength Versus Cyclic Stress Ratio to Cause Initial Liquefaciton ......•...••................... 116

7-13 Pore Pressure Ratio Versus Cyclic Ratio (nonhomogeneous) ..•.•• 117

7-14 Strain Ratio Versus Cyclic Ratio (nonhomogeneous) ....•........ 118

LIST OF FIGURES x

LIST OF TABLES

TABLE PAGE

2-1 Available Information on Cemented Sands ......................... 7

3-1 Comparison of Monterey #0/30 and Monterey #0 Index Propertes ... 21

3-2 Maximum and Minimum Index Void Ratios for Cemented Monterey #0/30 Sand from This Study and from Muzzy (1983) .... 24

3-3 Summary of Testing Program .•............•....•..•...•.......... 28

6-1 Sample Conditions and Test Results of CD Triaxial Tests on 2% Cemented Sand and Nonhomogeneous Samples .....•............... 67

6-2 Strength Parameters from CD Triaxial Tests on 2% Cemented Sand.73

7-1 Cyclic Triaxial Test Information ............................... 94

a-1 Equipment Information ......................................... 126

LIST OF TABLES xi

1.0 INTRODUCTION

The large amount of damage sustained in the Anchorage, Alaska and Niigata,

Japan earthquakes of 1964 brought to light the need to study earthquake

induced liquefaction of soils. During these and other earthquakes, pore

pressure buildup under undrained conditions resulted in reductions of

shear strength of the soil and led to a large percentage of the documented

failures. Soils most susceptible to liquefaction are medium to loose,

saturated sands in the 6 to 10 meter depth range.

Recent research has shown that small amounts of cementation in a sand

increase its ability to sustain static and dynamic loads, even in a

liquefaction type environment. This means that cementation has a sig-

nificant bearing on the likelyhood of liquefaction failure, and in some

cases might be used as a means to prevent failure. Previous studies have

examined the static and cyclic behavior of both naturally cemented mate-

rials and artificially prepared samples. The present work addresses three

of the questions as yet unanswered by other investigations:

1. What is the effect of nonhomogeneity on the liquefaction re-

sistance of weakly cemented sands?

2. How does cementation affect the volume change characteristics

of statically loaded samples?

INTRODUCTION 1

3. Is it possible to predict the pore pressure generation of un-

drained, weakly cemented sands subjected to cyclic loading?

In this research, a laboratory investigation was performed on arti-

ficially cemented samples of a standard sand. Samples created in this

fashion, by mixing various quantities of Portland cement with sand, have

been shown to appropriately model similar materials that are found in

nature. Initially, the testing program involved performing 14 static

triaxial compression tests on samples cemented with 2% cement, by weight,

and on nonhomogeneous, or layered, samples; performed to determine

strength, stiffness and volume change characteristics. Also, a series

of 26 stress controlled cyclic triaxial tests were performed to develop

cyclic strength curves and to observe the pore pressure generation char-

acteristics. Where possible, published test results were incorporated

to augment the present work.

To establish a basis for the results of this study, background information

is reviewed with regard to liquefaction and cementation in Chapter 2.

Chapter 3 outlines the experimental investigation, including the materi-

als and equipment used, and the testing procedures. Sample preparation

techniques as well as the procedure required to saturate the samples is

discussed in Chapter 4. A detailed description of the testing methods

and the equipment used is included in Chapter 5. The static behavior of

the cemented sands is presented in Chapter 6, and Chapter 7 discusses the

dynamic behavior. Chapter 8 provides a summary of the investigation and

the conclusions of this study.

INTRODUCTION 2

2.0 BACKGROUND

2.1 CEMENTED SOILS

Throughout the world, many natural sand deposits exhibit forms of bonding

between particles. The writer shall refer to this phenomenon as

cementation. One distinguishing characteristic of these materials is

that they are able to stand in steep slopes, approaching vertical. The

bonding, however, is often surprisingly weak, so that these materials can

be crumbled using finger pressure. The major focus of this work deals

with those sands that are only weakly cemented.

Cementation can be caused in nature by a number of different means:

• Welding of sand grains at their contact points. This can occur

due to the internal heat at deposition of such material as

volcanic ash. Prolonged pressure at contact points can also

lead to cold welding as described by Lee (1975).

• The presence of cementing agents. Various materials which are

created as byproducts of nearby weathering, or precipitated out

of groundwater can bond sand particles. These materials in-

clude clays, carbonates, silicates, and iron bearing materials.

BACKGROUND 3

Of particular interest to the present study is that the cementation of

sands is quite often nonhomogeneous. This is evident in e~~posed slopes

as a layering or banding. The resulting static and cyclic responses are

a function of two or more materials that exhibit different independent

behavior. Some of the phenomena that can cause nonhomogeneity include:

• Variable grain size distribution. This occurs in surface-water

borne deposits where seasonal fluctuations in flow can lead to

a vertical grading of grain sizes. The variations in surface

area and intergranular contact area of individual strata lead

to differing degrees of cementation.

• Variations in cementing agents. Inconsistent groundwater com-

position and fluctuation of the groundwater level can also lead

to nonhomogeneous cementation. This is accentuated by periodic

precipitation and leaching of the cementing agents.

2.2 CEMENTED SAND DEPOSITS

Cemented soils are widely distributed throughout the world. Some of the

more well known areas as cited by Rad and Clough (1982) are: along most

of the Pacific Coast in California and Oregon, where the common cementing

agents are carbonates, clays, and iron oxides; the deserts of the western

and southwestern United States, where precipitation of calcium carbonate

and other minerals results in a caliche-type soft rock (Hamel, 1973);

loess deposits of the midwestern United States and China (Close and

BACKGROUND 4

McCormick, 1922); large areas of central Guatemala, which are covered by

wind blown volcanic ash deposits (Harp and others, 1978; Sitar, 1979);

some parts of Japan (Yamanouchi and others, 1977) and North Island of New

Zealand (Yamanouchi, 1974), where pumice-flow deposits exist; the Kurkar

deposits along the Mediterranean coastline of Isreal and neighboring Arab

countries which are cemented mainly by calcereous cement (Frydman and

others, 1980); extensive areas of western and central Europe, where the

Keuper sandstone formation is found.

Recent studies have demonstrated that the strength contributions from low

levels of natural cementation are destroyed during sampling and subse-

quently missed in laboratory testing (Frydman et al. , 1980; Beckwith and

Hansen, 1981; Saxena and Lastrico, 1978; Clough and Bachus, 1982). This

suggests that it is possible that many sands are cemented, but not iden-

tified properly because of the disturbance factor in sampling.

2.3 STATIC BEHAVIOR OF WEAKLY CEMENTED SANDS

While there has been limited study of the behavior of cemented soils, the

researchers listed in Table 2-1 have identified important characteristics

of these materials. Some major findings from static tests on naturally

and artificially cemented sands and silts are as follows:

1. There are similarities between artificially and naturally ce-

mented sands.

BACKGROUND 5

2. The friction angle is similar to that of uncemented sands.

3. Cementation manifests itself as a cohesion intercept, with the

cohesion increasing with the level of cementation, amount of

fines, and particle angularity.

4. There is a small, but significant, tensile strength which typ-

ically is about 10% of the unconfined compressive strength.

5. The initial tangent modulus increases with confining pressure

and/or the level of cementation.

6. The brittleness of the sample increases by increasing the

cementation or decreasing the confining pressure.

7. Volumetric increases generally accompany shear failure even for

cemented sands with "loose structures". The volume changes

seem to occur more rapidly than they do in uncemented sands.

The available data base for cemented sands is very limited, particularly

for instances of negligible disturbance and controlled sample properties.

The present study augments work in this regard with a special emphasis

on the effects of nonhomogeneity in the soil, and further investigates

the volume change characteristics of these materials.

BACKGROUND 6

Table 2-la: Available information on cemented sand.

Soil Cementing Reference Tested Agent Sample Type Static Tests Dynamic Tests

Alfi* NCS C and C Hand Trimmed Drained Tx Non (1978)

Bachus et al.* NCS c and c Hand Trimmed (1981) ACS p c Compacted in Mold Drained Tx Non

Beckwith & Hansen NCS Carbonate Non Non Non (1981)

Clough et al.* NCS c and c Hand Trimmed (1981) ACS p c Compacted in Mold Drained Tx Non

Dupas and Pecker ACS p c Compacted in Mold Drained Tx Cyclic Tx (1979)

Frydman et al.** NCS ACS Hand Trimmed Non Cyclic Tx (1980)

Hamel NCS Carbonate Hand Trimmed Direct Shear Non (1973)

Mitchell ACS p c Compacted in Mold Indirect Tension Compression (1976) Flexure Repeated

Poulos NCS Carbonate Different Method Several Types Cyclic Tx (1980) Silicate

Reference

Rad & Clough* (1982)

Salamone et al. (1978)

Saxena & Lastrico (1978)

Sitar* (1979)

Sitar and Clough* (1979)

Sitar et al.* (1980)

Yamanouchi et al. (1977)

00

Table 2-lb: Available information on cemented sand (continued).

Soil Cementing Tested Agent

NCS c and c ACS PC

NCS Carbonate

NCS Carbonate

NCS c and c ACS p c

NCS c and c ACS p c

NCS c and c ACS p c

NCS Thermal Welding

Sample Type

Hand Trimmed Pluviated

76 mm Dension sampler

76 mm Dension sampler

Hand Trimmed Compacted in Mold



Shirasu Cutter (5 cm dia. tubes)

* Similar Research ** Some insitu tests

Static Tests

Drained Tx

Undrained Tx

Undrained Tx

Drained Tx

Drained Tx

Drained Tx

Several Types

NCS Naturally Cemented Sands ACS = Artificially Cemented Sands Tx Triaxial Test C and C= Carbonate and Clay P C Portland Cement

Dynamic Tests

Cyclic Tx

Cyclic Tx

Non

Simple Shear Cyclic Tx



Non

2,4 LIQUEFACTION

Liquefaction is described by Youd ( 1972) as, "the transformation of a

granular material from a solid into a liquid state as a consequence of

increased pore water pressures." It develops as a consequence of the

propagation of shear stresses due to seismic events, through the soil,

resulting in shear strains in the sand. If the soil is a saturated sand,

and behaves in an undrained mode, the tendency of the soil to strain under

the shear stresses will result in the development of excess pore pres-

sures. The generated pore pressures can be high enough to lower the ef-

fective confining stresses to zero, resulting in drastic strength losses

and possible large strain development, particularly in loose deposits.

This phenomenon has led to catastrophic slope and foundation failures in

recent history.

Conventionally, the term "liquefaction" has several definitations:

• "initial liquefaction" is defined as the point when excess pore

pressures are first equal to the effective confining pressures

that existed just prior to loading.

• Liquefaction can also describe a condition of some predeter-

mined amount of strain, often 5% or 10% for research purposes.

BACKGROUND 9

The reader is referred to The Committee on Soil Dynamics (1978) for a more

complete discussion of related terms. Unless otherwise stated, this re-

port uses the term liquefaction as it relates to initial liquefaction.

Since the mid 1960' s, when liquefaction was recognized as a potential

hazard, a number of methods have been designed for predicting the like-

lihood of its occurrence. These have been important and useful contrib-

utions in light of the heavy development of known seismic areas. At the

present, however, the accepted methods do not directly account for

cementation, which is generally neglected as a conservative assumption;

rather, their influence enters design correlations when they are present

in the field data used as the basis for these methods.

2.5 CYCLIC BEHAVIOR OF WEAKLY CEMENTED SAND

The available data for the cyclic behavior of cemented sands suggests that

cementation increases the cyclic shear resistance of uncemented, but

otherwise similar, sands. This means that cemented sands are better able

to withstand the effects of dynamic loading than are uncemented sands.

It has also been observed that increased levels of cementation will result

in even greater resistance to liquefaction.

In nature, soils may exhibit progressively increased levels of

cementation as a function of age. Lee (1975) has proposed that, even in

the absence of cementing agents, sand particles can become "cold welded"

as a result of prolonged contact under pressure. To simulate these older,

BACKGROUND 10

cemented materials in the laboratory within a reasonable time span, rel·

atively small amounts of cementing agents, often in the form of Portland

cement, are added to sand samples. In fact, while investigating the dy-

namic properties of artificially cemented sands, Dupas and Pecker (1979)

found that cement quantities in excess of 5% of the dry weight of sand

were enough to make the sand totally resistant to liquefaction.

In a study of a weakly cemented natural beach sand, Rad and Clough (1982)

observed that this material required very high stress levels to cause

liquefaction. These researchers also conducted a program of tests on

weakly cemented, artificially prepared sand. They were able to establish

a correlation between level of cementation and liquefaction resistance

for homogeneous cemented sand. This is demonstrated in Figure 2-1 which

plots cyclic shear stress ratio versus the number of cycles to cause 5%

double amplitude axial strain. It is seen here that samples containing

higher levels of cementation require higher stress levels to induce this

amount of strain at the same number of cycles.

Weakly cemented zones within a more strongly cemented sand mass were noted

to lower the liquefaction resistance of a sand (Frydman, et al., 1980).

Clear trends for this effect could not be quantified, however, due to the

variability of the natural materials studied. The present work examines

this issue, using artificially created samples with controlled nonhomo-

geneity.

BACKGROUND 11

~ ~

~ < ~

<J) 00 UJ ~ ~ ~

~ < w :I: ~

u ~

_J u r u

0.6

% CEMENT 0.4

0.2

0.0 10

NUMBER 0F STRESS CYCLES, N

Figure 2-1: Cyclic stress ratio versus the number of cycles to cause 5% double amplitude strain (after Rad and Clough, 1982).

BACKGROUND 12

Rad and Clough (1982) observed that pore pressure development patterns

of cemented sands snbjected to dynamic loading are different than those

of uncemented sands. This is shown in Figure 2-2 which is discussed in

detail in Chapter 7. Basically, this figure is a normalized plot of pore

pressure versus load cycle for cyclic triaxial tests. It can be seen that

the data points for cemented sand fall outside the shaded zone repres-

enting the observed behavior of uncemented sands (Lee and Albeisa, 1975).

Although empirical relationships exist for predicting pore pressure gen-

eration in uncemented sands they appear inappropriate for cemented sands.

The present investigation carries this work further.

2.6 SUMMARY

Weakly cemented sands are found in many parts of the world. They are able

to stand in very steep slopes, but can fail catastrophically when sub-

jected to dynamic loads. The cementation of natural sand deposits is

sometimes nonhomogeneous, containing interbedded strata or isolated

pockets of material that is less cemented than the surrounding mass.

Sample disturbance effects have made it difficult both to identify ce-

mented soils in the field and to characterize them in the laboratory.

Static testing on naturally and artificially cemented sands has shown them

to exhibit a similar frictional response to uncemented sands, while having

a cohesion intercept and stiffer behavior. Field evidence suggests that

cemented sands can be quite resistance to liquefaction. This is sub-

stantiated by cyclic testing of these materials which shows the cemented

BACKGROUND 13

1.0 .. • • • • • • lbu • • • ' 0.8 :::> I :::l ... • • • .. • CS> 0.5 • -~

< a:: • w • a:: ::> 0.4 • (/) (/) • w a:: 0.. w Lee and Albeisa a:: 0.2 (Observed range for CS> uncemented sand) a...

1% CEMENT 0.0

0 0.2 0.4 0.6 0.8

CYCLIC RA TI0,

Figure 2-2: Normalized plot of pore pressure buildup in cyclic triaxial tests on 1% cemented sand (after Rad and Clough, 1982).

1

BACKGROUND 14

sands to be more resistant to seismic loads than uncemented sands, with·

greater differences at higher levels of cementation.

The limited amount of available data needs to be supported in the areas

of: the effects of weak layers on the dynamic behavior of stronger

masses; the effects of cementation on the volume change characteristics

of statically loaded samples; quantifying the behavior of cemented soils

under undrained cyclic loads.

BACKGROUND 15

3.0 EXPERIMENTAL INVESTIGATION

3.1 INTRODUCTION

The major objectives of this testing program are to investigate:

1. the effects of a weak layer on the static and cyclic behavior

of a more strongly cemented mass;

2. the volume change behavior of cemented sands during static

loading;

3. the pore pressure generation characteristics of cemented sands,

subjected to cyclic loads.

Due to difficulties in obtaining undisturbed samples of cemented sand,

artificial samples were used exclusively for this investigation. This

chapter describes the use of artificial samples and the materials used

in their creation. Also included are outlines of the sample preparation

techniques used and the laboratory test program undertaken which includes

index testing as well as static and cyclic triaxial testing.

EXPERIMENTAL INVESTIGATION 16

3.2 ARTIFICIALLY PREPARED SAMPLES

The process of sampling naturally cemented sand deposits by conventional

means, such as driven samplers, often disturbs or destroys the

cementation. Thus, to examine the influences of cementation in the lab-

oratory, it is usually necessary to retrieve undisturbed samples by a time

consuming and difficult hand sampling method. Even with careful attention

to preserving the in-situ qualities of cemented sands, intrasample dis-

continuities and nonuniform cementation as well as variations between

samples are likely to exist. Even a well performed laboratory investi-

gation with such samples can lead to test results that are difficult to

interpret, exhibiting apparently anomalous behavior, as exhibited by

Saxena and Lastrico (1978).

It has been shown (Sitar (1979), Rad and Clough (1982)) that artificially

prepared and cemented samples acceptablly model the behavior of naturally

cemented materials by responding similarly to changes in test controls.

The great benefit of this is that samples with carefully controlled

cementation and density are readily available for laboratory testing.

Samples were created for this investigation with 1 and 2 percent Portland

Type I cement, by weight, at average densities of 15.00, 15.45, and 15.70

KN/M 3 • No higher values were used because stronger and denser samples

are simply not liquefiable under most conditions. The average densities

chosen are consistent with those of previous investigations by Rad and

Clough (1982). Sample preparation is discussed in-depth in Chapter 4.


Basically, a sand-cement mix is rained into molds. The samples are then

saturated by allowing water to slowly petcolate up into the mold through

porous bottom plates. Finally, after a minimum initial curing period of

one day, the samples are transferred to a humid room for additional cur-

ing.

The homogeneous samples were allowed to cure for a total of 14 days in

the saturated environment. This allowed for about a two day window of

possible testing dates with samples of similar strengths after curing.

Nonhomogeneous samples were created by layering partially cured samples

of differing cement contents. Additional information on this procedure

is provided in Chapter 4.

3.3 MATERIALS USED

Monterey #0/30 beach sand was used exclusively for the testing program.

This washed and sieved sand, produced by Lone Star Industries, San Mateo,

California, is predominantly subangular to subrounded quartz silica with

some feldspar. This material, as well as the similar Monterey #0 sand,

is commonly used in investigations of liquefaction problems. A grain size

analysis was performed on the Monterey #0/30 and is presented in Figure

3-1. Since it compares quite closely with that shown by Muzzy (1983),

the minimum and maximum void ratios developed in his study are compared

to values developed by Silver (1976) for Monterey #0 sand (Table 3-1).

A preliminary analysis, described later in this chapter, was performed

during the present investigation and resulted in possible discrepancies


with the values proposed by Muzzy and subsequently discussed by the

American Society of Testing and Materials (ASTM) D18.09.02C Task Group.

The cementing agent used was Portland Type I cement, also produced by Lone

Star Industries. It is relatively easy to use and quantify, and can

provide consistent results. Similar material has been used in previous

studies of artificially cemented sands. The cement was stored in moisture

tight containers while awaiting use to inhibit hydration.

3.4 INDEX TESTING

The maximum and minimum void ratios for uncemented Monterey #0/30 sand

have been determined by Muzzy (1983) as presented in Section 3.3. How-

ever, the characteristics of the sand-cement matrix alter as cement

crystals develop during hydration. To generate index values for the ce-

mented sands, tests were performed following a 14 day curing period so

that the materials would be similar to those used for static and cyclic

testing. As a reference, maximum and minimum index void ratios were also

developed for the uncemented sand.

Sand-cement mixes of 1% and 2% cement content, by weight, were prepared

in molds (as discussed in Chapter 4) and cured in a saturated environment

for 14 days. The samples were then extruded, hand crumbled to individual

particles, and oven dried to cease hydration. The resulting material


trl :><: "'d trl ~ H

~

~ t"'i H

~ C/l t-3 H Ci1

~ H 0 z

N 0

I-:r: (!)

w 3:

>-al

0:::: w z LL

I-z w 0 a::: w Q_

100

90

80

70

60

50

40

30

20

10

0

Gravel Coarse

3"

-

-

-

-

-

"""""

,_

-

,_

I I I I I 0 0 0 0 CXl \0

1.511

I 0 v

I

Sand Fine Coarse Medium Fine

U.S. STANDARD SIEVE SIZE 3 II 3 II /'4 :Is 4

I 0 C\J

II I I I I I

Q CXl \0 v

GRAIN

10 21) 30 40 60 100

~

)

I I 11 I I ;\ "\...J ,,.~

C\J C\J 0

SIZE IN MILLIMETERS

Fines Silt

200

11 I I I I I -: CXl \0 ooq

ci 0

v 0 0

Figure 3-1: Monterey #0/30 grain size analysis.

I C\J 0 0

-

-

-

-

-

-

-

-

-

q 0

100

90

80 I-:r:

70 (!) jjJ 3:

60 >-Cl'.I

50 0:::: w z LL

40 I-z w

30 0 a::: w Q_

20

10

0

Table 3-1: Comparison of Monterey #0/30 and Monterey #0 index properties.

SAND MONTEREY #0 MONTEREY #0/30

STUDY SILVER MUZZY THIS (1976) ( 1983) STUDY

Gs 2.65 2.65 2.65

yd-max 105. 7 105.8 -

Yd-min 89.3 91. 7 -

emax 0.852 0.803 -

emin 0.564 0.563 -

D50 0.36 0.45 0.45

cu 1. 50 1. 60 1. 37

Cc 0.90 1. 00 0.95


exhibited little free cement, suggesting that it was comprised of a mass

of individual sand grains that were coated, in part, with cement crystals.

3.4.1 Specific Grayitv

Specific gravity determinations were performed on each of the cemented

as well as the uncemented sand, as per ASTM D854. All three materials

showed specific gravities equal to 2.65. This is the same value reported

by Silver (1976) for Monterey #0 and by Muzzy (1983) for Monterey #0/30

sand.

3.4.2 Maximum Index Void Ratio

The maximum void ratios were determined using Method C of the ASTM

D4254-83 Minimum Index Density Test. This test comprises inverting a

stoppered cylinder, partially filled with a known amount of sand, then

tilting it back to the original vertical position. The minimum index

density (maximum index void ratio) is calculated from the resulting

measured volume. The cylinder in this study differs slightly from that

suggested by ASTM. The specification calls for a 2000 ml cylinder about

3 inches in diameter. The actual cylinder used is 3.25 inches in diameter

with a volume of 3153 ml. The height difference between the cylinders

which is a major controlling parameter is 15 cm, or about 30%. This

discrepancy is considered acceptable given that the intent of these tests

is simply to give insight to the sensitivity of maximum index void ratio

to cementation.


The raining apparatus used to create samples for this investigation, and

discussed in ChP.pter 4, can be fitted with a variety of raining plates

that control the density of the constructed samples. To obtain a second

value for comparison, the rainer was fitted with the plate that was

available to produce the loosest possible samples. Sand was rained into

a cylinder of known volume after which the weight was calculated to de-

termine the maximum index void ratio.

The maximum void ratios as determined from both methods are presented in

Table 3.2. These results demonstrate that cementation leads to higher

maximum void ratios. Note that for the uncemented sand, the ASTM method

used in this investigation produced a maximum void ratio in excess of that

reported by Muzzy (1983). Since ASTM procedure was not strictly adhered

to, the higher value may not be accurate. Nevertheless, it would seem

that this void ratio is closer to the 'true' maximum since the ASTM pro-

cedure probably allows for a smaller range of variability than is seen

with these two studies. In light of the similarity between the grain size

properties of Monterey #0 and #0/30, it would also seem that the maximum

void ratios for the two materials should be rather close, as indicated

by the present study.

3.4.3 Minimum Index Void Ratio

The method used to develop minimum index void ratios for the three mate-

rials uses the rainer mentioned previously. In this case the rainer was

fixed with a plate having small holes, resulting in dense packing. The


Table 3-2: Maximum and minumum index void ratios for cemented Monterey #0/30 sand from this study and from Muzzy ( 1983).

MAXIMUM VOID RATIO MINIMUM VOID RATIO CEMENT CONTENT

Muzzy 'ASTM' rainer Muzzy rainer

0% . 803 . 884 . 748 . 563 . 555

1% - . 953 . 852 - . 625

2% - 1. 102 . 903 - . 658


vibratory table recommended by ASTM D4253-83 was not available to the

investigator. Similar apparati were no~ acquired or fabricated because

it was felt that such agitation could disturb the cemented sands by

freeing cement crystals from the sand grains.

The minimum index void ratio data are included in Table 3-2. Again, it

is apparent that increased cementation leads to looser packing as evi-

denced by increasing minimum void ratios. This is the same observation

made from the maximum void ratio data. The minimum value determined for

the uncemented sand by this method is relatively close to but, neverthe-

less, lower than that reported by Muzzy (1983).

3.4.4 Use of Index properties

It is evident from the observed results that there would be problems en-

countered when applying uncemented sand index properties to cemented

sands. It should be pointed out that this observation may only apply to

cemented sands in which cement crystals are present as opposed to cold

welded soils. Relative density calculations based on uncemented index

properties would result in erroneously high values. In any case, the

exact meaning of relative density for cemented sands is not clear since

there are structural differences between the cemented and uncemented

sands. It would seem somewhat confusing to refer to the relative density

of cemented sands as specifically related to uncemented sand properties.

Rather, in the writer's opinion, in order to isolate the structural

characteristics of cementation from index values of the sand samples, it


is preferable to use dry unit weight to distinguish density. Such prac-

tice has been adopted for this report. When applicable, relative densi-

ties reported by other researchers have been converted to dry unit

weights, using index properties provided by the respective researchers.

3.5 STATIC TESTS

It is difficult to meaningfully quantify cementation, due to the great

variety of possible cementing agents. To measure cementation as a percent

of dry weight of the host sand has different meaning for various cementing

agents. Therefore, it is more useful to quantify the effects of

cementation in terms of static strength rather than percent cement in the

soil. To this end, and to investigate the applicability of the critical

void ratio concept to cemented sands, a static testing program was per-

formed. A family of consolidated, drained, triaxial compression tests

was executed on each of the homogeneous materials and on the layered

samples. The procedures followed the general guidelines presented by

Bishop and Henkel (1962). Volume change during the tests was measured

by means of a calibrated burrette in series with sample drainage lines.

A number of unconfined compression tests were also performed on the 2

percent cemented material to observe the sensitivity of the unconfined

compressive strength to testing procedure.

An early concern was that consolidation strains would disrupt the

cementation of samples prior to actual axial loading. Indeed, this pos-

sibility was investigated by Rad and Clough (1982) and found to be non-


existent. Along these lines, however, the writer was curious about the

behavior of samples in which the cementation had been disturbed before

testing. In order to observe the extreme case, a 2% cemented and cured

sample was oven dried and subsequently crumbled by hand. The resulting

sand grains were reconstituted to a similar density as used for the ce-

mented sands, and subjected to drained triaxial compression.

Table 3-3 presents sample and test information for the static testing

program.

3.6 CYCLIC TESTS

Undrained cyclic triaxial tests were performed on uncemented and cemented

samples, using the standard test procedure described by Silver (1976).

A minimum of three tests, at different stress ratios, were performed on

each of the different cemented and uncemented materials to develop the

cyclic shear resistance curves, and to observe the pore pressure gener-

ation behavior of these materials. Table 3-3 includes the numbers of

tests for each catagory of material. 6 cyclic tests were performed on

tamped samples during the development of the testing procedure; a total

of 19 cyclic triaxial tests were subsequently performed on pluviated

samples.


Table 3-3: Summary of testing program.

SAMPLE NUMBER OF NUMBER OF NUMBER OF TYPE, STATIC CYCLIC UNCONFINED

CEMENTATION TESTS TESTS TESTS

0% tamped - 7 -0% pluviated - 4 -

1% - 6 -2% 11 3 2

layered 3 6 -2% crumbled 1 - -


4.0 SAMPLE PREPARATION

4.1 USE OF THE RAINER

The process of preparing a sample by letting sand fall, through air or

liquid, into the sample mold is called pluviation. Pluviation allows a

sample to be prepared in an efficient manner to an established density

with relatively homogeneous properties. Mulilis et al. (1979) describe

the procedure and conclude it is preferable to other methods for research

studies. Rad and Clough (1982) used this procedure for their investi-

gation into the behavior of cemented sands.

In this investigation, an effort was undertaken to optimize the pluviation

technique with regard to simplicity, repeatability, sample homogeneity,

and density control. After attempting a number of different techniques,

a raining method proved the most convenient; whereby the sand-cement mix

is poured through a porous plate at a fixed height above the sample.

Unfortunately, while homogeneous uncemented sand samples could be ob-

tained this way, this was not the case in the initial trials with the

cemented sands.

To check the first samples constructed by this method, they were cured,

air dried and trimmed along both horizontal and vertical planes. The

exposed soil showed vertical columns of darker colored and higher strength

material in locations corresponding to the holes in the rainer plate.

SAMPLE PREPARATION 29

Obviously, the cement had segregated, probably due to different raining

characteristics of the sand and cement, and to the mechanics of imFact

at the rising sample surface. Fortunately, this undesirable effect was

found to be eliminated by adding a diffusing screen approximately 10 mm

below the porous rainer plate. The diffusing screen served to maintain

the sand and cement in a mixture in the completed samples. A number of

samples prepared by the improved technique were inspected by the process

described previously. These samples appeared to have uniform distrib-

ution of cement with no visible color or strength variation.

The sample preparation technique that was finally adopted utilizes a

specially constructed sand rainer (Eid, 1984) that is shown in Figure 4-1.

Two adapter bushings were fabricated for the original rainer, which allow

it to mate with the sample molds and provide a constant cross section

during free fall of the sand-cement mix. Besides allowing for density

control with the use of changeable rainer and diffuser plates, this device

affords homogeneous, consistent, and repeatable sample preparation.


Figure 4-la: Sand rainer and mold used for cemented sand preparation.

Figure 4-lb: Disassembled sand rainer.


4,2 HOMOGENEOUS SAMPLES

All samples were prepared in the laboratory using Monterey #0/30 sand and

Portland Type I cement. It was necessary to first moisten the sand

slightly to insure that the cement was completely and evenly distributed

during mixing. The moisture was kept to 0.35%, by weight, to prevent the

mix from bulking up on the diffuser screen during raining. This quantity

of water was found sufficient to insure that all of the cement was dis-

tributed and bound to the sand grains by capillary tension. After mixing

the moistened sand with the appropriate amount of cement, the mixture was

poured through the rainer into the cylindrical mold shown, both of which

are shown in Figure 4-la. The molds were fabricated from plexiglass

tubing with an inside diameter of approximately 71 mm, cut to a length

of 178 mm with a single longitudinal split. A circular, aluminum plate

with five small diameter drainage holes was fitted to the bottom of the

cylinder which was subsequently secured with two hose clamps. Prior to

preparing the samples, the molds were sprayed with silicon lubricant and

a disk of filter paper was placed in the bottom of each. The sand rainer

was then used to create the samples, with densities being controlled with

properly chosen rainer plate and diffuser screen combinations. The sam-

ples were saturated by allowing the water level to slowly rise through

the porous plate on the bottom of the molds, which had been set on a

pervious bed in a styrofoam box.

The procedure used to prepare the homogeneous samples is as follows:


1. Rainer is assembled with correct porous plate and diffuser

screen combination which is experimentally determined to result

in samples of the desired dry unit weight (relative density).

2. Inside surface of assembled mold is coated with thin coat of

silicon lubricant; filter pa.per is set into bottom of mold.

3. A course sand bed, a.bout 2 centimeters thick, is placed a.t the

bottom of the saturation box to allow free flow of water into

samples. The box is placed a.t a. water source to minimize the

number of times the uncured samples need to be relocated.

4. 1500 grams of a.ir dried sand a.re weighed into mixing bowl.

5. Appropriate a.mount of cement is weighed into a. sepera.te bowl;

this corresponds to 15 grams for the 1 percent mix and 30 grams

for the 2 percent mix. Cement clumps a.re broken up and cement

is discarded if it seems to have begun hydra.ting.

6. 5.2 cc of water (approximately 0.35% of dry weight of sand) is

added to sand which is then mixed thoroughly for a.t lea.st one

minute with spatula. or electric mixer. The same a.mount of

moisture is used for a.11 tests a.s it is a controlling factor

in resultant dry unit weight.


7. Cement is slowly added to moistened sand while it is being

stirred, and mixing is then continued for at least one minute

with spatula or electric mixer.

8. Sand-cement mix is transferred to flask.

9. Rainer is placed on mold and sand is poured through at a con-

stant rate, maintaining a constant 15 to 25 mm head of sand

above the top porous plate. Sand should be added to the mold

until the level rises at least 20 mm above the top of the mold.

Rainer is removed with a vertical motion without disturbance

to mold and excess sand is gently stricken from top of mold.

10. Full mold is transferred to saturation box and slow flow of

water into box is begun, allowing water level to rise through

sample at a rate of approximately 8 centimeters per hour.

11. A small settlement, of approximately 2 mm, may occur at the top

due to the breakdown of capillary tension and particle rear-

rangement.

12. After sample has been allowed to cure in place for at lease 24

hours, it is transferred in saturation box to humid room for

remainder of curing period. The initial curing period helps

to minimize sample densification during transport from the

fabrication area.


13. After 14 days, the top and bottom few centimeters of the sample

are trimmed as a precaution against high cement concentrations.

This is done by prying open the longitudinal split and sliding

the sample to use the mold ends as trimming guides. The sample

is then placed on the triaxial cell bottom platen and filter

paper which have been previously deaired as an aid to sample

saturation. The mold should be.used to provide support to the

sample until it is resting securely on the bottom platen of the

triaxial cell.

Note: It is prudent to prepare at least one spare sample for every

one to two samples that are intended for testing on the same day.

4.3 NONHOMOGENEOUS SAMPLES

A number of different methods were considered for preparing samples to

test the effects of weaker layers of cemented sand within a more strongly

cemented mass. The method adopted and described herein uses cured mate-

rials that are virtually identical to the homogeneous samples. It allows

for control of the relative levels of cementation and the thickness of

the weak layer.

Homogeneous samples of 1 and 2 percent cemented sands that were cured for

seven days are trimmed as shown schematically in Figure 4-2 and layered

to create a nonhomogeneous sample. The newly assembled sample is returned

to a saturated environment for the remainder of the curing period.


The method used is demonstrated in the following photographs, and procedes

as follows:

1. A small batch of 2 percent sand-cement mix is prepared as de-

scribed in the homogeneous sample procedure.

2. 1 and 2 percent samples which have cured for seven days, are

trimmed to the required lengths as shown in Figure 4-2. Samples

should remain confined for the trimming process, and guides

should be used to insure square ends. (A plexiglass sample mold

was trimmed to a variety of lengths to serve both purposes.)

3. After setting the bottom layer vertically (onto a mold end

plate), its top surface is coated with a thin layer of the

sand-cement mix and the central layer is placed upon it. This

procedure is repeated for the top layer.

4. Mold is pried open and carefully lowered around sandwiched

sample until it bears on the edges of the bottom plate. Mold

is secured with hose clamps.

5. Sample is slowly submerged into water bath to cure for an ad-

ditional seven days.


'"'d ~ '"'d s H 0 z

I 0/o

Homogeneous, 1°/o and 2 °/o cemented samples, cured for 7 days.

o• I I

o• Samples are trimmed to proper lengths and ends are made square. Top and bottom few centimeters of 2°/o sample are discarded.

Coot w/ 2°/o mix

D Ends are coated with fresh 2% cement mix as layers are stacked.

T 7cm

_J_ 4m_ 7cm

_L

Layered sample is cured in mold for 7 additional days.

Figure 4-2: Schematic of trimmed samples for nonhomogeneous sample construction.

Figure 4-3a: Bottom layer of 2% sample is trimmed from entire sample, using guide.

Figure 4-3b: Bottom layer is treated with 2% cemented mix.

Figure 4-3c: 1% section, trimmed on bottom, is put in place. Mold is then removed.


Figure 4-3d: Weak layer is trimmed to desired thickness, using guide, and subsequently treated with 2% mix.

Figure 4-3e: Upper 2% section, which was previously trimmed on bottom, is put in place.

Figure4-3f: Mold is pried open, moved to contact bottom platen, and secured with hose clamps.


4.4 SATURATION

To properly measure the volume change behavior and pore pressure gener-

ation of these materials while subjected to static and cyclic loading,

it is essential that they are saturated. In order to saturate a sample,

the voids are filled with deaired water while any entrapped air is usually

driven into solution using increased backpressures (Lowe and Johnson

(1960)). The criteria developed by Skempton (1954) is typically used to

determine the degree of saturation. Herein, the ratio of induced pore

pressure to increased confining pressure, or Skempton's B-parameter, is

monitored between incremental backpressure increases. Ratios in excess

of 0.95 generally indicate a noncompressible pore structure, correspond-

ing to saturated conditions.

With clean sands it is often helpful to percolate the sample with carbon

dioxide prior to flushing with deaired water. The carbon dioxide dis-

solves in water more easily than does air during backpressure saturation

leading to lower backpressures required for complete saturation. This

procedure was considered undesirable for the cemented sands, however, due

to the likelyhood of a deleterious chemical reaction between the carbon

dioxide and the cement.

Due to the presence of cement crystals and to the increased sample

stiffness, it was noticed that high backpressures are required to saturate

the cemented materials. A vacuum saturation technique, described by Rad

and Clough (1984), was developed to mitigate this effect. The reader is


referred to this paper for the theoretical background and experimental

ver:f.fication of the procedure. The apparatus used for the present re-

search is shown schematically in Figure 4-4. The following procedure

represents a slight modifications of the original technique, because the

present apparatus allows for simpler setting and monitoring of the initial

effective confining vacuum, and affords more accurate determination of

the consolidated sample volume for density calculations.

The procedure is as follows:

1. Set sample in membrane onto triaxial cell with valves Tl and

T2 closed, and valves T3 and T4 opened to the flushing tanks.

2. Set regulator R2 to zero. Apply vacuum to regulator Rl which

is then set to 14 KN/M2 ( 4 inches Hg as read on mercury

manometer). Open valve T2 to top of sample, which applies a

negative backpressure condition.

3. Measure the height of the sample at four locations and measure

the diameter at three locations with a pi-tape.

4. Secure outer cylinder on triaxial cell and fill with water,

leaving at least 1 inch air space at top of cell. (Insure that

cell is vented during the filling process. ) Connect vacuum from

R2 to top of cell.


S. Increase total vacuum at Rl at an increment of about 14 KN/M2 ,

adjusting R2 simultaneously to maintain 14 KN/M2 (4 inches Hg)

14 KN/M2 effective confinment. When air seems to have stopped

flowing from top of sample, increase vacuum at Rl again. Repeat

this procedure until maximum available vacuum is achieved.

6. Open valve Tl, allowing flow of desired water through sample

from upper flushing tank. This water must be desired just prior

to sample saturation as flushing tank is not airtight.

7. When sample appears saturated and bubbles have stopped flowing,

close valve Tl and reduce vacuum at valve Rl to the initial

total vacuum, while simultaneously adjusting regulator R2 until

it is zeroed. Open valve Tl.

8. Remove vacuum line from cell and replace it with cell pressure

line. Connect a low pressure guage to monitor cell pressure.

9. Simultaneously increase cell pressure and reduce vacuum, main-

taining effective confinement, until vacuum is completely re-

placed with cell pressure.

10. Backpressure saturate sample while checking Skempton's B-

parameter.


B values in excess of 0.96 were achieved for all tests, at backpressures

on the order of 350 KN/M2 •


AIR COMPRESSOR

VACUUM PUMP

AIR COMPRESSOR

l

.. : : ...

·:· .· : .

TRIAXIAL CELL

UPPER FLUSHING TANK

a:: UJ 0 0 <( ....J CD

a:: <(

R2i-----------------------

MERCURY MANOMETER

LOWER FLUSHING TANK

Figure 4-4: Schematic of vacuum saturation apparatus.


S.O TEST PROGRAM, METHODS, AND EQUIPMENT

S.1 INTRODUCTION

This chapter discusses the testing program undertaken for this thesis,

which can be divided into three distinct phases. The first involves ma-

terial identification and index testing, as described in Chapter 3. The

two other aspects concern static and cyclic testing. The work was per-

formed both to augment previous efforts and to expand the understanding

of the behavior of weakly cemented sands in seismic environments.

S.2 STATIC TESTING

S.2.1 Introduction

Chapter 3 outlines the known research dealing with the static behavior

of lightly cemented sands. Most of the work in this area is concerned

with natural soils; materials which generally exhibit an appreciable de-

gree of variability. The properties of artificially created samples,

however, can be controlled in the laboratory. The effects of cementation

on static behavior can thus be more accurately isolated and quantified

if prepared samples are used.

Rad and Clough (1982) have done extensive static testing on artificially

prepared samples of cemented sand, and have documented many of their

TEST PROGRAM, METHODS, AND EQUIPMENT 45

specific characteristics. Their testing procedures were used as a general

guideline for the present study; their data were also used where possible

for comparative purposes and to enlarge the available data base for this

investigation.

The major portion of the static testing program involved 11 strain con-

t,rolled, consolidated, drained, cyclic triaxial tests on 2% cemented

samples, by weight, as well as similar tests on 3 layered, or nonhomoge-

neous, samples. Two unconfined compression tests were also performed on

the 2% cemented sand. Finally, one consolidated, drained triaxial test

was performed on a sample of the 2% cemented material that was cured,

crumbled, and subsequently reconstituted prior to testing. Of interest

here was the difference in strength and volume change behavior between

the crumbled sample and those which were intact prior to loading.

The intent of the test program on the 2% material was to develop strength

parameters, and observe volume change behavior. The strengths are im-

portant both as a measure of cementation and as a basis of comparison for

the effects of a weak lens on the static behavior of a stronger mass.

Volume change behavior is of interest as it relates to liquefaction re-

sistance. The nonhomogeneous samples were tested in static compression

to determine whether a reduction in liquefaction resistance, owing to the

presence of a weak lens, would be evident in static behavior.


S.2.2 Consolidated Drained Triaxial Testing and Equipment

Both the homogeneous and layered samples were tested in an identical

manner, and using the same equipment. The single crumbled and reconsti-

tuted sample was also subjected to this type of loading. Following sample

preparation and curing, which is described in Chapter 4, 7 cm diameter

samples were trimmed to approximately 15.3 cm in length and placed on the

triaxial cell. The triaxial cell and pressure/volume change panel was

purchased from Geotechnical Equipment Corporation in Highland Park,

Illinois. Latex membranes with a wall thickness of approximately 0.3 mm

were used to isolate the samples from the cell pressures. The top and

bottom platens are flush fit with porous brass material to allow free

drainage. A disk of Whatman #1 filter paper was placed at each end of

the sample to minimize transport of cement through the drainage lines.

The drainage lines consist of rigid Saran tubing with a wall thickness

of about 0.6 mm, providing for a drainage system with negligible flexi-

bility.

With a 4 inch mercury vacuum applied to the sample, the height was meas-

ured at four locations with a scale accurate to 0.4 mm. The diameter was

measured at the one-third points with a pi-tape accurate to 0.03 mm. The

triaxial chamber was then assembled around the sample and filled with

water, following which the sample vacuum was replaced with an equivalent

cell pressure.


Sample saturation, as discussed in Chapter 4, requires that cell pressure

and backpressure be monitored in order to check Skempton's B-parameter.

This was done with Entran pressure transducers that were calibrated prior

to the start of this test program. One transducer was connected directly

to the triaxial chamber and the other was connected to both the top and

bottom sample drainage lines by means of a t-fitting.

Samples were consolidated once the B-parameter was found to be in excess

of 0.96, whence the samples were assumed to be saturated. Volume change

during both consolidation and axial compression was calculated by meas-

uring the amount of water expelled from or drawn into the sample. This

was done with a graduated burette, calibrated to 1.325 cc per centimeter

of height, that was connected directly to the drainage lines. A burette

with a 55 cc capacity was found necessary to accommodate the volumetric

expansion of the cemented samples. Consolidation was generally allowed

to continue for about thirty minutes before the samples were axially

loaded. Each of the samples was trimmed, saturated, consolidated, and

failed in axial compression within a period of 5 hours after removal from

the curing bath.

Constant rate of strain axial loading was provided by a load frame pur-

chased from Research Engineering of San Pablo, California. The loading

component consists of a hydraulic piston that is pneumatically pressured.

Vernier needle valves allow control of oil flow to the piston resulting

in controlled rates of axial strain. The loads were transmitted to the

samples through a load rod with a hemispherical tip contacting a conical


seat on the sample top platen. The load rod was supported at the triaxial

cell by a Thompson linear bushing assembly that maintained cell pressure

with a close tolerance air bushing. Residual load rod friction at the

bushing was examined and found to be negligible.

Before loading the samples, the strain rate was set to 15 percent per

hour. Variation in sample stiffness," as a function of strain, required

that the rate be monitored and periodically adjusted during loading.

Samples were taken to 15 percent axial strain.

Data readings included axial deformations from a dial gauge accurate to

2.5*10 3 mm, axial loads from ans-type load cell with a maximum capacity

of 4.5 KN, and volume change with the graduated burette mentioned previ-

ously. The data was recorded by hand and subsequently stored on an Apple

IIe microcomputer diskette. Data reduction was executed with a modified

Basic language program, originally developed by Allen Sehn at Virginia

Tech that includes: area corrections, stress and strain calculations,

density determination, maximum deviatoric stress, axial and volumetric

strain at failure, and initial tangent modulus. General sample deforma-

tion was qualitatively noted at failure and at the end of each test.


5.3 CYCLIC TESTING

5.3.1 Introduction

The goals of the cyclic testing program are to provide an indication of

the effects of nonhomogeneous cementation on liquefaction resistance and,

if possible, to quantify the cyclic behavior of cemented sands in general.

The laboratory procedures used are described by Silver (1976) and Silver

et al. (1976). Since all samples are artificially created it is possible

to control both the level of cementation as well as the sample density.

In order to compare the effects of three different levels of cementation

and one layered, or· nonhomogeneous, material an attempt was made to

maintain constant densities of approximately 15. 70 KN/M 3 throughout the

testing program. Liquefaction resistance curves were generated for sam-

ples with 0%, 1%, and 2% cementation, and for 2% cemented samples with a

one centimeter middle layer at 1% cementation.

5.3.2 Method of Loading

A variety of laboratory methods are available for the evaluation of

liquefaction resistance of sands. These include the cyclic triaxial,

simple shear, and torsional shear, as well as cubical shear devices. Of

these, the cyclic triaxial test is the most widely performed due to its

relative simplicity and availability. Consequently, this is the best


understood and most standardized test (Silver, 1976).

effort, only the cyclic triaxial test was utilized.

In the present

The testing technique that was followed, for the isotropically consol-

idated, undrained, cyclic triaxial tests, is described by Silver {1976)

and will not be repeated here. Appendix B, however, includes a procedural

outline, highlighting some specific considerations for the particular

equipment used in these tests. The basic test arrangement is shown in

Figure 5-1. The axial loads applied to the samples in the stress con-

trolled tests were sinusoidal in nature and provided by a closed loop MTS

servo-hydraulic system.

The axial loads were monitored with an s-type load cell, conditioned to

give a full scale output of ±100 pounds. For accurate excess pore pres-

sure measurements, a differential pressure transducer with a range of 0

- 50 psi was placed between the cell pressure and the sample. Axial

displacements were monitored with an LVDT (linear variable differential

transducer) mounted above the load frame actuator. The loads were con-

trolled with the MTS 445 controller and 410 digital function generator,

and verified with a Tektronics 502A oscilloscope. A multi-channel

Honeywell light beam recorder provided a permanent record of the loads,

axial deformations, and pore pressures during testing.


V1 N

HONEYWELL VISICORDER

MTS SYSTEM 410 FUNCTION

GENERATOR

445 CONTROLLER

406 CONTROL UNIT

DIFFERENTIAL PRESSURE TRANSDUCER

·1· I I I

I I I I I I I I LVDT

r ..L-L-, I

:HYDRAULIC 1 ACTUATOR I

I

Figure 5-1: Schematic of cyclic testing equipment.

At the outset of this research project, state-of-the-art loading and

monitoring components, including the MTS controller and the Honeywell

Visicorder Oscillograph, were newly purchased. The controller, coupled

to an existing 10 kip load frame, replaces an earlier model used in this

investigation to help develop a test procedure. The initial effort was

directed at assembly and calibration of the test system shown schemat-

ically in Figure 5-1. A user's guide, describing the equipment and its

use in performing liquefaction tests, was developed to aid in procedural

continuity at the VPI Geotechnical Laboratory (Milstone, 1985).

Prior to testing, samples were saturated and consolidated to 103 KN/M2 ,

to be consistent with previous work. To insure isotropic consolidation,

a static axial compression load was applied to the sample to compensate

for the reduction in this stress direction due to the upward action of

cell pressure on the loading rod. Samples were allowed to drain at the

top and bottom during consolidation. The resultant volume change and

axial strain were recorded following a 30 minute consolidation period,

for determination of sample density and area at the time of cyclic load-

ing. Consolidation volume change was monitored with a graduated burette

connected to the drainage lines, while axial strain was measured with the

MTS lvdt.

The samples were subjected to cyclic loads of a sinusoidal nature with a

frequency of 1 cycle per second, as is standard practice. The amplitude


of the loading function is calculated from the chosen stress ratio, S , r

which is defined as:

S = !:io / 2o ' r c (5. 1)

where: !:io = maximum deviatoric stress

o ' = consolidation stress c

For each stress ratio, cyclic loads were continued until liquefaction was

achieved and cyclic strains appeared to have stabilized. Testing was

halted if liquefaction had not occurred within five hundred cycles. Ad-

ditional tests were performed on similar samples at a range of stress

ratios until a complete liquefaction resistance curve could be developed.

Analysis of the cyclic t~st data also includes an investigation of the

rate of pore pressure buildup in the various materials. This is discussed

more extensively in Chapter 7 along with the other cyclic test results.

S.3.3 Typical Results and Verification of Procedure

During the cyclic triaxial tests, axial loads, axial deformation, and

generated pore pressures are continuously recorded with the Honeywell

Oscillograph. A typical set of results from such a test, performed on

cemented sand at a stress ratio of 0.35, is presented in Figure 5-2. The

measured loads and deformations are converted to represent axial stress

and strain, respectively.


_l_.----

=:? I :t 1~ :. · . %-d q =2 2, . c ~·--<-,, --------- Ii_ l - ---t-

I;: I.

' ; "'F'

~

~--=---=- -_;_:-·:-·· I'•

t==

===·:;;::::§== -_ -· -· _.::_ --

! i ! ! . I, i I r,,

1 I I I i I ~ I It I I

I i I I I I 11 '

I ! ii ! i- l 1 I I I i ' ! I

'·

! ! I I ii i I : I l ~ I i ! I I f?i I I! i Ir i I i i :

I I I 11 ' i ~~' ' Ii I P: I I i ' ' I ' : I I I I i 11 p ! I I I [. I ' ! 11 i I

I ! I I :~ I I I I I 11 I I .. ~1 I I i l

11 i I I Ii I I ! I I I i I , i: i I 1 1 .i.. i I 11

I 'I : I i I! i .> ii I i 11 I I I I i I I 1..,µ.. ~! i l !

i I i Ii : i I) I I i Ii : i; i ! Ii I: I I ~i Ii I Iii ' I I i I' ! !~ i I': i, i I 11 i 11 I I

I i : ' ' IT i ! di 11 i.;; i I : . I i. ! I 111 I i : • ; 111 I i i ! l I : ! I I ; I 1-

l l i i i I I

' i i ' : l I i I i i I i I I I I I·~ I ~ I i i I i I I I I I ! i I I i i I

1 ~ : I i 1 1 : 1 1 111 11 1 1 .1 ;j ~ 1 1 1 :-n 1 1 1 i 1 ··1 1 1 1 1 1 r.: II\. I I il'li I . ; i 1: '.t\11 i• i :.,1 I j i'"t ! * 1 r I I I! If! I 111 i ! ! : , i

rt01 S~'3'1W \i.aO') . c-.01s!'GJ,lr.!! 1 r I i j F; ! ,: ! I I : i I I I ! ! ! I I J,1' 1 I I i : i ; I

' Figure 5-2: Typical results of a cyclic tria.xial compression test.

TEST PROGRAM, METIIODS, AND EQUIPMENT 55

The cyclic shear stress ratio can be verified from these plots by first

dividing the peak double amplitude cyclic load by two times the consol-

idated sample area, to determine the maximum deviatoric axial stress.

This value is then divided by two times the effective confining pressure

to evaluate the shear stress ratio.

The standard method of presentation for liquefaction studies is referred

to as the cyclic shear resistance curve and is a plot of the stress ratio

versus the number of cycles to liquefaction. An example of this, after

Silver (1976), is shown in Figure 5-3. This curve represents initial

liquefaction for Monterey #0 sand samples prepared by a tamping method.

The figure presents results of essentially identical liquefaction tests

on similar material, performed by eight independent laboratories.

Prior to the purchase of the more advanced MTS system, an older MTS 406

control unit was available to the researcher. Since sand samples had not

previously been successfully liquefied at Virginia Tech, it was necessary

to develop and verify a proper test procedure. This effort yielded re-

sults from a family of six tests on tamped Monterey #0/30 sand samples

which are included on Figure 5-3. It is observed that the data generated

by the early procedure falls in the general range of the 'standard'

Monterey #0 curve developed by Silver and others (1976), plotting somewhat

lower than the results presented by Muzzy (1983) for Monterey #0/30 sand.


SUMMARY CURVE

MONTEREY SAND NO. 0 O.BL-~~~~~~~~+-~~~~~~~~~

WET TAMPING COMPACTION t),,t) <1 N

11 a: '11 0.6 0 I-<( a: (/) (/) w a: I-C/)

INITIAL LIQUEFACTION

10 100

NUMBER OF CYCLES

LABORATORY

1.000

DENSITY (KN/M3)

0 15.49

2 6 15.54

3 0 15.59

4 • 15.32

5 0 15.46

6 • 15.53

7 & 15.60

8 'i;) 15.59

MILSTONE ¢ 15.54 MUZZY EB 15.46

10.000

Figure 5-3: Cyclic shear resistance curve for uncemented Monterey #0 sand (after Silver, 1976).

Monterey #0/30 sand is used in this project because it is similar to the

Monterey #0 sand used in previous investigations but no longer available

from Lone Star Industries. Comparisons of the two materials are presented

in Chapter 3.

As noted cyclic data on tamped Monterey #0/30 sand tested by Muzzy (1983)

has been plotted on Figure 5-3. His work concludes that this sand has a

higher cyclic shear resistance than does Monterey #0, as demonstrated by

this curve. The relatively lower liquefaction curve initially developed

in the present investigation for Monterey #0/30 sand suggested that re-

finements to the testing procedure were necessary.

Cyclic testing was improved with the arrival of the more advanced MTS

loading system, use of pluviated samples, and modified testing methods

that strictly comply with the requirements of the standard cyclic testing

procedure described by Silver et al. (1976). These include attention to

the sample uniformity and saturation, loading equipment, and to load and

pore pressure measurement devices. To insure that the present procedure

is compatible with the standard practice, a comparison was made with

documented results of pluviated Monterey #0 sand samples tested by Mulilis

et al. (1977).

Figure 5-4 presents a plot of cyclic stress ratio, S , versus the number r

of cycles to initial liquefaction, N1 . , for the results of Mulilis et iq

al. (1977) and this investigation. The data in this figure represent the

condition of initial liquefaction, where the induced excess pore pressure


is first equal to the effective confining pressure. It is noteworthy that

the curves have similar shape. As expected, the Monterey #0/30 sand from

this investigation is more resistant to liquefaction than the Monterey

#0 sand due to higher density and the slight, inherently higher resistance

shown by Muzzy (1983).

Peak values of stress ratio, strain and pore pressure for a test on 2%

cemented sand are given in Figure 5-5. This method of presentation shows

that deformation remains minimal until the onset of liquefaction. This

behavior was exhibited in all of the tests, and is investigated more

closely in Chapter 7.

The stress ratio can be seen to remain relatively constant throughout most

of the test. It is observed, however, that as axial strains become ap-

preciable, the stress ratio begins to drop off. While the cyclic testing

device is operating in a stress controlled mode, it is unable to keep up

with the large deformations. This is typical of many dynamic testing

devices. The concern is minimized, though, since the stress ratios gen-

erally remain constant through the onset and initial development of

liquefaction. The phenomena described above and shown in Figure 5-5 were

compared to, and found to be consistant with, peak result trends presented

by others (Silver, et al., 1976; Rad and Clough, 1982). It is felt that

this serves as additional verification of the cyclic testing procedures

adopted for the present investigation.


0.55

0.50

~ 0.45

0 0. 40 !-CI a: 0.35 (j') (f)

~ 0. 30 t-(f)

a: 0.25 CI l..LJ

~ 0. 20 u ~

u >-

0. 15

u 0. 10

0.05

0.00 2 5

I I

I I

I I

AVG. DENSITY = 15.40 KN/M 3

UNCEMENTED INITIAL LIQUEFACTION

M!LSrnNE M~NT.•0/30-('.)

MULl LIS M~NT. •O

15.58

! I I I

10 20 50 100 200 500 1000 NUMBER QF STRESS CICLES, N

Figure 5-4: Cyclic shear resistance curves for uncemented sand.


(f)

~ ~ 'a:: .28 - - minimum allowable stress = 0.8 SR - - -a:: <( (f) f- 0:: I (f)

_J 2 ~<(~ x a:: -<( 1-

(f)

w Oz ::::>-I- <( - a:: ci I- -~ (f) ~ <( -_J

<(

~~ CD

i5 c

.25

c 0 ·c;; ., Q) ... Q.

~ (.)

5

0

-5 10

5

0

100 - - - - - ~ - - - - - -·

"-Initial Liquefaction I

~ ;:JO)

0• 0.. WC\J

a:: :E 0 2 ....... 50 w ,,, z (.) ~ ::.::: ::::::>a:: -0 a.. ~

-----0 2 3 4 5 6 7 8 9 10 20 30 40 50 70

NUMBER OF STRESS CYCLES, N

Figure 5-5: Peak results from a cyclic triaxial test on 2% cemented sand.

TEST PROGRAM, METHODS, AND EQUIPMENT

100

61

6.0 STATIC BEHAVIOR OF CEMENTED SANDS

6.1 INTRODUCTION

There are three primary goals of the static testing phase of this study:

1. To gain insight into the effects of cementation on volume

change. This allows investigation of the critical void ratio

concept as it applies to cemented sand. The information can

also be used to seek correlations with liquefaction resistance.

2. To observe the effects of a weak lens on the static strength

properties and volume change characteristics of more strongly

cemented sand.

3. To add to the existing data base of controlled cemented sand

triaxial tests, and to provide a quantitative measure of the

cementation. This provides some basis of comparison with which

to evaluate the effects of weak lenses.

Eleven consolidated drained triaxial were performed on a family of 2%

cemented sand at densities of 15.00, 15.45, and 15. 70 KN/M 3 , and on a

second group of 2% cemented samples at a density of 15. 70 KN/M 3 • The

second set of 2% samples included a weaker, 1%, layer formed at midheight.

The creation of the samples is discussed in Chapter 4, and the testing

STATIC BEHAVIOR OF CEMENTED SANDS 62

procedures are detailed in Chapter 5. A limited number of unconfined

co~pression tests were performed on the homogeneous material for cali-

bration purposes.

6.2 HOMOGENEOUS DRAINED BEHAVIOR

The 2% cemented samples at average densities of 15.00, 15.45, and 15. 70

KN/M 3 were tested at confining pressures of 69, 207, and 345 KN/M2 •

Stress, axial strain, and volume change were monitored with a load cell,

dial guage and graduated burette respectively. Stress-strain and volume

change plots from the three sets of tests are presented in Figures 6-1

to 6-3. Note that compression failure, which is taken as peak deviatoric

stress, generally occurs at axial strain levels of approximately 6% to

7%. All samples show volumetric contraction up to axial strains of 1%

to 2%, whence they begin to dilate. The information derived from these

tests is also organized in tabular form (Table 6-1).

It can be seen that both stiffness (initial tangent modulus) and peak

stress increase with increasing density and confining pressure, as is the

case for uncemented sands. Peak strength envelopes for these materials

are defined from p-q diagrams shown in Figure 6-4 to 6-6. Unconfined

compressive strengths were calculated from the resulting friction and

cohesion parameters. A summary of this information is shown in Table 6-2,

which includes strengths generated from Mohr's envelopes and from the

unconfined compression tests. Trends are consistent with those noted by


15 I

1 Ll >--

13 -

12 -

1 I -C't 10 -0 --' C't 9 ~ ~ ..... . . . z ~ 8 -

('I) 7 -0

6 -... 0 5 -

Li - .. . 3 -. "

I I

2 3 I

5

I I

. . .. . .

! AVG. DENSITY • IS.OOKN1M> 1 27. CEMENTED SYMBOL 0 c Y,l,M':

! I I

0

• 0 0

'59 2C~

'3"-:CS

0 0 0

-

-

-

-

-

-

-

-

6 7 8 9 10 11 12 13 1 Ll 15 16 AXIAL STRAIN (%1

0 1 2 3 4 s 6 7 8 9 10 11 12 13 14 15 16 5 ..---.-~.....--.-~...----...~...----.-~...---.-~~--.-~....---....~-.---.~....,......,

N ll

z 3

~ 2 ..... en

EXTENSrnN

o"'

l!J

"' " 0

"' 0 0 0

• 0 0

(!) • 6 • .. .. ... 0 0 0 " 0 0 0 0 0

. . . LU ""•"' ~ 0 'IE"~+-~-+-~--r.,.,..."'-"'+0 ---;;:-"-!7~--r--'+-~-+~--+~--,r--~t--~+-~-+-~-'+-~-t-~--t~~r--1

000 l!l 0 ~ ~ .a

...J ~"""'~l!lc""" o o • r""\. •a;"~OOC!IC!HJO O a • > -1 ................. .

CONTRACT 1 ON

Figure 6-1: Stress-strain and volume change plots for 2% cemented samples with average dry density= 15.00 KN/M 3 •


15

14 >--

13 >--

12 I-

11 >--

Cll 10 a --' Cll 9 :r:

' z 8 ~ ,_

C'll 7 I-

b 6 I-...

b 5

00

50

N 4

z 3 -a: 2 a: I-U"l 1 IL.I %: 0 ::::> ...J 0 -1 >

.·

. .

1 2

1 2 EXTENSlON

. . • . . .

.. · .· .··

' 3 4

3 4

5

5

olll 11i"~ .,,,.

~"' °""'"' o'ln"'1~

:i,,'b•

CONTRACTION

.. .,,, .,,, .... ... . .

6 7 8 9 10 AXIAL STRAIN (%)

6 7 8· 9 10 • 0.

~o (Jo 0

oP d!l

"" ""' "" "" 00 ... ,.,ec

..

I AVG. DENSITY • 15.llSKNtH3

I 27. CEHENTEO

1 1

I

1 1

1 1 0 0 c

SlMBClL [!] I!)

I

12 13

12 13 o1 o ~I 0

.

!1 e 9<NtM2J

69 69 207 345

. . .

14 15

14 15 ::;ii O

. . . 0 • .

-

-

-

16

16

Figure 6-2: Stress-strain and volume change plots for 2% cemented samples with average dry density= 15.45 KN/M 3 •


15 ..-~-..-..-..-..-.....,..... ........ _I ................................................................................................................................................................. ~

Ji AVG. DENSITY • 15. 70KN1M, 2X CEMENTED

14 >--

12

1 1

0

·• 0

"" 0 "'

I I I

1 207 345

! 4> C!I c:i !!I., o C!:I :a e o o ~ o ~I!) o o .'!l l!l o--L---1-----------l

~ 0 ~ ~ c

-

-" 0

(I) 7 0 "

c •• • l!I .-

" • 6 -5 - 0

"

0 " 3 1-- l!I

" " • 2 -"

" l!I

1 " I

1

"'

l!I l!I

" "'

I

2 3 I ;

4 s 6 7 8 9 10 11 AXIAL STRAIN l%l

12 13 14 15

-

-

-

-

16

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 s------....----.---......----.-------------------------------------

z cc a: I-C()

3

2

EXTENSJON

rnNTAACT rnN

• • l!I " . "

Figure 6-3: Stress-strain and volume change plots for 2% cemented samples with average dry density= 15. 70 KN/M 3 •


Table 6-1: Sample conditions and test results of CD triaxial tests on 2% cemented sand and nonhomogeneous samples(l2-14).

INITIAL DENSITY CJ3 I PEAK sif EVf TANGENT

TEST STRE§S MODULUS (KN/M3) (KN/M2) (KN/M ) (%) (%) (KN/M2)

1 14.96 69 279 5. 7 1. 62 44750

2 15. 10 69 305 5.3 1. 05 40210

3 15.04 207 640 6. 1 0.66 69140

4 15.05 345 997 6.8 0.60 76738

5 15. 40 69 330 4.8 1. 70 66004

6 15.39 69 314 4.5 1. 58 59416

7 15.53 207 837 6.9 1. 39 79418

8 15.48 345 1220 7. 1 0. 73 98179

9 15.67 207 876 7. 2 1. 48 71740

10 15. 71 207 976 o.9 1. 54 80797

11 15. 73 345 1245 6.8 0. 74 114115

12 15. 26 69 297 5.6 1. 86 41840

13 15. 33 207 757 7. 1 . 65 74508

14 15. 47 345 1149 7.3 .91 110320


Rad and Clough (1982). Specifically, the cementation manifests itself

as an apparent cnhesion that increases with increasing density. Conse-

quently, unconfined compressive strengths are also seen to rise.

Table 6-2 includes test results from cemented sands that have been studied

by other researchers. For the most part, friction angles are quite sim-

ilar for all the investigations. However, there are differences in ap-

parent cohesion and unconfined compressive strength. It is suspected,

for similarly prepared artificially cemented soils, that relatively minor

differences in sample preparation technique, cement quality, distribution

throughout sample, and curing time are major contributors to the strength

differences.

Figure 6-2 and Table 6-1 also include test data from the crumbled and

reconstituted, 2% cemented sample. Notice that both the stress-strain

and the volume change behavior of this disturbed material are similar to

that of the undisturbed cemented sample at a similar density. It is ex-

pected that additional testing would bear out previous results; namely,

that disturbance of the cementation lowers the static strength, but has

a relatively small effect on volume change characteristics. This possi-

bility is supported by the observation that most of the volumetric ex-

pansion takes place after 2% axial strain; a point where much of the

cementation has been destroyed even in initially intact samples.

While liquefaction potential has been related to the density of uncemented

sands, it has been shown that this is not the only controlling parameter


in cemented soils. Volume change seems to be a better index of the cyclic

behavior of cemented sands. This material property can be assessed by

in-situ means such as the self-boring pressuremeter, and is preferable

to measurements of cementation which are difficult at best.


800

600

Milstone - Yd=lS.00, ¢=34, C=40 II

C" 400

200 P=34, C=26

'( d= 14. 61' ·:P=34' C=l2

0 0 200 400 600 800 1000

p = ( 0"'1 + O"~) 2

Figure 6-4: p-q Diagram (average dry density= 15.00 KN/M 3 ).


c

800

]N 600

~ Milstone - Yd=lS.45, ¢=36, C=60 ~

?" II

~ C" 400

- Yd=lS.34, ¢=36, C=40

200

Rad - Yd=lS.23, ~=36, C=20

0 --~~~~ ...... ~~~~--~~~~--~~~~--~~~--0 200 400 600 800 1000

Figure 6-5: p-q_Diagram (average dry density= 15.45 KN/M 3 ).


II

O"

800

600

400

200

~ilstone - ~d=lS.70, P=JS, C=85

t,=J7, C=58

Rad - ~d=L6.07, ~=39, C=30

0 --~~~-----~~~---i~~~~--a..~~~~.....i..~~~~~ 0 200 400 600 800 1000

Figure 6-6: p-q Diagram (average dry density = 15. 70 KN/M 3 ).


Table 6-2: Results of CD triaxial tests on 2% cemented sand.

MOHR'S p-q RESEARCHER, DENSITY e) c ucs ucs

SAMPLE (KN/M3) (DEG!{EES) (KN/M2) (KN/M2) (KN/M2)

RAD 14. 61 32 20 73 72 1% CEMENT 15.23 35 26 95 94

(PLUVIATED) 16.07 39 20 83 80

REYES 14.62 31 11 46 42 1% CEMENT 14.89 33 8 29 26

(PLUVIATED) 15. 32 36 22 86 66

MILSTONE 15. 46 37 30 120 104 LAYERED

MILSTONE 15.00 34 40 150 141 2% CEMENT 15. 45 36 60 236 167 *

(PLUVIATED) 15. 70 35 85 327 331/95

RAD 14.61 34 12 45 64 2% CEMENT 15.23 36 20 79 95

(PLUVIATED) 16.07 39 30 129 111

SITAR 15. 51 34 46 173 (2% TAMPED)

* 95 KN/M2 from unconfined compression tests.


6.3 EFFECTS OF NONHOHOGENEITY ON CEMENTED SAND

Nonhomogeneous samples prepared for this investigation were subjected to

consolidated-drained triaxial tests, performed at confining pressures of

69, 207, and 345 KN/M2 • The samples were comprised of a 15 cm tall sample

at 2% cement content with a one centimeter thick, weaker, 1% lens at

midpoint. Sample preparation is discussed in Chapter 4.

The stress-strain and volume change data are plotted in Figure 6-7, and

key results are included in Table 6-2 along with those for homogeneous

samples.

The weak lens is seen to lower both the peak stress and the stiffness of

the stronger mass. By plotting the peak test data in p-q space (Figure

6-8), it can be seen that the friction angle of the layered material is

not significantly changed from that of the 2% homogeneous material.

However, the cohesion intercept definitely decreases as a result of the

weaker cementation at the sample centers. The reduction of the apparent

cohesion is to approximately half that of the homogeneous 2% mass. There

is an associated drop in unconfined compressive strength due to the weak

lens to a value of approximately half that of the homogeneous material.

While all of the cemented samples exhibited bulging deformations at the

time of failure, the nonhomogeneous samples had a more exaggerated bulge

toward midheight, in the vicinity of the weak lens.


15

14 -

13 -

12 -

11 f-

('<

10 0 ...... ...I

('<

9 L ' z 8 f-~

(I) 7 b

6 -b~

5 ij

50

~ 4

z 3 -a: 2 a: I-fJ') 1 LU 2: 0 :::> _J 0 -1 >

-2

. 0

•

1

1

" 0

I

2

2

. .

EXTENSrnN

3

3

CCINTRACTl(]N

4

4

5

5

" "

6 7 8 9 AXIAL STRAIN

6 7 8 9

" " l!I

l!I

I AVG.DENSITY• 15.70KN1H' NONH0110GENEOUS

-

. . .

l!I 0

1 0 11 (%)

1 0 1 1 I

l!I l!I l!I 0

S'(M80L <Jc iKN;M'I

I

12 13

12 13 I

l!I l!I

I

14

14

69 207 345

I

15

15

I

-

-

-

-

-

-

-

16

16

Figure 6-7: Stress-strain and volume change plots for nonhomogeneously cemented samples.


800

]N 600

Yd 15.46,¢ 37° c 30 '

II

er 400

200 -

0 .__~~~....L...~~~--IL--~~~....L-~~~---'-~~~---J 0 200 400 600

Figure 6-8: Peak strength envelope for nonhomogeneously cemented samples.

STATIC BEHAVIOR OF CEMENTED SANDS

800 1000

76

6.4 VOLUME CHANGE BEHAVIOR

6.4.1 Volumetric Strain Characteristics

When a sand is sheared in drained conditions there is typically a tendency

for volume change. For example, looser samples densify. In undrained

conditions with a saturated, loose sand, this leads to increasing pore

pressures that can cause liquefaction in cyclic loading. Denser materials

can dilate during drained shear; in undrained loading pore pressures are

reduced, minimizing strains and the likelyhood of liquefaction. Theore-

tically, then, if cementation serves to alter volumetric response, the

result could indicate changes in liquefaction resistance.

The drained static compression test results from this and other research

(Singh, 1984; Reyes, 1983; Rad and Clough, 1982) can be used to examine

this issue. Included in the data set are results from tests performed

on uncemented Monterey #0 and #0/30 sand, as well as the same sands ce-

mented with 1% and 2% Portland cement, by weight. For a variety of den-

sities, tests were executed at a range of confining pressures. Volume

strain at failure (peak stress) is plotted versus initial dry unit weight

for tests at similar confining pressures (Figures 6-9 to 6-11).

Analysis of the resulting plots reveals no clear trends of volume change

at failure as a function of cementation. Volumetric strain at failure

does not appear to differ to any significant degree for different levels

of cementation; any apparent differences are inconsistent. The basic


conclusion from these figures is that the absolute magnitude of volume

strain is independent of cementation. Thus, there appears to be no basis

to believe that cementation has a major effect on liquefaction resistance

through the volume changes, per se, of the soil.

6.4.2 Effects of Cementation on Rate of Volume Change

The rate of volumetric expansion during shear has been proposed as a pa-

rameter that can be related to liquefaction resistance (Vaid, et al.,

1981). The expansion rate, or dilation rate, is characterized by the

dilation angle, v, which is the inverse sine of the slope of the volume

expansion curve. This is expressed as:

sin v = oV / oo ( 6. 1)

where: av = change in volume

oo = change in shear strain

Vaid and others have shown dilation angle to be linearly related to rel-

ative density of uncemented Ottawa test sand, demonstrating that materi-

als of higher relative density are characterized by higher angles of

dilation. Dilation angles, as measured from a drained laboratory or

in-situ test, can then be related to liquefaction resistance as a function


~

;;-..:

> ~

. z a: a: I-(/)

i.J :::c ~ ....I 0 >

3 <J = c 103 KN/SM (!) iJNCEMENTEO m '--'

2 ~

Q]

.<!>. 0

-1 lY.5

l i: 2%

!'.!)

CEMnJT CEMENT

C) ~

.<!I. Q]

8

(:'.)

15.0 15.5 16.0 DRY UN I T WE I G HT , 14 IK N ;M 3l

16.5

Figure 6-9: Volume strain at failure for CD triaxial test versYs initial dry unit weight (confining pressure= 103 KN/M 2 ).


3 (5 = c 207 KN/SM Q) UNCEMENTED

;;--.: ¢ NONHOMOGENEOUS 2 12] Ii'. CEMENT

> 6 2i'. CEMENT '4) ['] 6

6 ['] z (')

a: cc CJ I-(/)

(') w 6 L!'.

,!',

::::E ~ :::::) _J 0 ['] 0 > 6

-1 14. 5 15.0 15.5 16. 0 16.5

DAY UN IT WE I GHT, dd o<N1M 3l

Figure 6-10: Volume strain at failure for CD triaxial test versus initial dry unit weight (confining pressure= 207 KN/M 2 ).


3 <5 = 3 L! 5 KN/SM c ~ UNCEMENTEO

~ ¢' NC ~J HOM 0 GEN EO US 2 ['] 1 i'. CEMENT

> A 2% CEMUJT ~ ['.]

C) z a:

['.]

CL I-<J)

(')

w ~ ::::> _J 0 0 >

['.]

-1 14. 5 1 5. 0 15.5 16. 0 16.5

ORY UNIT WEIGHT, rd IKN1M 3 l

Figure 6-11: Volume strain at failure for CD triaxial test versus initial dry unit weight (confining pressure= 345 KN/M 2 ).


of rela~ive densi~y. For this research project it ~as desired co knc~

whether dilation angle is affected by cementation.

All the dilation angles reportP-d herein were determined from consolidated

drained triaxial test data where volume change was measured directly from

s3mple drainage lines. Dilation angles were calculated from the =esulting

volume change curves (as shown in Figures 6-1 to 6-3) and from estimated

shear strains. Shear strain estimates are necessary because only axial

strains were monitored during the reported tests. By assuming right

circular cylinder deformation, shear strains may be calculated thusly:

knowing: 0 = (6.2)

( 6. 3a)

= z.l(A /TT) c (6. 3b)

(6.3c)

Substituting:

o = e L + 1 - ( 1. 12 8 ID . ) ( ./V . Cl - e V) I ( L . (1- e L) ) ) l. l. l.

( 6. 4)

Where: o = shear strain

e1 = axial strain

eH = horizontal strain


,,. = volumetric strain ~v

D. = initial sample diameter l

Df = final sample diameter

L. = initial sample height 1

V. = initial consolidated sample volume l

A = corrected sample following strain c

Equation 6.4 was applied to test data and found to give results close to

This is consistent with the elastic theory assumption of

Poisson's ratio equal to 0.5 for a saturated, incompressible sample.

Dilation angles were determined for the portion of the volume expansion

curves that is representative of sample failure. This analysis was exe-

cuted on uncemented sand data as well as data from samples containing 1%

and 2°0 cement by weiglit. These data are plotted in Figures 6-12 to 6-14

for respective confining pressures of 69, 207, and 345 KN/M 2 • Al thongh

there are a limited number of points, cemented sands appear to display a

linear rel3tionship between density and dilation angle. There is also a

consistent trend of increased dilation angle with increasing levels of

cementation. Tims, while absolute volume change v;as not affected by

cementation, the data in this section show that cemented sands reach a

given level of volume change at a rate faster than their uncemented

cousins. The difference between the two increases as cementation in-

creases.

STATIC BEHAVIOR OF CE~E~TED SANDS 83

As mentioned previously, it has been difficult to sample or test most

cemented materials in the field without first disturbing the cementation.

Consequently, liquefaction resistance of these natural deposits may be

underestimated. The self boring pressuremeter has the capability of

measuring the rate of volume change, or the dilation angle. With no other

indication of cementation, increased dilation angles are likely to be

interpreted as higher density uncemented sand. Nevertheless, it is pos-

sible that the cyclic strength determined from the apparently higher

density will adequately reflect the cyclic strength of the actually

looser, but cemented, deposit. Repeated tests, at the same location, may

also give an indication of the presence of cementation by yielding lower

dilation angles on subsequent, disturbed, tests.

6.4.3 Critical Void Ratio

As one of the objectives of this research, it was intended to investigate

the application of Casagrande' s critical void ratio concept ( 1936) to

cemented sands. For this purpose, volume change at failure from drained

compression testing is plotted versus initial void ratio (Figure 6-15).

For each confining pressure, graphical interpolation of the data provides

an initial void ratio at which, theoretically, there would be zero net

volume change at the point of maximum shear stress. These values are

plotted versus the respective confining pressures to develop the critical

void ratio curve. An example of this is shown in Figure 6-16. A similar


40 (j) <5 = 103 KN/SM w c w C) UNCEMEIHEO cc

CJ 1% CEMrnT c...:i w 30 <!; 2% CEMENT 0

~

w _J 20 (..,:) z a: z El

t- 10 a: _J ..... Cl

0 14. 5 15.0 15. 5 16. 0

DR Y UN I T W E I G HT , 1 d IK N 1M 3)

Figure 6-12: Dilation angle versus initial dry density (consolidation pressure = 103 KN/M 2 ).


16.5

85

Cf) w w a: (.!)

40

~- 30

-~ . w _J 20 (.!) z a: z 0

..... 10 a:: _J

Cl

0

(J = 207 KN/SM c (!) UNCEMENTEO CJ ! ".' CEMENT .<!> 2% CEMENT

14. 5 15. 0 15.5 16.0 DRY UNIT WEIGHT, 1• IKNtM 3)

Figure 6-13: Dilation angle versus initial dry density (consolidation pressure = 207 KN/M 2 ).


16.5

86

Cf) w w a: L') w a

~

w _J L') z a: z El ..... I-a: _J ..... a

40 (J = c 31.!5 KN/SM Q) UNCEMENTED ~ 1 i:: CEMENT

30 a 21. CEMENT ~ NCJNHCJMCJGENECJUS

20

10

0 14.5 15.0 15.5 16.0

DRY UN IT WE I G HT , "{ 4 tK N !M 3l

Figure 6-14: Dilation angle versus initial dry density (consolidation pressure = 345 KN/M2 ).


16.5

87

relationship may also be developed by using residual, or steady state,

volume strain rather than that at failure.

A previous study in this area (Reyes, 1983) noted that cementation appears

to lower the critical void ratio of sands. Reyes tested sands with 1%

cementation. For comparative purposes, the present work produced data

for 2% cemented sands. Test results from other researchers (Rad & Clough,

1982; Singh, 1984) were also reduced in the appropriate manner to enlarge

the data base for this study.

All available data are plotted in Figure 6-17 as critical void ratio

versus confining stress. Both the 1% and 2% cemented sands appear to have

lower critical void ratios than the uncemented sand. The reasons for this

finding are not clear. It may be that the conventional critical void

ratio concept is simply not applicable to cemented sands, since the volume

change values used in developing the diagram are those at large strains,

where cementation bonds have already broken down. The maximum influence

of the cementation lies at low strains; a level where uncemented sands

have yet to mobilize their shear resistance. In addition, it is likely

that the zone of failure in the cemented samples is confined to a smaller

area; that relatively less sample is involved in dilatent behavior than

in the uncemented samples. Density calculations, which average the volume

strain in the failure zone over the entire sample, would result in ap-

parently low void ratios leading to the behavior shown in Figure 6-17.


c: 0 (/)

w c: a:: g_ ::::::> x .....J Q)

~ ~

w ~ c: ::::::> 0 .....J '.;: 0 (.) >c .... -c:

0 (.)

e init.

Figure 6-15: Volume change at failure from CD triaxial tests versus initial void ratio.


ea

0 I j::: <t a::

I a 0 > ___ l ...J <t eb j:::

I I ~·

-t -1-ec I I

0-a (j"b 0-c

EFFECTIVE CONFINING PRESSURE

Figure 6-16: Critical void ratio versus confining pressure.


.86

• . 84

.82

....: ·;:: () .80 Q.)

• 0 . 78 f- • <t: a:::

.76 a 0 >

.74 _J <t: . (.)

i='. .72 ii:

(.)

.70 • - Uncemented • - 1°/o Cemented

.68 • - 2°/o Cemented

.64 -----------------------------------------------0 100 200 300 400 500 600 700 800

EFFECTIVE CONFINING STRESS, 0-3' (KN/M2)

Figure 6-17: Critical void ratio versus confining stress for cemented and uncemented Monterey #0/30 sand.


7,0 CYCLIC BEHAVIOR

7.1 INTRODUCTION

This chapter presents the results of the cyclic testing program outlined

in Chapter 4. Observations as to the effects of cementation on

liquefaction resistance, in general, are provided and compared to those

of Rad and Clough ( 1982). The test results also provided enough data with

which to examine the effects of cementation on rate of pore pressure

generation and to relate this to strain development during cyclic loading.

Finally, cyclic tests performed on the nonhomogeneous samples revealed

some of the effects that a weak lens has on a more strongly cemented mass.

7.2 EFFECTS OF CEHENTATION ON LIQUEFACTION RESISTANCE

Liquefaction tests were performed on uncemented sand and homogeneous ce-

mented samples with cementation levels at 1% and 2%. To allow comparison,

the average densities are all approximately 15.70 KN/M 3 • Pertinent in-

formation is provided in Table 7-1. The test results are plotted in

Figure 7-1 as the stress ratio versus the number of cycles to initial

liquefaction. Referred to as the cyclic shear resistance, or liquefaction

resistance, curves, each of the curves in Figure 7-1 represent a family

of tests on samples at a different level of cementation. A higher curve

indicates that a greater number of cycles are required for liquefaction,

at a given stress ratio. As expected, cementation has the effect of in-

CYCLIC BEHAVIOR 92

creasing the liquefaction resistance of sands. This trend is also dem-

onstrated when liquefaction is defined as eithe~ 5% or 10% double

amplitude axial strain. It should be noted that the previous work in this

area by Rad and Clough (1982) demonstrates the same tendency.

Taken together, Figure 7-1 and Figure 2-1, which is a similar presentation

of the Rad and Clough (1982) test results, point to another phenomenon.

These plots demonstrate that for samples which liquefied below about 30

cycles, the cyclic shear resistance curves increase rapidly as the number

of cycles decrease. While this behavior is evident for uncemented sand,

it is observably more prominent for the cemented materials. It appears

that cementation, while consistently increasing the liquefaction resist-

ance of sands, has its greatest effect at cyclic loads that are within

the range of duration of probable seismic events. This substantiates the

practical import of continued research efforts concerning the effects of

cementation on liquefaction resistance.

CYCLIC BEHAVIOR 93

Table 7-1: Cyclic triaxial test information.

TEST PERCENT DENS!~ STRESS SKEMPTON NUMBER CEMENT (KN/M ) RATIO B-factor NS% Nl0% Nl. iq

19 0 15.68 . 26 . 96 11 - 10

18 0 15.44 . 25 1. 00 23 - 20

17 0 15.63 . 22 1. 00 101 - 95

16 0 16.07 . 20 . 96 427 - 421

1 1 15. 66 . 40 . 98 - - 7

11 1 15. 75 . 3.5 . 99 20 - 14

2 1 15. 76 • 30 . 98 26 - 19

4 1 15.67 . 25 . 99 45 - 33

5 1 15. 59 . 23 . 99 208 - 200

3 1 15.68 . 20 . 99 - - * 9 2-1-2 15.35 . 45 . 99 6 19 8

7 2-1-2 15. 41 . 40 .99 7 30 10

8 2-1-2 15.35 . 35 . 99 17 59 13

10 2-1-2 15.33 . 325 . 99 17 - 19

12 2-1-2 15.23 . 31 1. 00 39 - 32

6 2-1-2 15.33 . 30 . 98 142 - 120

15 2 15.67 . 55 . 98 25 - 19

14 2 15. 70 . 45 . 98 - - 35

13 2 15. 79 . 33 . 99 221 - 210

* Sample did not liquefy in 560 cycles.

CYCLIC BEHAVIOR 94

0.60 '' I I I AVG. DENSITY • 15.70 KN/M 3

0.55 CEMENT CONTENT VARIED INITIAL LIQUEFRCTION

0.50 2% CEMEN7 CONTE~~~ c:: cc (.{) l % CE~ENT CONTENT 6

0. lJ 5 1;~ OJO N(n ~JGlUEFi ::c: 0 IJNCEHENTEO CJ

I- 0.40 a: cc (.{) 0.35 en lJ..j cc I- 0.30 en cc a: 0.25 lJ..j :r: (.{)

u 0.20 _J u 0. 15 >-u

0. 10

0.05

0. C10 2 5 10 20 50 100 200 500 1000

NUMBER OF STRESS CYCLES, N

Figure 7-1: Cyclic shear resistance curves for cemented sand.

CYCLIC BEHAVIOR 95

7.3 EFFECT OF CEMENTATION ON DEVELOPMENT OF PORE PRESSURES AND STRAIN

Presently, pore pressure and strain development during cyclic loading of

cemented sands are not well understood. It is important to resolve this

issue since if pore pressure generation in cemented sands can be predicted

empirically, effects due to an~icipated seismic events can be predicted.

This aspect of cemented sands is studied here.

One manner of viewing the pore pressure development is given by Lee and

Albeisa (1974). In this normalized presentation, the pore pressure, at

a given stress cycle, divided by the initial confining pressure, is

plotted against the same number of cycles divided by the number of cycles

to liquefaction. Seed and others (197.5,1976) have used this scheme to

develop an empirical method of predicting pore pressure development in

uncemcnted sands, given as:

where: pore pressure

rN' cyclic ratio

( 7. 1)

ratio = U / o ' e c

= N I ~ 1 . iq.

a = exponential factor

This curve has been plotted on Figure 7-3 for a= 0.70. The range of

observed values for uncemented sand as documented by Lee and Albeisa

(1974) is also shown on this diagram.

CYCLIC BEHAVIOR 96

u

b ""' QJ ::::J

::::>

'--

0

t-a: a: w a: ::::) CJ) CJ)

w a: 0....

LU a: 0 0....

1. 0

0.8

0.6

0.4

0.2

0.0 0.0

RANGE OF VALUES FOR UNCEMENTED SAND fLEE 8. ALBEISA, 1975)

0.2 0.4 0.6 0.8

CYCLIC RATIO,

Figure 7-3: Pore pressure ratio versus cyclic ratio.

1. 0

CYCLIC BEHAVIOR 97

Rad and Clough (1982) have shown (Figures 2·2 and 7-4) that weakly ce-

mented sands have a different pore pressure response during cyclic loading

than do uncemented sands. The plot of normalized points for the cemented

materials generally falls above the ranges noted by Lee and Albeisa (1974)

and De Alba et al. (1975) for uncemented materials. The scatter of these

points, which is an artifact of combining results from different tests,

makes further analysis difficult.

The cyclic test data from this investigation is presented in similar

fashion as Figures 7-5 through 7-7. The data from individual tests are

considered in terms of stress ratio level. Only homogeneous samples are

considered; uncemented in Figure 7-5, 1% samples in 7-6 and 2% samples

in 7-7.

Figure 7-5, which describes the behavior of the uncemented sands tested

for this investigation, shows agreement with values documented by Lee and

Albeisa (1974) for typical uncemented sands. This is believed to rein-

force the validity of the procedures used during the present investi-

gation. In Figures 7-6 and 7-7, as mentioned previously, pore pressure

ratio curves from the cemented sands are compared with the Lee and Albeisa

range. As was the case with the data of Rad and Clough (1982), the data

points for the cemented materials plot higher than the uncemented range,

indicating a more rapid pore pressure development than for the uncemented

sands. However, since the curves are classified according to stress ra-

CYCLIC BEHAVIOR 98

lb(J

' ::> I :::J

l.i

.. (S) -r-< c::: w c:::

. :J (f) (f) w 0:: a.. w c::: (S) 0..

1.0 • • • • • I • • • • • 0.8 • • • • • 0.6 • •

• • • • • • 0.4 •• • • Lee and Albeisa

(Observed range for 0.2 uncemented sand)

2% CEMENT 0.00 0.2 0.4 0.6 0.8

CYCLIC RA TI0, r0-N/N1

Figure 7·4: Pore pressure ratio vs. cyclic ratio (2% cement) (after Rad and Clough, 1982).

•

1

CYCLIC BEHAVIOR 99

u

b ........

Q)

::J

L

I--er: a:

::I

UJ a: ::::> (f) (f) UJ a: a.. UJ a: 0 a..

1. 0

0.8

0.6

0.4

0.2

0.0 0.0

KE I STRESS RAT IO 0.200 0.220 0.250 0.260

UNCEMENTED

0.2 0.4

CICLIC AATrn,

SYMBOL

~

x .<!:>

['.]

~ RANGE OF VALUES FOR UNCEMENTEO SANO !LEE ~ ALBEISA, 197Sl

0.6 0.8

Figure 7-5: Pore pressure ratio vs. cyclic ratio (uncemented).

1. 0

CYCLIC BEHAVIOR 100

1. 0

u

b 0. 8 ........

CV :::::l

t-a: a: w

0.6

~ ·O. 4 If) If) w a:: CL

UJ a: 0 a.. 0.2

0.0 0.0

KE I STRESS ART iO 0.230 0.250 0.300 0.350 0.400

1 i: CEMENTED

0.2 0.4

CYCLIC RATIO,

SYMBOL ~

x L!:.

l2J C>

RANGE OF VALUES FO~ UNCEMENTED SAND !LEE lo ALBE 1 SA, 1975!

0.6 0.8

Figure 7-6: Pore pressure ratio vs. cyclic ratio (1% cement).

1. 0

CYCLIC BEHAVIOR 101

1. 0

u

b o. 8 ' Cl) ::J

J-a:: c:c LU

0.6

~ 0. 4 U1 U1 LU c:c a..

0.2

0.0 0.0

KEI STRESS I

RRT!CJ 0.330 0.450 0.550

2i.'. CEMENTED

0.2 0.4

CICLIC RATrn,

51MBCJL

L!>

~

~

RANGE CF VALUES FCA UNCEMENTEO SANO CLEE ~ ALBEISA, 19751

0.6 0.8

Figure 7-7: Pore pressure ratio vs. cyclic ratio ( 2% cement).

1. 0

CYCLIC BEHAVIOR 102

tio, it can be seen that the points outside the uncemented range are as-

sociated exclusively with high stress ratio loading. This is consistent

with the fact that cementation was shown in Chapter 6 to increase the rate

of volume strain under drained, static loading. Higher dilation angles,

as measured in the field, would suggest the earlier and more rapid pore

pressure buildup characteristics of cemented sands.

Further examination reveals another consistent trend. Namely, cemented

sands under low stress ratio loading yield a pore pressure response con-

sistent with that of the uncemented sands. This implies a relationship

to sample deformation which is quantified in these tests as axial strain.

While it is known that axial strain and pore pressure development are

linked, as evidenced by parallel plots of the two (Figure 5·4), the re-

lationship warrants further investigation.

Since the absolute value of axial strain varies with changes in sample

and test conditions, the strains for each test must be normalized before

common trends can be evaluated. Figures 7·8, 7-9 and 7-10, show the axial

strains for the tests of this investigation in a normalized fashion,

similar to the pore pressure generation curves discussed previously. The

strain ratio is defined as the axial strain at a given cycle, divided by

the axial strain at liquefaction. This is plotted versus the cyclic ra-

tio, or cycle number divided by the number of cycles to initial

liquefacton. In all cases, the strains develop slowly until a point where

the rate increases rather rapidly. It is suspected that near the time

that this inflection occurs, the most highly stressed portion of the

CYCLIC BEHAVIOR 103

sample is transformed from a cemented, monolithic mass to a granular ma-

terial consisting of sand grains c~ated with cement crystals.

CYCLIC BEHAVIOR 104

KEY STRESS SYMBCIL AATICI

0.200 e:i 0.220 x 0.250 A

0.260 [!]

·1. 0

UNCEMENTED

a. a .,. -

t.V .........

c· t.V

II a.6 .... '-

. c -I-c:: 0.4 cc z ..... c:: a:. 1:-U'l

a.2

a.a ·· a. a 0.2 O.Y a.6 0~8 1. 0

CYCLIC RATI(j,

Figure 7.-8: Strain ratio vs. cyclic ratio (uncemented).

CYCLIC BEHAVIOR 105

.,.. -w

.......... c:: w

II

. .., '-

. 0 ...... I-a: a: z ...... a: a: I-U'l

1. 0

0.8

0.6

0.4

0.2

0.0 0.0

KEI STRESS RAT !CJ

0.230 0.250 0.300 0.350

11. CEMENTED

0.2 0.4

CICLIC RATIO,

SYMBCJL

C9 x ~

c:J

0.6 0.8

Figure 7·9: Strain ratio vs. cyclic ratio (1% cement).

1. 0

CYCLIC BEHAVIOR 106

-t.J.)

" c: t.J.)

"' L

0

t-a: a: z a: a: t-(.{)

1. 0

0.8

0.6

0.4

0.2

0.0 0.0

KE I STRESS RAT IO

0.330 0.450 0.550

2% CEMENTED

0.2 0.4

CYCLIC RATIO,

SYMBOL

L!'>

(')

[']

0.6 0.8

Figure 7-10: Strain ratio vs. cyclic ratio (2% cement).

1. 0

CYCLIC BEHAVIOR 107

Comparison of the strain development plots with their respective pore

pressure development plots, shows that the marked change in rate of dtrain

precedes the tendency for the pore pressures to develop in a manner dif-

ferent from that of uncemented sands. At low strain ratios, the pore

pressure development of the cemented sands is similar to that of the un-

cemented sands and may be described by Equation 7. 1. Beyond some limiting

strain ratio, on the order of 0.20, the cemented sand pore pressure de-

velopment curves differ significantly from those of uncemented materials.

This limiting strain ratio corresponds to single amplitude axial strains

on the order of 0.7% and shear strains on the order of of about 1.0%, as

estimated by elastic theory. Wissa and Ladd (1964) observed in static

tests that, at this general range of strain, the cementation breaks and

the strength contribution from friction becomes dominant. This behavior

was also noticed by Saxena and Lastrico (1978) who state that, "beyond

certain strain levels there is a gradual breakdown in cementation."

This suggests that, for this type of cemented sand, the cementation does

not affect the trace of pore pressure generation until a certain amount

of strain has destroyed some of the sand-cement bonds. This is substan-

tiated by visual observation of the samples during cyclic loading.

Once this transformation has taken place, the pore pressure generation

curves adopt a different shape than that for uncemented sand. The char·

acter of these cemented sand pore pressure generation curves is then more

closely described by the equation:

CYCLIC BEHAVIOR 108

where: ru, pore pressure ratio

rN' cyclic ratio

B = factor

= u I 0 I e c

= N I N1 . iq.

(7. 2)

Given the cyclic ratio, the pore pressure ratio can be estimated from the

inverse of Equation 7.2:

(7. 3)

Figure 7-11 shows a variety of these curves along with some of the test

data. It is observed that the B-factor increases with increasing stress

ratio. It appears that pore pressure generation for cemented sands cycled

at higher stress ratios, requiring relatively few cycles to liquefaction,

may be predicted by Equation 7.2. At lower stress ratios, pore pressure

generation is described by Equation 7.1 up to a point where the shear

strains exceed about l~. The remainder of the curve can then be approx-

imated by E~uation 7.2, developed for cemented sand behavior. This is

demonstrated in Figure 7-11 by the curves representing data from tests

performed at stress ratios of 0.25 and 0.30.

Prior to developing this concept further, it will be necessary to gain a

better understanding ~f both the mode and the effects of strain in cy-

clically loaded, cemented sands.

CYCLIC BEHAVIOR 109

u

b ' v =>

:::> L

t-a: a: u.J a: ::::i U"J U"J u.J a: a.. u.J a: 0 a..

1. 0

0.8

0.6

0.4

0.2

0.0 0.0

KEI STRESS I SYMBCJL RAT !Cl

0.250 x 0.300 ~

0.350 12:1

0.400 <'>

1 i.: CEMENTED - - - Equation 7 .1 --Equation 7.2

,:;,:······.::···!;:/""\__RANGE OF VALUES FCTR - UNCEMENTEO SANO

!LEE t. ALBEISA, 19751

0.2 0.4 0.6 0.8 1. 0

CYCLIC RATIO,

Figure 7-11: Pore pressure ratio vs. cyclic ratio data for cemented sand compared to empirically developed curves.

CYCLIC BEHAVIOR 110

7.4 EFFECT OF A WEAK LENS ON LIQUEFACTION RESISTANCE

The liquefaction resistance curve for the layered sample is compared in

Figure 7-12 to the curves for the other materials of this investigation.

As discussed in Chapter 4, the nonhomogeneous samples were created by

layering homogeneous materials of the same density as used in the homo-

geneous static and cyclic tests. In this case, a 1 centimeter layer of

a 1 percent cement mix is sandwiched between two, 7 centimeter layers of

2 percent mix sand.

There are two features of the liquefaction curve for nonhomogeneous

cementation (Figure 7-12) that warrant special attention. First, and not

surprisingly, the curve for this material falls between the curves for

the homogeneous, 1% and 2% samples. This is significant in that the

nonhomogeneous samples constitute a layering of those two materials. This

demonstrates that weak lenses certainly lower the liquefaction resistance

of stronger masses, but do not necessarily constitute a limiting condition

"weak link" that fully determines the cyclic shear resistance of the de-

posit. Secondly, it is interesting to note that the liquefaction re-

sistance curve for the layered samples lies closest to the 1% curve at

higher stress ratios, while at lower stress ratios the curve seems to veer

toward the 2% curve. This suggests that the weak lens has less influence

on the total mass at low shear stress levels, but, shows the reverse trend

at high shear stress levels.

CYCLIC BEHAVIOR 111

0.60

0.55

0.50 a: Cf)

• 0.45 0

~ 0. 40 a: ~ o. 35 I.LI a: ~ 0. 30 a: ~ 0. 25 :c Cf)

u 0. 20 ..... .....I u o. 15 >-u

0. 10.

a.as 0.00

1 2 5 10 20 so

AVG. DENSITY • JS. 70 KN/M3

LAYERED SAMPLES INllIRL LIQUEFRClJON

21. CEMENT CDNTENT CJ NDNHDMDGENEDUS + 1 'l. CEMENT CDNTENT ~

ND LICUEFRCTIDN. l'l. )::(

UNCEMENTEO

I 1

100 200 500 1000 NUMBER ~F STRESS CICLES, N

Figure 7·12: Cyclic shear resistance curves for nonhomogeneous samples compared to various cementation configurations.

CYCLIC BEHAVIOR 112

This may be a function of strain as indicated in Section 7.5, where high

strains were seen to cnntrol the rate of pore pressure generation in cy-

clically loaded samples. This can be interpreted as the cementstion ex-

erting its character more strongly st increased strains.

During cyclic testing st low stress ratios, the stronger masses were no-

ticed to develop appreciable strains st a proportionately earlier stage

of loading than st higher stress ratios. At higher stress ratios, greater

strains were noted in the central, weaker lens than in the stronger mass,

even up to the point of initial liquefaction. This would result in the

weak lens exhibiting more of its cemented characteristics than the

stronger material, leading to greater control over pore pressure gener-

ation. Ultimately, this means that the weak lenses have a stronger in-

fluence upon liquef sction resistance st higher stress ratios.

It is significant to note from Figure 7-12 that the weak lens consistently

predominates the liquefaction resistance st events lasting up to 20 cy-

cles, which constitutes the range of duration for most reported seismic

events (Silver and Park, 1975). It is not known whether these observa-

tions hold true for variations in the relative levels of cementstion

within the samples, and the relative thicknesses of the layers.

Since there are a wide variety of natural cementing agents, it is diffi-

cult to quantify this in terms of percent cement as can be done for the

artificially cemented sands. It is more appropriate to refer to levels

of cementstion in terms of unconfined compressive strengths. Recalling

CYCLIC BEHAVIOR 113

that it was shown, during the static testing phase of this research, that

the presence of a weak lens in a stronger mass is also reflected in this

static strength measurement, the unconfined compressive strength may be

used to compare homogeneously cemented samples to those with inconsist-

encies. Figure 7-13 plots the unconfined compressive strength versus the

cyclic shear stress ratio necessary to induce liquefaction in a given

number of cycles (10, 50, and 100).

The unconfined compressive strengths presented in Table 6-2 are

representitive of the effective cementation levels and determine the

abscissae of the data points in Figure 7-13. The cyclic shear resistance

curves shown in Figure 7-12 provide the basis for the ordinates. For

instance, the 2% cemented sand has an unconfined compressive strength of

327 KN/M1 • Examination of the proper curve in Figure 7-12, which was

developed for initial liquefaction, shows that a stress ratio of 0.375

is required to cause liquefaction in exactly 100 cycles. Similar points

are plotted for the uncemented and nonhomogeneous samples to develop the

100 cycle resistance curve.

The trend of the curves in Figure 7-13, which is asymptotic with respect

to stress ratio, is inconsistent with observed behavior; high levels of

cementation, or unconfined compressive strength, have been shown to pre-

clude liquefaction in laboratory testing (Dupas and Pecker, 1979). In a

qualitative sense, however, Figure 7-13 demonstrates that the cyclic re-

sponse of undrained, nonhomogeneously cemented soils may be distinguished

by static strength properties.

CYCLIC BEHAVIOR 114

It is apparent that static tests, particularly carefully performed in-

situ procedures on undisturbed soils, can provide enough information to

reflect the liquefaction resistance of nonhomogeneously cemented soils.

The controlling factor in these situations would seem to be compitability

between the testing device and the discontinuities in the soil.

Insofar as pore pressure development is concerned, it is evident form

Figures 7-14 and 7-15 that observations made about cemented sands, gen-

erally hold true for nonhomogeneously cemented soils. These pore pressure

ratio and strain ratio plots demonstrate the same stress ratio and axial

strain relationships seen with the homogeneous samples; at low stress

ratios and low strain levels, the cemented sand behaves similarly to un-

cemented sand. Consequently, generated pore pressures in

nonhomogeneously cemented sands may be predicted by judicious use of

Equations 7.1 through 7.3.

CYCLIC BEHAVIOR 115

0.6

::<J z er.. 0 ;::> 1-1 < E-< 0.4 u C,.) N=SO < c ~ N=lOO E-< ~

:::i c O" H 1-1

~ ..J IX. ....:i < Cl.) H 0.2 Cl.) ~ ::<J ,_.; i::r:: z E-< H :n

I 0.0 LO----.l..----1~00 ____ .i.._ ___ 20~0----"'-----30~0----"-----400

UNCONFINED COHPRESSIVE S'i'REHGTH (KN/H2)

Figure 7-13: UCS vs. stress ratio to liquefaction.

CYCLIC BEHAVIOR 116

u

b .......

Q) :::J

::I L

...... t-a: a: IJ.J a: ::::> (J') (J') IJ.J a: a.. IJ.J a: 0 a..

1. a

a.8

a.6

a.4

a.2

a.a a.a

KEY STRESS SYMBCIL RRT !Cl 0.300 C)

0.325 x 0.350 .:!>

0.400 ~

0.450 ~

NCJNHCJMCJGENECJUS

.::·· .:::ii''".,/';!ii'''l\__ RANGE CIF VALUES FCIR

. UNCEMENTED SAND !LEE ~ ALBE I SA, 19751

a.2 a.4 a.6 a.8 C'YCL IC RAT rn,

Figure 7-14: Pore pressure ratio vs. cyclic ratio (nonhomogeneous).

i. a

CYCLIC BEHAVIOR 117

.,. -w

......... c: w

II

"" L

. 0 ...... I-a: cc z ...... a: cc I-U')

1. 0

0.8

0.6

0.4

0.2

0.0 0.0

KE I STRESS SYMBCIL RAT!CI

0.300 C)

0.400 ~

0.450 ~

NONHOMCJGENECIUS

0.2 0. Lj 0.6 0.8

CICL IC RAT rn,

. Figure 7·15: Strain ratio vs. cyclic ratio (nonhomogeneous).

1. 0

CYCLIC BEHAVIOR 118 .

8.0 SUMMARY AND CONCLUSIONS

Cemented sands are prevalent throughout the world. While they are often

able to stand in slopes approaching vertical, failure of saturated de-

posits as a result of seismic activity can be catastrophic. Cementation

has been shown to increase the peak strength, stiffness and liquefaction

resistance of sands. Much of the work in this area has been done with

natural materials wherein it is difficult to isolate the parameters con-

tributing to static and cyclic strength. The present work serves to al-

leviate this condition by providing static and cyclic test data from 35

tests on carefully controlled, artificially prepared samples.

The focus of this work centered on three areas that had yet to be ad-

dressed satisfactorally by previous research:

1. What is the effect of nonhomogeneity on the liquefaction re-

sistance of lightly cemented sands?

2. How does cementation affect the volume change characteristics

of statically loaded samples?

3. Is it possible to predict the pore pressure generation of un-

drained, weakly cemented sands subjected to cyclic loading?

SUMMARY and CONCLUSIONS 119

A degree of preliminary work was necessary prior to beginning the actual

tests. An efficient sample preparation technique was developed, based

on improvement of a method devised by Rad and Clough (1982). The new

method is made possible by a mated sand rainer and mold device which is

easy to use and allows construction of homogeneous samples at controlled,

consistent, densities. It was also necessary to develop a means of

preparing layered samples to simulate cemented sand deposits with weak

lenses. This was done by stacking partially cured, homogeneous, samples

of cemented sand at two levels of cementation; essentially, a one cen-

timeter 'lens' of 1% cemented sand was embedded into a 15 centimeter

tall, 2% cemented sample. The method insures accurate control of rela-

tive thickness and degree of cementation of the respective layers.

To achieve complete saturation of the cemented material, a vacuum satu-

ration device was constructed, primarily based on the original version

described by Rad and Clough (1984).

A state-of-the-art cyclic triaxial testing apparatus was assembled

around a new MTS 445 controller. All controller components were tested

and calibrated, and the Honeywell Oscillograph , used for data retrieval,

was made compatible with the ranges of load, deformation, and pore

pressure expected from the respective transducers during normal testing.

For the consolidated, drained, static triaxial tests, 2% cemented sam-

ples were constructed to densities of 15. 00, 15. 45, and 15. 70 KN/Ml.

Layered samples at a density of 15. 70 KN/Ml were tested in the same


manner. Undrained cyclic triaxial tests with pore pressure measurement

were performed on uncemented sand, 1% and 2% cemented sand, 1L.1d layered,

or nonhomogeneous, samples. The average density of all the samples

tested in cyclic fashion was 15.70 KN/M 3 •

The static testing program yielded the following observations:

1. The addition of different quantities of Portland cement to sand

samples introduces structural differences upon curing. Conse-

quently, the use of the relative density concept does not seem

applicable to these materials. For this investigation, the

writer has chosen to distinguish density by dry unit weight.

2. A weak lens is seen to lower both peak strength and stiffness

of a stronger mass. This is due primarily to a reduction in

the apparent cohesion of the composite material.

3. The absolute magnitude of volumetric strain developed at fail-

ure seems to be independent of the level of cementation.

4. The rate of volumetric expansion is related to the amount of

cementation.

5. Casagrande's critical void ratio concept, in its present form,

is not applicable to cemented sands.


The undrained cyclic triaxial compression data lead to the following

conclusions:

1. Monterey #0/30 sand has a higher liquefaction resistance than

does Monterey #0 sand.

2. At low stress ratios, when a large number of cycles to

liquefaction are required, the pore pressure generation of ce-

mented sands is similar to that of uncemented sands.

3. As the stress ratio increases, the shape of the cemented pore

pressure development curve exhibits characteristics different

than that of uncemented sand. The shape of this curve has been

described and can be used in prediction for pore pressure de-

velopment in cemented sands.

4. The rate of pore pressure development seems to be controlled,

in part, by the magnitude of cyclic axial strain. Similarly,

the effects of cementation on pore pressure generation actually

becomes more evident after sample strain has destroyed some of

the sand-cement bonds.

5. A weak lens serves to lower the ability of a stronger mass to

sustain dynamic loads. This effect is seen to decrease with

decreasing stress ratio.


6. If appropriate static in-situ tests are carefully performed,

the results are likely to reflect increased liquefaction re-

sistance due to cementation.

The writer suggests that future research efforts in the area of lightly

cemented sands include:

1. Testing of nonhomogeneous samples constructed by other methods,

such as continuous raining, without the possible discontinui-

ties introduced at the layer boundaries by the present tech-

nique.

2. A parametric study of layered samples focusing on the effects

of relative layer size and cementation level. This should in-

clude samples with an uncemented lens.

3. Tests on samples with different types of cementation, ideally

with cementing agents with less tendency to crystalize than

Portland cement.

4. Additional testing of reconstituted, cemented samples to de-

termine whether these materials are useful as indicators of

in-situ liquefaction resistance.

S. Further investigation into the concept of using field tests,

such as the self boring pressuremeter, to measure behavior


characteristics of cemented sand, that can be related to

liquefaction resistance.


APPENDIX A. EQUIPMENT IDENTIFICATION

Appendix A. EQUIPMENT IDENTIFICATION 125

Item

Load Frame

Pore Pressure Panel and Triaxial Cell

Load Cell

Pressure Transducer

Differential Pressure Transducer

Table A-la: Equipment Information

Model

RE-SS-2400E

SM-1000

EPX-lOU-100

DP15-50

Serial Number

VPI83941

VPI85879

A36761

2R3R-Dl3-l

648 59

Operating Range

1000 lbs.

0-100 psi

0-50 psi

Manufacturer/Supplier

Budd Riley Research Engineering 2640 Dundee Road San Pablo, CA 94806 (415) 223- 4798

Marshall Silver Geotechnical Equipment Corporation 151 Belle Avenue Highland Park, Illinois 60035 (312) 433-0014

Interface, Inc. 7401 E. Butherus Dr. Scottsdale, Arizona 85260 (602) 948-5555

Entran Devices, Inc. 10 Washington Avenue Fairfield, New Jersey 07006 (201) 227-1002

Validyne Engineering Company 8626 Wilber Avenue Northridge, California 91324 (800) 423-5851

Item

MTS System:

controller

valve driver

auto mode switching servo

D.C. conditioner

A.C. conditioner

limit detector

control unit

digital function generator

Visicorder

Table A-lb: Equipment Information (continued)

Serial Model Number

810R 959.93

445 .11 251

440.14 2918

440.17 264

440.21 5787

440.22 2520

440.41 672

436 .11 596

410.31 2643

1508C 0806A684

Operating Range Manufacturer/Supplier

MTS Systems Corporation Box 24012 Minneapolis, Minnesota 55424 (612) 937-4000

Honeywell Test Instruments P.O. Box 5227 4800 E. Dry Creek Denver, Colorado (303) 773-4584

Division

Road 80217

APPENDIX B. USE OF THE HTS CYCLIC TESTING APPARATUS

This appendix describes the procedure used to perform stress controlled

cyclic triaxial tests with the equipment available to the researcher

during the experimental phase of this research project. A list of all

equipment components, with pertinent information, is included in Appen-

dix A. It is suggested that the reader become adequately familiar with

the appropriate manufacturer 1 s literature before operating equipment.

Damage to the more sensitive apparati or bodily injury may otherwise

result.

The following procedure assumes that the triaxial cell, with sample, is

prepared for testing; and that the MTS 445 controller, Honeywell

Visicorder, and differential pressure transducer have been calibrated.

The reader is referred to the VP! MTS User's Guide (Milstone, 1985) for

calibration procedures.

B.1 MTS STRESS CONTROLLED CYCLIC !BIAXIAL TESTING PROCEDURE

1. Hydraulics off. Clear D/A on 440.17 auto mode switching servo mod-

ule.

(This resets error count to zero.)

Enter STROKE mode on 445 front panel, activating channel 1 (and its

indicator light on the 440.37 processor controller module).

Appendix B. Use of the MTS Cyclic Testing Apparatus 128

processor controller. Pressing the STROKE button successively will

switch the active c~annel.

2. On 440.37 processor controller: Select set point, span 1 for channel

1. Select set point, span 2 for channel 2.

(LOAD mode will be controlled by channel 2. This procedure commits

the span control dials on the 445 front panel to the respective

program modes, and activates the set point control dial for both

modes.)

3. Exercise the servo valves and the actuator:

a. On 440. 17 switching servo module: Select set point on readout

select.

b. On 445 front panel: Monitor set point on meter board by

switching to SERVO. It is more accurate to monitor settings with

a voltmeter. This can be done by patching to a voltmeter from

the output jacks that are directly below the sweep meter.

c. Adjust set point to 0.000 using set point knob at COMMAND area

of 445 controller. Apply low pressure while simultaneously

pressing interlock reset button. Hold interlock reset button

until piston has stabilized in neutral position. Both + and -

balance indicator lights will be out at this point.


d. Adjust span 1 to approximately 2 volts to control stroke length.

e. Apply high pressure hydraulics.

f. On 410 function generator: Choose invert-sine wave; set fre-

quency of RATEl to 1 cycle per second.

g. Begin program by pressing RUN button on 436 control unit. This

will commence the piston to cycling the chosen distance (span)

about the set point.

h. Span may be adjusted, if desired, while program is running.

4. This warmup time (1/2 to 1 hr.) may be used to saturate sample which

has not yet been placed in load frame.

Stop program by pressing STOP button on 436 control unit.

5. Switch to LOAD mode:

a. Set range of load cell conditioner and apply limit detect to

protect load cell from overload:

• Choose range 1 - 4 on 440.21 load cell conditioner module.

This will effectively increase the sensitivity of load cell

output by factors of 1, 2, 5, and 10 respectively. (ex.:


For 100 lb. load cell at range setting 3, lOV output re-

presents 20 lbs.)

• Set upper and lower (tension and compression) limit detect

values for XDCRl on 440.41B module. Limits are chosen based

on load cell capacity, XDCRl calibration range, and antic-

ipated maximum loads.

• Flip XDCRl toggle switch on 440.41B module to INTLK. This

will cause system to interlock (shut down) if chosen limit

is exceeded, protecting load cell from overload. Look at

COMMAND area of 445 front panel. XDCRl limit detect lights

will glow green if interlocking limit option has been prop-

erly activated.

b. Turn hydraulics off with 436 control unit. Switch to LOAD mode

and channel 2 by pressing LOAD button on 445 front panel.

c. Zero the load cell feed back:

• Monitor XDCRl (load cell feedback) with voltmeter patched

to output jacks below sweep meter.

• While there is no load applied to the load cell, zero the

feedback by adjusting the balance (ZERO dial) of the load

cell 440.21 D.C. conditioner. (Rightmost module behind 445

front panel.)


6. Fit triaxial cell onto MTS load frame:

a. Apply low pressure hydraulics. Interlock should not have been

activated since there is no error between the load cell feedback

and the set point which are both 0.000.

b. Applying a compression load to the load cell, by hand, will force

the piston to move down as the feedback system attempts to return

the measured load to 0.000.

c. Set triaxial cell on piston platen, screwing wing-bolts in

place. The bolts should be left loose until step-g, after the

cell has been moved into its final position.

d. Applying a tension load to the load cell, by hand, will raise

the piston with the cell into contact with the threaded rod at

the load cell. Keep fingers out of dangerous places.

e. Tap cell into concentric position with load rod in contact with

coupling barrel. Contact is maintained by the tensile force

applied to the load cell.

f. When triaxial cell is concentric with load cell, screw coupling

barrel a distance of about 4 threads onto threaded portion of

load rod (maintaining tension force until threads are engaged.)

Secure top and bottom of coupling barrel with lock nuts.


g. Tighten wing-bolts to secure triaxial cell to MTS piston.

7. Isotropically consolidate sample:

a. Set compensating axial load to affect isotropic stress condi·

tions:

1) Loading rod remains locked in position.

2) Load has been determined experimentally for each consol·

idation pressure, or it is calculated as:

(cell press.*load rod area) - wgt.of(rod+platen)

3) While monitoring XDCRl, adjust set point to apply compen-

sating load. (Counterclockwise adjustment induces com·

pression; clockwise adjustment induces tension.)

b. Consolidate sample:

1) Record initial burette reading.

2) Monitor XDCR3 (LVDT feedback) and record initial sample

height.

3) Close valve to burette such that sample is undrained.


4) Increase cell pressure to chosen consolidation pressure.

5) Unlock piston to apply compensating axial load.

6) Open valve to commence consolidation.

7) Following consolidation, record final burette reading and

final XDCR3 reading. Volume change and axial strain due to

consolidation can then be calculated by applying the appro-

priate calibration factors.

8. Prepare Honeywell Visicorder:

• Aim galvanometers to appropriate zero locations.

• Set time gap and paper speed.

(Time gap of 1.0 seconds and paper speed of Smm/second are con-

venient.)

9. Set amplitude of loading program (deviatoric load):

a. Amplitude of deviatoric load is calculated from chosen stress

ratio:

Dev.Str.=SR*2*init.eff.consol.press.*sample area

where: sample area has been corrected for consolidation.

b. Set deviatoric load by adjusting span 2 to proper dial setting.


10. Verify deviatoric load:

a. Lock load rod to the triaxial cell.

b. Monitor XDCRl by connecting an oscillocope to the output jacks

on the meter board.

Start paper advance of Honeywell Visicorder for additional mon-

itoring source. This output is convenient as the hard copy is

easily scaled for higher accuracy.

c. Begin program by hitting RUN button on the 436 controller. This

will generate feedback from the load cell that can be monitored

at the oscilloscope and Visicorder, while adjusting the span to

obtain the correct deviatoric load. This procedure also warms

up the feedback system and allows the loading system to seat

itself, without disturbing the sample.

d. Stop program.

11. Liquefy sample:

a. Unlock load rod.

b. Close valve to burette such that sample is undrained.

c. Start paper advance of Honeywell Visicorder.


d. Hit RUN. Watch sample and Visicorder for signs of liqeufaction.

e. After sample has liquefied:

• Stop program.

• Open valve to burette allowing excess pore pressures to

dissipate. (This will indicate if there was any zero shift

at the Visicorder.)

• Stop Visicorder paper advance.

12. Remove sample from load frame:

a. Close valves to drain lines at pressure panel and at sample; then

remove cell pressure line and drainage lines from triaxial cell.

b. Monitor XDCRl and return to zero by adjusting set point clock-

wise.

c. Loosen lock nuts and back off coupling barrel from load rod.

d. Apply compression load to load cell, by hand, forcing actuator

to lower the cell.

e. Switch hydraulics off. Remove anchor bolts and remove cell from

load frame. (If convenient, it is helpful to empty the cell of

water before lifting it from MTS frame. )


REFERENCES

Bishop, A. W. and Henkel D. J. , Measurement of Soil Pr2perties in the Triaxial Test. Second Edition, Edward Arnold Publishers, Ltd. , London, England, 1962.

Castro, G., "Liquefaction and Cyclic Mobility of Saturated Sands, 11

Journal of the Geotechnical Engineering Division, ASCE, June, 1975, pp. 551-569.

Clark, R. G. , "The Use of MTS Equipment in Liquefaction Studies," Master of Engineering Report, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, May, 1983.

Clough, G. W. and Silver, M. L. , coeditors, "A Report on the Workshop on Research Needs in Experimental Soil Engineering," Virginia Polytechnic Institute and State University, Blacksburg, Virginia, August 22-25, 1983.

Clough, G. W., Sitar, N., Bachus, R. C. and Rad, N. S., "Cemented Sands Under Static Loading, 11 Journal of the Geotechnical Engineering Di-vision, ASCE, Vol. 107, No. GT6, June, 1981, pp. 799-817.

Committee on Soil Dynamics, "Definition of Terms Related to Liquefaction," Journal of the Geotechnical Endneering Division, ASCE, Vol. 104, No. GT9, September, 1978, pp.1197-1200.

DeAlba, P. , Chan, C. K. , and Seed H. B. , "Determination of Soil Liquefaction Characteristics by Large-Scale Laboratory Tests," k port No· EERC 75-14, Earthquake Engineering Research Center, Uni-versity of California, Berkeley, California, May, 1975.

Dobry, R., Powell, D. J,, Yokel, F. Y. and Ladd, R. S., "Liquefaction Potential of Saturated Sands, Stiffness Method," Proceedings, 7th World Conference on Earthquake Engineering, Vol. 3, Turkey.

Eid, W., Doctoral Dissertation in Progress, Virginia Polytechnic Insti-tute and State University, Blacksburg, Virginia, June, 1984.

Frydman, S. et al. , "Liquefaction of Cemented Sands," Journal of the Geotechnical Engineering Division, ASCE, Vol. 106, No. GT3, March, 1980, pp. 275-297.

Ladd, R. S. , "Specimen Preparation and Cyclic Stability of Sands," Journal of the Geotechnical Endneering Divis ion, ASCE, Vol. 103, No. GT7, June, 1977, pp.535-547.

REFERENCES 137

Lee, K. L. and Albeisa, A. , "Earthquake Induced Settlements in Saturated Sands," Journal of Soil Mechanics and Foundation Division, ASCE, Vol. 100, No. GT4, April, 1974.

Lowe, J. and Johnson, T. C. , "Use of Backpressure to Increase Degree of Saturation of Triaxial Test Specimens," Presented at the 1960 ASCE Research Conference on Shear Strength of Cohesive Soils, Boulder, Colorado, 1960, pp. 819-836.

Martin, G. R. , Finn, W. D. L. and Seed, H.B. , "Fundamentals of Liquefaction Under Cyclic Loading," Journal of the Geotechnical Engineering Di-vision, ASCE, Vol. 101, No. GT5, May, 1975, pp. 423-438.

Mulilis, J. P., Seed, H. B., Chan, C. K., Mitchell, J. K. and Arulanandan, K. , "Effects of Sample Preparation on Sand Liquefaction," Journal of the Geotechnical Engineering Division, Vol. 103, No. GT2, February, 1977, pp. 91-108.

Peck, R. B. , "Liquefaction Potential: Science Versus Practice" ,Journal of the Geotechnical Engineering Division, ASCE, Vol. 101, GTll, No-vember, 1975, pp. 393-397.

Rad, N. S. and Clough, G. W. , "The Influence of Cementation on the Static and Dynamic Behavior of Sands," Report No. 59, The John A. Blume Center, Stanford University, Palo Alto, California, Prepared for the United States Geologic Survey, Offce of Earthquake Studies, December, 1982.

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