Craig's Soil Mechanics 7th Edition
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Craig's Soil Mechanics 7th Edition

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Craig’s Soil Mechanics

Craig’s Soil Mechanics

Seventh edition

R.F. Craig
Formerly

Department of Civil Engineering

University of Dundee UK

First published 1974
by E & FN Spon, an imprint of Chapman & Hall
Second edition 1978
Third edition 1983
Fourth edition 1987
Fifth edition 1992
Sixth edition 1997
Seventh edition 2004

11 New Fetter Lane, London EC4P 4EE

Simultaneously published in the USA and Canada
by Spon Press
29 West 35th Street, New York, NY 10001

Spon Press is an imprint of the Taylor & Francis Group

ª 1974, 1978, 1983, 1987, 1992, 1997, 2004 R.F. Craig

All rights reserved. No part of this book may be reprinted or reproduced or
utilised in any form or by any electronic, mechanical, or other means, now known
or hereafter invented, including photocopying and recording, or in any information
storage or retrieval system, without permission in writing from the publishers.

British Library Cataloguing in Publication Data
A catalogue record for this book is available
from the British Library

Library of Congress Cataloging in Publication Data
Craig, R.F. (Robert F.)

[Soil mechanics]
Craig’s soil mechanics / R.F. Craig. — 7th ed.

p. cm.
Second ed.: Soil mechanics / R.F. Craig. Van Nostrand Reinhold, 1978.
Includes bibliographical references and index.
ISBN 0–415–32702–4 (hb.: alk. paper) — ISBN 0–415–32703–2 (pbk.: alk.
paper)
1. Soil mechanics. I. Title: Soil mechanics. II. Craig, R.F. (Robert F.) Soil
mechanics. III. Title.

TA710.C685 2004
624.105136—dc22

2003061302

ISBN 0–415–32702–4 (hbk)
ISBN 0–415–32703–2 (pbk)

This edition published in the Taylor & Francis e-Library, 2005.

ISBN 0-203-49410-5 Master e-book ISBN

ISBN 0-203-57441-9 (Adobe eReader Format)

“To purchase your own copy of this or any of Taylor & Francis or Routledge’s
collection of thousands of eBooks please go to www.eBookstore.tandf.co.uk.”

Contents

Preface viii

1 Basic characteristics of soils 1
1.1 The nature of soils 1
1.2 Particle size analysis 6
1.3 Plasticity of fine soils 7
1.4 Soil description and classification 9
1.5 Phase relationships 17
1.6 Soil compaction 21
Problems 28
References 29

2 Seepage 30
2.1 Soil water 30
2.2 Permeability 31
2.3 Seepage theory 37
2.4 Flow nets 42
2.5 Anisotropic soil conditions 49
2.6 Non-homogeneous soil conditions 52
2.7 Transfer condition 53
2.8 Seepage through embankment dams 55
2.9 Grouting 66
2.10 Frost heave 66
Problems 67
References 70

3 Effective stress 71
3.1 Introduction 71
3.2 The principle of effective stress 71
3.3 Response of effective stress to a change in total stress 74
3.4 Partially saturated soils 79
3.5 Influence of seepage on effective stress 80
Problems 88
References 90

4 Shear strength 91
4.1 Shear failure 91
4.2 Shear strength tests 94
4.3 Shear strength of sands 102
4.4 Shear strength of saturated clays 106
4.5 The critical-state concept 118
4.6 Residual strength 125
4.7 Pore pressure coefficients 127
Problems 133
References 135

5 Stresses and displacements 136
5.1 Elasticity and plasticity 136
5.2 Stresses from elastic theory 144
5.3 Displacements from elastic theory 155
Problems 159
References 160

6 Lateral earth pressure 161
6.1 Introduction 161
6.2 Rankine’s theory of earth pressure 162
6.3 Coulomb’s theory of earth pressure 176
6.4 Application of earth pressure theory to retaining walls 184
6.5 Design of earth-retaining structures 185
6.6 Gravity walls 187
6.7 Embedded walls 195
6.8 Braced excavations 212
6.9 Diaphragm walls 215
6.10 Reinforced soil 217
Problems 221
References 225

7 Consolidation theory 227
7.1 Introduction 227
7.2 The oedometer test 227
7.3 Consolidation settlement: one-dimensional

method 235
7.4 Settlement by the Skempton–Bjerrum method 237
7.5 The stress path method 243
7.6 Degree of consolidation 244
7.7 Terzaghi’s theory of one-dimensional consolidation 245
7.8 Determination of coefficient of consolidation 252
7.9 Correction for construction period 260
7.10 Numerical solution 265
7.11 Vertical drains 268
Problems 274
References 276

vi Contents

8 Bearing capacity 277
8.1 Foundation design 277
8.2 Ultimate bearing capacity 281
8.3 Allowable bearing capacity of clays 293
8.4 Allowable bearing capacity of sands 294
8.5 Bearing capacity of piles 311
8.6 Ground improvement techniques 332
8.7 Excavations 336
8.8 Ground anchors 339
Problems 342
References 344

9 Stability of slopes 347
9.1 Introduction 347
9.2 Analysis for the case of �u ¼ 0 348
9.3 The method of slices 351
9.4 Analysis of a plane translational slip 357
9.5 General methods of analysis 360
9.6 End-of-construction and long-term stability 362
9.7 Embankment dams 364
Problems 369
References 371

10 Ground investigation 373
10.1 Introduction 373
10.2 Methods of investigation 374
10.3 Sampling 381
10.4 Borehole logs 388
10.5 Geophysical methods 388
10.6 Ground contamination 393
References 394

11 Case studies 395
11.1 Introduction 395
11.2 Field instrumentation 396
11.3 The observational method 407
11.4 Illustrative cases 409
References 434

Principal symbols 436
Answers to problems 440
Index 443

Contents vii

Preface

This book is intended primarily to serve the needs of the undergraduate civil engineer-
ing student and aims at the clear explanation, in adequate depth, of the fundamental
principles of soil mechanics. The understanding of these principles is considered to be
an essential foundation upon which future practical experience in geotechnical engin-
eering can be built. The choice of material involves an element of personal opinion but
the contents of this book should cover the requirements of most undergraduate
courses to honours level as well as parts of some Masters courses.
It is assumed that the reader has no prior knowledge of the subject but has a good

understanding of basic mechanics. The book includes a comprehensive range of
worked examples and problems set for solution by the student to consolidate under-
standing of the fundamental principles and illustrate their application in simple
practical situations. Both the traditional and limit state methods of design are included
and some of the concepts of geotechnical engineering are introduced. The different
types of field instrumentation are described and a number of case studies are included
in which the differences between prediction and performance are discussed. References
are included as an aid to the more advanced study of any particular topic. It is
intended that the book will serve also as a useful source of reference for the practising
engineer.
The author wishes to record his thanks to the various publishers, organizations and

individuals who have given permission for the use of figures and tables of data, and to
acknowledge his dependence on those authors whose works provided sources of
material. Extracts from BS 8004: 1986 (Code of Practice for Foundations) and BS
5930: 1999 (Code of Practice for Site Investigations) are reproduced by permission of
BSI. Complete copies of these codes can be obtained from BSI, Linford Wood, Milton
Keynes, MK14 6LE.

Robert F. Craig
Dundee

March 2003

The unit for stress and pressure used in this book is kN/m2 (kilonewton per square
metre) or, where appropriate, MN/m2 (meganewton per square metre). In SI the
special name for the unit of stress or pressure is the pascal (Pa) equal to 1N/m2

(newton per square metre). Thus:

1 kN/m2 ¼ 1 kPa (kilopascal)
1MN/m2 ¼ 1MPa (megapascal)

Chapter 1

Basic characteristics of soils

1.1 THE NATURE OF SOILS

To the civil engineer, soil is any uncemented or weakly cemented accumulation of
mineral particles formed by the weathering of rocks, the void space between the
particles containing water and/or air. Weak cementation can be due to carbonates
or oxides precipitated between the particles or due to organic