Subgrades and Subbases for Concrete subbase, subbase, subgrade, unstabilized subbase, volume stability

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  • AMERICAN CONCRETE PAVEMENT ASSOCIATION

    Subgrades and Subbases for Concrete Pavements

    ENGINEERING BULLETIN

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    AMERICAN CONCRETE PAVEMENT ASSOCIATION

    This publication is intended SOLELY for use by PROFESSIONAL PERSONNEL who are competent to evaluate the significance and limitations of the information provided herein, and who will accept total responsibility for the application of this information. The American Concrete Pavement Asso- ciation DISCLAIMS any and all RESPONSIBILITY and LIABILITY for the accuracy of and the application of the information contained in this publication to the full extent permitted by law.

    American Concrete Pavement Association 5420 Old Orchard Rd., Suite A100 Skokie, IL 60077-1059 www.pavement.com

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  • Subgrades and Subbases for Concrete Pavements

    ACPA is the premier national association representing concrete pavement contractors, cement companies, equipment and materials manufacturers and suppliers. We are organized to address common needs, solve other problems, and accomplish goals related to research, promotion, and advancing best practices for design and construction of concrete pavements.

    American Concrete Pavement Association 5420 Old Orchard Rd., Suite A100 Skokie, IL 60077-1059 (847) 966-ACPA www.pavement.com

  • Subgrades and Subbases for Concrete Pavements

    ii

    Keywords: AASHTO, ASTM, asphalt-treated, cement-treated, cement-stabilized, chemical modification, concrete pavement, cross- hauling, cut-fill transition, daylighted, drainable subbase, econocrete, edge drainage, expansive soil, faulting, free-draining, frost heave, frost-susceptible soil, granular subbase, lean concrete, pavement structure, permeable subbase, pumping, reclaimed asphalt pavement (RAP), recycled concrete, separator, sieve analysis, soil, soil classification system, spring subgrade softening, stabilized subbase, subbase, subgrade, unstabilized subbase, volume stability.

    Abstract: This engineering bulletin provides the necessary background information for the proper selection and application of subbases and the appropriate consideration of subgrade variables for concrete pavements used for streets, roads and highways. It emphasizes the major objective of obtaining long-lasting uniform support for a concrete pavement. Subgrade soil material classifica- tion and problems (expansion, heaving, etc.) are discussed in detail along with many various options for stabilized and unstabilized subbases, and the materials that they are composed of. Multiple reasons for avoiding the use of permeable subbases (a.k.a. drainable or open-graded subbases) also are presented.

    EB204P

    © 2007 American Concrete Pavement Association

    All rights reserved. No part of this book may be reproduced in any form without permission in writing from the publisher, except by a reviewer who wishes to quote brief passages in a review written for inclusion in a magazine or newspaper.

    ISBN 978-0-9800251-0-1

    This publication is intended SOLELY for use by PROFES- SIONAL PERSONNEL who are competent to evaluate the significance and limitations of the information provided herein, and who will accept total responsibility for the appli- cation of this information. The American Concrete Pavement Association DISCLAIMS any and all RESPONSIBILITY and LIABILITY for the accuracy of and the application of the information contained in this publication to the full extent permitted by law.

  • iii

    Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii Executive Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix Chapter 1 – Introduction and Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Chapter 2 – Design Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Uniform Support. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

    Influence of Foundation Strength on Concrete Pavement Thickness . . . . . . . . . . . . . . . . . . . . . . 6

    Influence of Foundation Stiffness on Stresses and Strains in Concrete Pavement Slabs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

    Pavement System Drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

    Sources of Moisture in a Pavement Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

    Free-Draining Subbases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

    Edge Drainage Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

    Edge Drain Piping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

    Daylighting the Subbase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

    Separators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

    Chapter 3 – Subgrades . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Soil Basics for Pavement Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

    Moisture Content and Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

    Soil Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

    Moisture Equivalent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

    Soil Moisture Suction (Capillary Action). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

    Plastic Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

    Nonplastic Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

    Load Bearing Capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

    Volume Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

    Classification Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

    AASHTO Soil Classification System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

    ASTM (Unified) Soil Classification System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

    Soil Texture Method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

    Subgrade Strength and Working Platform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

    Obtaining Uniform Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

    Expansive Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

    Compaction and Moisture Control of Expansive Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

    Table of Contents

  • Subgrades and Subbases for Concrete Pavements

    iv

    Selective Grading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

    Chemical Modification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

    Material Selection and Dosage Rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

    Constructing Modified/Stabilized Subgrades . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

    Special Methods for Controlling Expansive Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

    Frost Action. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

    Frost Heave. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

    Frost-Susceptible Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

    Spring Subgrade Softening. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

    Control of Frost Heave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

    Grade and Water Table Elevation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .