Contents

Preface x

Notation index xii

1 Classification and Identification Properties of Soil 1

1.1 Agricultural and engineering soil 1

1.2 Engineering definitions 2

1.3 Clays 4

1.4 Soil classification 6

1.5 Common types of soil 15

1.6 Soil classification and description 15

1.7 Soil properties 22

1.8 Soil physical relations 30 Exercises 31

2 Soil Water, Permeability and Flow 34

2.1 Subsurface water 34

2.2 Flow of water through soils 36

2.3 Darcy's law of saturated flow 37

2.4 Coefficient of permeability (k) 37

2.5 Determination of k in the laboratory 38

2.6 Determination of k in the field 41

2.7 Approximation of k 44

2.8 General differential equation of flow 44

2.9 Potential and stream functions 46

2.10 Flow nets 47

2.11 Hydraulic gradient 47

2.12 Calculation of seepage quantities from a flow net 49

2.13 Drawing a flow net 50

2.14 Critical hydraulic gradient 52

2.15 Seepage forces 53

2.16 Alleviation of piping 53

2.17 Design of filters 54

2.18 Total and effective stress 58

2.19 Capillarity 58

2.20 Earth dams 62

2.21 The problem of stratification 68

2.22 Calculation of seepage quantities in an anisotropic soil 69

2.23 Other solutions to seepage problems 72

2.24 Permeability of sedimentary deposits 74

2.25 Seepage through soils of different permeability 76

2.26 Refraction of flow lines at interfaces 77 Exercises 79

3 Shear Strength of Soils 82

3.1 Friction 82

3.2 Complex stress 83

3.3 The Mohr circle diagram 84

3.4 Cohesion 88

3.5 Coulomb's law of soil shear strength 88

3.6 Modified Coulomb's law 90

3.7 The Mohr-Coulomb yield theory 90

3.8 Determination of the shear strength parameters 91

3.9 Determination of the total stress parameters <pu and cu 99

3.10 Determination of the effective stress parameters $ and c' 101

3.11 The pore pressure coefficients A and B 105

3.12 The triaxial extension test 109

3.13 Behaviour of soils under shear 113

3.14 Variation of the pore pressure coefficient A 117

3.15 Operative strengths of soils 118

3.16 Space diagonal and octahedral plane 120

3.17 Sensitivity of clays 125

3.18 Activity of a clay 126

3.19 Residual strength of soil 127 Exercises 130

4 Elements of Stress Analysis 134

4.1 Stress-strain relationships 134

4.2 The state of stress at a point within a soil mass 135

4.3 Stresses induced by the self weight of the soil 136

4.4 Stresses induced by applied loads 137

4.5 Influence charts for vertical stress increments 142

4.6 Bulbs of pressure 144

4.7 Shear stresses 146

4.8 Contact pressure 148 Exercises 149

5 Stability of Slopes 151

5.1 Granular materials 151

5.2 Soils with two strength components 154

5.3 Methods of investigating slope stability 154

5.4 Total stress analysis 155

5.5 Effective stress analysis 167

5.6 Planar failure surfaces 181 Exercises 185

6 Lateral Earth Pressure 196

6.1 Introduction 196

6.2 Active and passive earth pressure 196

6.3 Active pressure in cohesionless soils 198

6.4 Surcharges 205

6.5 The effect of cohesion on active pressure 211

6.6 Choice of method for prediction of active pressure 219

6.7 Design parameters for different soil types 221

6.8 The choice of backfill material 223

6.9 Earth pressure at rest 229

6.10 Influence of wall yield on design 229

6.11 Strutted excavations 231

6.12 Passive pressure in cohesionless soils 232

6.13 The effect of cohesion on passive pressure 235

6.14 Operative values for <f> and c for passive pressure 237 Exercises 238

7 Earth Retaining Structures 240

7.1 Main types of earth retaining structures 240

7.2 Gravity wall 240

7.3 Embedded wall 243

7.4 Design of earth retaining structures 245

7.5 Design of gravity walls 247

7.6 Design of sheet pile walls 252

7.7 Reinforced soil 264

7.8 Soil nailing 266

7.9 Anchored earth 268

8 Bearing Capacity of Soils 269

8.1 Bearing capacity terms 269

8.2 Types of foundations 269

8.3 Analytical methods for the determination of the ultimate bearing pressure of a foundation 270

8.4 Determination of the safe bearing capacity 278

8.5 The effect of ground water on bearing capacity 278

8.6 Developments in bearing capacity equations 279

8.7 Effect of eccentric and inclined loading on foundations 282

8.8 Non-homogeneous soil conditions 285

8.9 In situ testing for ultimate bearing capacity 288

8.10 Pile foundations 295 Exercises 310

9 Foundation Settlement and Soil Compression 312

9.1 Settlement of a foundation 312

9.2 Immediate settlement 313

9.3 Consolidation settlement 324

9.4 Two-dimensional stress paths 342

9.5 Foundation design criteria 348 Exercises 349

10 Rate of Foundation Settlement 352

10.1 Analogy of consolidation settlement 352

10.2 Distribution of the initial excess pore pressure, u; 353

10.3 Terzaghi's theory of consolidation 353

10.4 Average degree of consolidation 356

10.5 Drainage path length 357

10.6 Determination of the coefficient of consolidation, cv, from the consolidation test 358

10.7 Determination of the permeability coefficient from the consolidation test 360

10.8 Determination of the consolidation coefficient from the triaxial test 360

10.9 The model law of consolidation 362

10.10 Consolidation during construction 364

10.11 Consolidation by drainage in two and three dimensions 367

10.12 Numerical determination of consolidation rates 367

10.13 Construction pore pressures in an earth dam 372

10.14 Numerical solutions for two- and three-dimensional consolidation 374

10.15 Sand drains 377 Exercises 382

11 Compaction and Soil Mechanics Aspects of Highway Design 384

11.1 Laboratory compaction of soils 384

11.2 Main types of compaction plant 392

11.3 Moisture content value for in situ compaction 394

11.4 Specification of the field compacted density 395

11.5 In situ tests carried out during earthwork construction 396

11.6 Highway design 399 Exercises 415

12 Unsaturated Soils 417

12.1 Partially saturated, or unsaturated, soils 417

12.2 Measurement of soil suction 420

12.3 Practical applications 423

12.4 Equilibrium moisture content 425

12.5 Soil structure changes with water content 429

12.6 Effective stress in unsaturated soils 432

12.7 More recent research work 435

12.8 Testing techniques for unsaturated soils 437

13 Critical State Theory 441

13.1 Critical state theory 441

13.2 Symbols 441

13.3 Critical state 442

13.4 Isotropic consolidation 442

13.5 Stress paths in three-dimensional stress space 445

13.6 The critical state line 447

13.7 Representation of triaxial tests in p'-q-v space 449

13.8 The Roscoe surface 452

13.9 The overall state boundary 455

13.10 Equation of the Hvorslev surface 456

13.11 Residual and critical strength states 458

14 Site Investigation and Ground Improvement 459

14.1 Desk study 459

14.2 Site reconnaissance 460

14.3 Ground investigation 461

14.4 Site investigation reports 469

14.5 Ground improvement 471

14.6 Environmental geotechnics 476

References 477

Index 487

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