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Geotechnical Engineering Established as a standard textbook for students, this new edition of Geotechnical Engineering provides a solid grounding in the mechanics of soils and soil-structure interaction. Renato Lancellotta gives a clear presentation of the fundamental principles of soil mechanics a...

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Geotechnical Engineering

Established as a standard textbook for students, this new edition of Geotechnical Engineering provides a solid grounding in the mechanics of soils and soil-structure interaction. Renato Lancellotta gives a clear presentation of the fundamental principles of soil mechanics and demonstrates how these principles are applied in practice to engineering problems and geotechnical design. This is supported by numerous examples with worked solutions, clear summaries and extensive further reading lists throughout the book. Thorough coverage is given to all classic soil mechanics topics such as boundary value problems and serviceability of structures and to topics which are often missed out of other books or covered more briefly including: the principles of continuum mechanics, Critical State Theory and innovative techniques such as seismic methods. Geotechnical Engineering is suitable for soil mechanics modules on undergraduate civil engineering courses and for use as a core text for specialist graduate geotechnical engineering students. It explores not only the basics but also several advanced aspects of soil behaviour, and outlines principles which underpin more advanced professional work therefore providing a useful reference work for practising engineers. Readers will gain a good grasp of applied mechanics, testing and experimentation, and methods for observing real structures. Renato Lancellotta is Professor of Geotechnical Engineering, Director of the Geotechnical Laboratory and since 1990 has been Head of the Ph.D. Programme on Geotechnical Engineering at the Technical University of Torino, Italy.

Geotechnical Engineering

Second Edition

Renato Lancellotta

First English language edition published 1995 by A. A. Balkema Second English language edition published 2009 by Taylor & Francis 2 Park Square, Milton Park, Abingdon, Oxon, OX14 4RN Simultaneously published in the USA and Canada by Taylor & Francis 270 Madison Ave, New York, NY 10016 Taylor & Francis is an imprint of the Taylor & Francis Group, an informa business This edition published in the Taylor & Francis e-Library, 2008. “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.”

© 2009 Zanichelli editore S.p.A., via Irneroo 34, 40126 Bolonga [7653] All rights reserved. Authorized translation from the Italian Language edition Geotecnica (terza edizione) published by Zanichelli Editore S.p.A. No part of this book may be reprinted or reproduced or utilized 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. The publisher makes no representation, express or implied, with regard to the accuracy of the information contained in this book and cannot accept any legal responsibility or liability for any efforts or omissions that may be made. 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 Lancellotta, Renato. Geotechnical engineering / Renato Lancellotta. – 2nd ed. p. cm. ‘First English language edition published 1995 by A.A. Balkema’–T.p. verso. Includes bibliographical references and index. 1. Engineering geology. 2. Soil mechanics. 3. Rock mechanics. I. Title. TA705.L265 2008 624.1′ 51–dc22 ISBN 0-203-92783-4 Master e-book ISBN

ISBN10: 0-415-42003-2 (hbk) IBSN10: 0-415-42004-0 (pbk) IBSN10: 0-203-97783-4 (ebk) ISBN13: 978-0-415-42003-7 (hbk) ISBN13: 978-0-415-42004-4 (pbk) ISBN13: 978-0-203-92783-0 (ebk)

2007045353

To Donata, Paolo and Giulia

Contents

List of figures and tables Preface 1

Origin, description and classification of soils 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8

2

1

Soil formation 1 Clay particles 5 Soil deposits 9 Phase relations 11 Description and classification of soils 17 Atterberg limits and plasticity chart 22 Summary 26 Further reading 27

Continuum mechanics 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 2.11 2.12 2.13 2.14 2.15 2.16

xi xix

The language of continuum mechanics: indicial notation 29 Tensors 32 Eigenvalues and eigenvectors 37 Vector and tensor fields 39 Kinematics 40 Finite deformation 42 Infinitesimal strains 49 Geometrical interpretation of infinitesimal strains 50 Stress 55 Mohr circle of stress 63 Gauss and Reynolds theorems 65 Conservation of mass 69 Balance of linear momentum 70 Balance of angular momentum 71 Summary 71 Further reading 73

29

viii Contents

3

Basic constitutive models 3.1 3.2 3.3 3.4 3.5 3.6 3.7

4

4.5 4.6 4.7 4.8 4.9 4.10 4.11 4.12 4.13 4.14 4.15 4.16 5

Elasticity 75 Cylindrical coordinates 80 Plasticity 86 Visco-elasticity 93 Internal constraints 97 Summary 98 Further reading 100

The porous medium 4.1 4.2 4.3 4.4

75

101

The principle of effective stress 101 Geostatic stresses 103 Capillarity 107 A mechanistic picture of geological processes: yield stress and overconsolidation ratio 108 Modelling one-dimensional compression: the oedometer test 112 Experimental determination of yield stress 116 Soil compressibility 121 Prediction of one-dimensional compression settlement 124 Secondary compression 125 Further post-depositional phenomena: leaching, exchange of cations, cementation 129 Importance of detailed geological history 130 Importance of sample quality and testing procedures 132 Stress paths 133 On the meaning of the term ‘deviator’ 138 Summary 140 Further reading 140

Stress-strain behaviour of soils 5.1 The ability of soils to carry stresses: soil strength and Coulomb’s failure criterion 142 5.2 Drained and undrained conditions: relative rate of loading 144 5.3 Soil testing: requirements of laboratory apparatuses 145 5.4 Dilatancy, peak and critical state strength 152 5.5 Taylor expression of dissipation of work 155 5.6 Strain localization 161 5.7 State paths: drained and undrained tests on reconstituted samples 163 5.8 State boundary surface 168

142

Contents ix

5.9 Stiff clays: structural features, peak, post-peak and residual strength 172 5.10 Undrained shear strength 182 5.11 Predicting soil behaviour: the original Cam Clay Model 188 5.12 Soil stiffness 193 5.13 Beyond simple models 199 5.14 Summary 200 5.15 Further reading 201 6

Flow in porous media 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 6.10 6.11 6.12 6.13 6.14 6.15 6.16

7

Terminology 202 Darcy’s law 205 Coefficient of hydraulic conductivity 209 Seepage forces 211 Mathematical modelling of flow in porous media 218 Steady state flow 222 Numerical solution of Laplace’s equation 229 Flow through anisotropic and inhomogeneous media 231 Unconfined steady state flow 233 Transient flow: one-dimensional theory of consolidation 237 Experimental determination of the coefficient of consolidation 245 Solution of consolidation PDE 247 Vertical drains 252 Three-dimensional consolidation theory 256 Summary 259 Further reading 260

In situ investigations 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 7.10 7.11 7.12 7.13

202

Exploration programme 261 Methods of investigation 263 Sampling techniques 266 Groundwater conditions 270 In situ testing devices 278 Soil profiling 291 In situ horizontal stress 292 Undrained shear strength 294 Shear strength of coarse-grained soils 303 Stiffness 307 Seismic methods 309 Wave propagation theory 316 Soil porosity from wave propagation 321

261

x Contents

7.14 7.15 7.16 8

The collapse of soil structures 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 8.9 8.10 8.11 8.12 8.13 8.14 8.15 8.16 8.17 8.18 8.19 8.20 8.21 8.22

9

Hydraulic conductivity 323 Summary 333 Further reading 335 336

Theorems of limit analysis 336 Yield criteria 339 Rankine limiting states of stress 345 Coulomb critical wedge analysis 350 Stress discontinuities 353 Earth retaining structures 360 Design of retaining walls 373 Design of diaphragm walls 374 Choice of strength parameters and factor of safety 381 Strutted excavations 384 Earth pressure in presence of seismic actions 386 Bearing capacity of shallow footings 393 Undrained bearing capacity 395 Non-homogeneity and anisotropy 401 Bearing capacity of shallow footings: drained loading 403 Load factor and strength mobilization 409 Bearing capacity: routine analysis 410 Slope stability 414 Limit equilibrium methods 417 Landslides analysis and operational strength 423 Summary 428 Further reading 429

Serviceability limit state

430

9.1 9.2 9.3 9.4 9.5

Description of ground and foundation movements 430 Methods of computing settlements: Introductory notes 433 Prediction using the theory of elasticity 433 Settlement of foundations on clay 448 The use of field tests to predict the settlement of footings on sand 455 9.6 Damage criteria and limiting values of settlement 467 9.7 Summary 470 9.8 Further reading 470 Bibliography Index

472 494

Figures and tables

Figures 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 1.10 1.11 1.12 1.13 1.14 1.15 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 2.11 2.12 2.13 2.14 2.15 3.1

Soil formation Tetrahedral unit Octahedral unit Kaolinite Montmorillonite Illite Diffuse double layer Idealized representation of phases Water content distribution within a continuous sample of Pisa clay Examples of grain size distribution curves Consistency of a clay soil Casagrande apparatus for the determination of the liquid limit Rolling-out test for the determination of plastic limit Plasticity chart Clay minerals on plasticity chart A cartesian coordinate system Change of orthonormal basis Homogeneous extension Pure shear deformation Infinitesimal strains Rigid rotation around the y axis Engineering shear strain The concept of stress Stress components The Cauchy tetrahedron Illustrative example of computing the stress on a plane of unit outward normal n Mohr’s circle Mohr’s circle of stress: origin of planes Analytical relations between stress components and related planes on which they act Illustrative example of computing stress on a specified plane Elastic behaviour

2 4 6 6 7 7 8 12 14 21 22 23 24 25 26 30 36 46 46 51 54 54 56 57 58 62 63 64 65 67 76

xii Figures and tables

3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10 4.11 4.12 4.13 4.14 4.15 4.16 4.17 4.18 4.19 4.20 4.21 4.22 4.23 4.24 4.25 4.26 4.27 5.1 5.2

Cross anisotropy Cylindrical coordinates Uniform axial compression Idealized one-dimensional compression (no lateral displacement) Torsion test Idealized elastic-plastic behaviour Positive and negative hardening Yield surface (a) isotropic hardening; (b) kinematic hardening Yield surface and plastic potential Maxwell model Kelvin model Burgers model Example of rate effect on stress–strain behaviour Geostatic stresses Example of computing geostatic stresses The rise of water in a capillary tube Stress history of a soil element Preconsolidation induced by groundwater level oscillation Oedometer testing apparatus Compression readings versus time Example of one-dimensional compression curves Casagrande’s procedure of determining the yield stress Stress history of Panigaglia clay Soil profile of Pisa subsoil Examples of oedometer tests on Pisa clay Stress history of Pisa clay Soil compressibility Correlation between the compression index and the void ratio Preconsolidation induced by creep Influence of stress history on the coefficient of secondary compression Estimating the preconsolidation induced by creep Effect of weathering on properties of clay Compression curves for clays having different preconsolidation mechanisms The influence of the sequence of events on the effective horizontal stress Influence of disturbance on oedometer test results Influence of sample quality on oedometer test results Influence of secondary compression on the assessment of yield stress The stress-path concept Stress path of a soil element simulating a passive failure of conditions Total (A→B) and effective (A′ → B′ ) stress paths Coulomb failure criterion Failure envelope

79 81 82 84 85 87 89 90 90 91 94 95 96 97 103 106 107 110 113 114 115 116 117 118 119 120 121 122 123 126 128 129 130 131 132 132 134 135 138 139 139 143 144

Figures and tables xiii

5.3 5.4 5.5 5.6 5.7 5.8 5.9 5.10 5.11 5.12 5.13 5.14 5.15 5.16 5.17 5.18 5.19 5.20 5.21 5.22 5.23 5.24 5.25 5.26 5.27 5.28 5.29 5.30 5.31

5.32 5.33 5.34 5.35 5.36 5.37 5.38 5.39 5.40 5.41 5.42 5.43

Triaxial apparatus Typical stress paths performed with triaxial tests Direct shear test Resonant column test Typical behaviour of loosely and densely packed sand Influence of rate of dilation on the peak strength Failure envelope of Hokksund sand Taylor model of dissipation Influence of dilatancy on the peak angle of shear resistance Influence of stress level on the rate of dilation Critical void ratio Definition of state parameter vl Dependence of peak strength on the state parameter vl Choice of shear strength (a) Deformation of a loose sand or soft clay sample; (b) Strain localization in a sample of dense sand or stiff clay Drained test on reconstituted Pisa clay Drained paths and critical state of Pisa clay Critical state and normally consolidation lines Undrained behaviour of Pisa clay Uniqueness of critical state Contours of constant water content for drained and undrained tests The state boundary surface Undrained path of a NC soil sample Undrained paths moving from different initial states Drained path of a NC soil sample Definition of a stiff clay Intact Vallericca clay: peak strength and undrained stress paths Undrained tests on lightly overconsolidated samples: (a) initial condition; (b) failure states Normalization of peak strength: (a) equivalent mean stress; (b) drained paths; (c) normalized representation of the State Boundary Surface Results of triaxial tests on Tody clay Unconsolidated undrained test on Tody clay, with pore pressure measurements Vallericca clay: post-rupture Coulomb strength envelope compared with peak intact and intrinsic Mohr-Coulomb failure lines Direct shear test on Santa Barbara Clay Shear strength of intact clay and along joints Decrease of residual strength with increasing clay fraction Failure criterion in terms of total stress Undrained strength of Panigaglia clay Stress history of an overconsolidated clay Increase in undrained strength with OCR Stress states of soil elements along a failure surface Dependence of undrained strength on loading path

146 148 149 151 152 153 154 155 157 158 159 160 160 161 162 164 165 166 167 168 169 170 171 171 172 173 174 175

177 178 180 181 181 182 183 183 185 185 187 187 188

xiv Figures and tables

5.44 5.45 5.46 5.47 5.48 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 6.10 6.11 6.12 6.13 6.14 6.15 6.16 6.17 6.18 6.19 6.20 6.21 6.22 6.23 6.24 6.25 6.26 6.27 6.28 6.29 6.30 6.31 6.32 6.33

Elastic domain Elastic and plastic volume strain Decay of shear modulus with strain level Shear wave propagation through a laboratory soil sample Drained test on lightly overconsolidated Pisa clay Equipotential and flow lines Elevation, pressure and velocity head Darcy’s law Illustrative example of determining the pressure head (downward flow) Permeability tests Piping and heave Computing the effective stress for the case of hydrostatic condition, upward and downward flow Computing the hydraulic gradient through a linearized flow pattern Checking against failure by uplift of the bottom of excavation Seepage under a diaphragm wall Solution of the case of seepage under a diaphragm wall Seepage under an impervious structure Numerical solution of Laplace’s equation The condition of continuity Boundary between two isotropic zones of different hydraulic conductivity Unconfined flow Parabolic free surface Confocal parabolas Flow through an earth dam One-dimensional consolidation problem Solution of one-dimensional consolidation Average degree of consolidation for different initial isochrones Illustrative example of consolidation induced by surface load Illustrative example of subsidence induced by underdrainage Determining the consolidation coefficient of consolidation by means of square root method Influence of stress history and soil disturbance on Cv The consolidation coefficient as backfigured from field measurements and lab tests Preloading embankment on vertical drains Consolidation process in presence of vertical drains Rate of consolidation of a circular footing for drainage boundaries PTPB Rate of consolidation of a circular footing for drainage boundaries PTIB Rate of consolidation of strip footing for drainage boundaries PTPB Rate of consolidation of strip footing for drainage boundaries PTIB

189 191 194 197 198 203 205 207 209 210 214 216 217 218 224 226 228 230 230 233 234 235 236 236 239 241 242 243 244 246 248 248 253 254 257 257 258 258

Figures and tables xv

7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 7.10 7.11 7.12 7.13 7.14 7.15 7.16 7.17 7.18 7.19 7.20 7.21 7.22 7.23 7.24 7.25 7.26 7.27 7.28 7.29 7.30 7.31 7.32 7.33 7.34 7.35 7.36 7.37 7.38 7.39 7.40 7.41 7.42 7.43 7.44 7.45

Planning for subsoil exploration Characteristics of samplers Stationary piston sampler Continuous sampler Double tube core barrels Groundwater conditions Open standpipe piezometer Sealed open standpipe piezometer Casagrande piezometer Bishop-type piezometer Time-lag analysis Intake sections SPT split-spoon sampler Mechanical cone penetrometer Typical design of electric friction cone penetrometer Schematic sections of piezocone tips Marchetti dilatometer Vane test Menard’s pressuremeter Self-boring pressuremeters: (a) Pafsor; (b) Camkometer Design of a plate load test at depth Cross-hole and down-hole tests Seismic dilatometer SASW test CPTU test at Ravenna site Examples of expansion curves from pressuremeter tests Correlation between Ko and horizontal stress index Interpretation of field vane test Vane correction factor Interpretation of a pressuremeter test Example of expansion curve from a pressuremeter test Interpreting a pressuremeter test according to Windle and Wroth (1977) procedure The calibration chamber Relative density from STP Correlations suggested by Gibbs and Holtz (1957) and Bazaraa (1967) Relative density from cone resistance Interpretation of the dilatometer test Example of a pressuremeter test in Po river sand Wave propagation in a cross-anisotropic medium Down-hole test: direct arrival approach Soil depth tested by different wavelengths Rayleigh wave velocity in uniform homogeneous half-space Rayleigh wave velocity in a layer overlying a half-space Example of dispersion curve Difference between group and phase velocity

263 267 268 269 270 271 272 273 274 274 276 277 280 281 282 283 284 285 286 287 288 289 290 290 291 292 294 295 296 300 302 302 304 305 306 307 308 310 311 312 313 314 314 315 315

xvi Figures and tables

7.46 7.47 7.48 7.49 7.50 7.51 7.52 7.53 7.54 7.55 7.56 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 8.9 8.10 8.11 8.12 8.13 8.14 8.15 8.16 8.17 8.18 8.19 8.20 8.21 8.22 8.23 8.24 8.25 8.26 8.27 8.28 8.29 8.30

Profile of shear wave velocity in Pisa clay, a...