SOIL MECHANICS: Principles and Practice THIRD EDITION Graham Barnes palgrave macmiiian
'running Contents Preface xii Fine soil 19 List of symbols xiv Mass structure 21 Note on units xix Degree of weathering 22 List of case studies XX Geological origin Soil classification Particle 1 Soil formation and density 23 nature 1 Particle shape 24 Objectives 1 Particle size distribution 24 Soil formation 1 Grading characteristics 27 Manmade soils 1 Density 28 Contaminated and polluted soils 2 Density Index 29 Naturally occurring soils 2 Moisture content or water content 30 In situ soils weathered rocks 2 Atterberg limits 31 In situ soils peat 3 Activity Index 35 Waterborne soils 3 Shrinkage limit 36 Glacial deposits 4 Soil model 36 Windblown soils 6 Summary 39 Soil particles 6 Worked examples 39 Nature of particles 6 Exercises 46 Clay minerals 8 Soil structure 10 Cohesive soils 10 3 Permeability and seepage 47 Granular soils 13 Objectives 47 Summary 13 Permeability Introduction 47 47 2 Soil description and classification 14 Groundwater 47 Flow problems 48 Objectives 14 Flow into excavations 48 Soil description 14 Flow around cofferdams 48 Soil categories 14 Dewatering 48 Made ground 14 Flow through earth structures 49 Organic soils 15 Stability problems sand' 49 Volcanic soil 15 Boiling or heaving in cofferdams 49 Particle size fractions fundamental basis 16 Piping 50 Very coarse soil 16 Heaving beneath a clay layer 50 Coarse soil 17 Uplift pressures 50 Fines 18 Soil voids 50 Composite soils 18 Pressure and head 51 22 22
packer piezometers triaxial point theory Darcy's law 51 Normally consolidated clay 98 Effect of temperature 52 Overconsolidated clay 101 Empirical correlations for k 52 Desiccated crust 103 Layered soils 54 Present state of stress in the ground 103 Laboratory test constant head permeameter 55 Mohr's circle of stress 104 Laboratory test falling head permeameter 56 In situ horizontal and vertical stresses 104 Laboratory test hydraulic cell vertical Changes in stress due to engineering permeability 57 structures 108 Laboratory test hydraulic cell horizontal Pore pressure parameters 110 permeability 58 Pore pressure parameters A and B 111 Laboratory test ~ cell vertical Capillary rise above the water table 112 permeability 58 Effective stresses above the water table 114 Borehole tests open borehole 58 Desiccation of clay soils 115 Borehole tests tests 61 Suctions 116 Borehole tests 62 Frost action in soils 118 Pumping tests 63 Frost heave test 120 Seepage 63 Permafrost 121 Seepage theory 63 Ground freezing 121 Flow nets 66 Summary 122 Flow net construction 67 Case study 123 Seepage quantities 69 Worked examples 125 Total head, elevation head and pressure head 70 Exercises 130 Pore pressure and uplift pressure 71 Failure by uplift (buoyancy) Seepage force 71 72 Quick condition, boiling and internal erosion 72 5 Contact pressure and stress distribution 132 Critical hydraulic gradient 73 Objectives 132 Failure by internal erosion 73 Contact pressure 132 Failure by heave sheet piling 73 Contact pressure uniform loading 132 Failure by piping 74 Contact pressure loading 133 Seepage through earth dams 74 Stress distribution 134 Seepage through flood banks, levees 74 Stresses beneath point load and line Soil filters 76 load 134 Summary 78 Assumptions 134 Case studies 79 Stresses beneath uniformly loaded areas 136 Worked examples 83 Bulbs of pressure 137 Exercises 94 Stresses beneath a flexible rectangle Principle of superposition I Effective stress and pore pressure 97 Stresses beneath flexible area of any shape Objectives 97 rectangle Stresses beneath a flexible 137 137 137 finite soil thickness 137 Total stress 97 Stresses beneath a rigid rectangle 139 Pore pressure below the water table 97 Embankment loading 141 Effective stress 98 Summary 143 Effective stress in the ground 98 Worked examples 144 Stress history 98 Exercises 149
log 6 Compressibility and consolidation 150 Objectives 150 Introduction 150 Compressibility 150 Void ratio/effective stress plot 150 Reloading curves 151 Preconsolidation pressure cxp' and overconsolidated ratio OCR 152 Casagrande method for c ' 152 Effect of sampling disturbance 153 In situ curve for normally consolidated clay 153 In situ curve for overconsolidated clay 153 Effect of load increments 154 Effect of duration of load 154 Effect of secondary compressions 155 Isotropic compression 156 Anisotropic compression 156 Consolidation 157 Terzaghi theory of onedimensional consolidation 157 Solution of the consolidation equation 159 Isochrones 159 Average degree of consolidation 160 Oedometer test 162 Coefficient of consolidation, cv root time method 164 Coefficient of consolidation, cv time method 166 In situ cy values 167 Rowe consolidation cell 167 Two and threedimensional consolidation 169 Correction for construction period 170 Precompression by surcharging 171 Radial consolidation for vertical drains 172 Summary 175 Case studies 176 Worked examples 180 Exercises 188 7 Shear strength 190 Objectives 190 Introduction 190 Stresses and strains in soils 191 Representation of stresses 191 Pole 191 Principal stresses 191 Axial symmetry 192 Plane strain 192 0 condition 192 Normal and shear strains 192 Mohr circle of strain 194 Volumetric strains 194 Shear strength 194 Effect of strain 194 Idealised stressstrain relationships 197 Yield and plasticity 197 Flow rule and normality 198 Failure criterion 199 Failure of soil in the ground 199 Stress paths 201 Effects of drainage 202 Test procedures 205 Shear strength of sand 206 Stressstrain behaviour 206 Shear box test 207 Effect of packing and particle nature 208 Constant volume condition 210 Effect of density 210 Shear strength of clay 211 Effect of sampling 211 Undrained cohesion, cu 211 Strength index tests 211 Strength tests 212 Laboratory vane test 212 Fall cone test 212 Unconfined compression test 212 Field vane test 213 Triaxialtest 214 Triaxial unconsolidated undrained (UU) test 216 Multistage (UU) test 217 Effect of clay content and mineralogy 218 Partially saturated clays 218 Fissured clays 218 Variation with depth 219 Frictional characteristics 221 Test procedures 221 Triaxial consolidated undrained (CU) test 222 Triaxial consolidated drained (CD) test 224 Critical state theory 224 Parameters 225 State boundary surface 225 Isotropic normal consolidation line (ICL) 225 KQ normal consolidation line (KQ CL) 227 Critical state line (CSL) 227
stability Roscoe surface 228 Foundation design 263 Tension cutoff 229 Design requirements 263 Hvorslev surface 229 Traditional approach compared with the The elastic wall 230 Eurocodes 264 Real soils 231 Bearing resistance 264 Residual strength 231 Modes of failure 264 Summary 233 Bearing capacity and bearing resistance 266 Case study 234 Shape factors 267 Worked examples 236 Depth factors 267 Exercises 241 Base inclination factors Bearing resistance overturning 267 268 8 Geotechnical Eurocodes 243 Eccentric loading 268 Inclined loading 270 Objectives 243 Different soil strength cases 270 Relevant Eurocodes 243 Effect of water table 271 Personnel 243 Net ultimate bearing capacity 271 Geotechnical Design Report 243 Effect of compressibility of soil 271 Geotechnical Risk 244 Sliding 271 Durability 245 Allowable bearing pressure of sand 272 Geometrical data 245 Introduction 272 Limit states 246 Settlement limit 272 Verification of limit states 247 Allowable bearing pressure 272 Design by prescriptive measures 247 Corrected SPT N values 273 Design by experimental models and Summary 275 load tests 247 Case studies 276 Observational method 247 Worked examples 279 Design by calculation 248 Exercises 285 Models and model factors 248 Actions 248 10 Shallow foundations Design situations and values of actions 248 settlements 287 Characteristic and representative values of actions 249 Objectives 287 Design values of actions 249 Introduction 287 Effects of actions E& 249 Are settlement calculations required? 288 Design resistances 249 Immediate settlement 289 Design approach and partial factors 249 General method 289 Characteristic values of geotechnical Principle of superposition 290 parameters 251 Principle of layering 290 Summary 254 Rigidity correction Depth correction 290 291 9 Shallow foundations 255 Average settlement 291 Modulus increasing with depth 291 Objectives 255 Effect of local yielding 292 Shallow foundations 255 Estimation of undrained modulus Ea 294 Definition 255 Consolidation settlement 295 Spread foundations 255 General 295 Types of foundation 256 Compression index Cc method 296 Depth of foundations 259 Oedometer modulus oed or mv method 297
undrained passive gravity embedded Total settlement 298 SkemptonBjerrum method 298 Elastic drained method 299 Estimation of drained modulus E 299 Proportion of immediate to total settlement 299 Secondary compression 302 Introduction 302 General method 302 Estimation of Ca or ea values 303 Sands 304 Methods of estimating settlements 304 Schmertrnann's method 304 Burland and Burbridge's method 306 Permissible settlements 307 Definitions of ground and foundation movement 307 Criteria for movements 309 Routine settlement limits 309 Summary 311 Case studies 312 Worked examples 317 Exercises 324 11 Pile foundations 326 Objectives 326 Pile foundations 326 Introduction 326 Types of pile 326 Loading conditions 326 Uncertainty of design calculation methods 327 Limit states 328 Pile load tests 328 Ultimate compressive resistance from static load tests 329 Ultimate compressive resistance from ground test results 330 Ultimate compressive resistance from other methods 330 Weight of pile 331 Bored piles in clay 332 End bearing resistance qh 332 Adhesion ca 332 Driven piles in clay 334 End bearing resistance qh 334 Adhesion installation effects ca 334 Adhesion values ca 334 Effective stress approach for adhesion 336 Driven piles in sand 336 Effects of installation 336 End bearing resistance qb 337 Critical depth 337 Skin friction/s 339 Bored piles in sand 340 Mobilisation of base and shaft loads 340 Downdrag (negative skin friction) 341 Causes of downdrag 341 Determination of downdrag 342 Pile groups 342 Stiffness of pile cap and structure 342 Pile spacing 342 Stressed zone 343 Load variation 343 Efficiency 343 Ultimate capacity 344 Settlement ratio 345 Settlement of pile groups 347 Summary 348 Case studies 349 Worked examples 352 Exercises 358 12 Lateral earth pressures and retaining structures 360 Objectives 360 Lateral earth pressures 360 Introduction 360 Effect of horizontal movement 360 Effect of wall flexibility and propping 364 Effect of wall friction 364 Coulomb theory active force 365 Coulomb theory force 366 Limitations of the Coulomb theory 366 Earth pressure coefficients 367 Effect of cohesion intercept c' 369 Minimum equivalent fluid pressure 369 Effect of water table walls 370 Effect of water table walls 371 Undrained conditions 372 Earth pressures condition 372 Tension cracks 373 Uniform surcharge 373 Line loads and point loads 374 Earth pressures due to compaction 374
deep general tieback construction design general design single multiplane r general method limit Retaining structures 376 Introduction 376 Basement walls 376 Bridge abutments 379 Gabions and cribwork 379 Design of gravity walls 379 Serviceability limit states 379 Ultimate limit states 379 Loss of overall stability 380 Overturning or rotational failure 380 Bearing pressure under the toe 380 Bearing capacity 381 Sliding 382 Failure of structural elements 382 Design of embedded walls 382 Cantilever embedded walls Cantilever embedded walls 383 383 Single anchor or propped embedded walls general 384 Single anchor or propped embedded walls design 384 Design methods 384 Gross pressure method 384 Net available passive resistance method 385 Factor on strength method 385 BS8002 method 386 Anchorages for embedded walls 386 Strutted excavations and cofferdams 387 Introduction 387 Strut loads 387 Base stability of excavations 388 Base stability shallow excavations 388 Base stability excavations 389 Reinforced soil 389 Reinforced soil walls 389 Effects of reinforcement 390 Reinforced soil walls 390 External stability 391 Internal stability 392 Tensile rupture 393 Pullout resistance or adherence 393 Internal stability wedge method 394 Coherent gravity method 395 Summary 397 Case studies 398 Worked examples 402 Exercises 415 13 Slope stability 417 Objectives 417 Natural and artificial slopes 417 Introduction 417 Types of mass movement 417 Natural slopes 417 Artificial slopes or earthworks 420 Shortterm and longterm conditions 421 Methods of analysis 425 Plane translational slide Plane translational slide Eurocode 425 approach 425 Plane translational slide special cases 426 Stability of vertical cuts 428 Circular arc analysis general 429 Circular arc analysis undrained condition or 0U = 0 analysis 429 Tension crack 430 Undrained analysis stability charts Taylor's method 431 Effective stress analysis 432 Effective stress analysis of slices 432 Bishop simplified method 433 Bishop simplified method state approach 434 Pore pressure ratio ru 435 Stability coefficients Stability coefficients method 435 water table method 438 Submerged slopes 439 Rapid drawdown 439 Noncircular slip surfaces 440 Wedge method Wedge method plane 441 441 Factors affecting stability and slope design 443 Summary 444 Case studies 445 Worked examples 449 Exercises 459 14 Earthworks and soil compaction 462 Objectives 462 Earthworks 462 Introduction 462 Construction plant 462
Purpose and types of materials 463 Material requirements 466 Suitability of fill material 466 Suitability of granular soils 467 Suitability of cohesive soils 468 Moisture condition test 469 Efficiency of earthmoving 471 Material problems 471 Softening 471 Bulking 472 Soil compaction 474 Factors affecting compaction 474 Field compaction 476 Compaction plant 476 Specification of compaction 478 Control of compaction in the field 480 Laboratory compaction 482 Light compaction test 482 Heavy compaction 483 Vibrating hammer 483 Air voids lines 484 Correction for oversize particles 484 California Bearing Ratio (CBR) test 484 Addition of lime 485 Cement stabilisation 486 Summary 487 Case study 488 Worked examples 490 Exercises 497 15 Site investigation 499 Objectives 499 Site investigation 499 Introduction 499 Relationship with geotechnical design 500 Stages of investigation 501 Desk study 501 Site inspection 501 Ground investigation 501 Extent of the ground investigation 501 Depth of exploration 502 Choice of method of investigation 503 Methods of ground investigation 504 Undisturbed sampling sampling quality 508 Types of samples 509 Methods of in situ testing 512 Dilatometer tests 515 Groundwater observations 516 Investigation of contaminated land 519 Ground investigation report 520 Presentation of geotechnical information 520 Factual report 520 Geotechnical evaluation 522 Summary 525 Answers to Exercises 526 Glossary 528 References 530 Index 540