Theory and Practice of Pile Foundations
Theory and Practice of Pile Foundations
Contents
List of FiguresPreface
Author
List of Symbols
1 Strength and stiffness from in situ tests
1.1 Standard penetration tests (SPT)1.1.1 Modification of raw SPT values
1.1.1.1 Method A
1.1.1.2 Method B
1.1.2 Relative density 3
1.1.3 Undrained soil strength vs. SPT N
1.1.4 Friction angle
1.1.5 Parameters affecting strength
1.2 Cone penetration tests
1.2.1 Undrained shear strength
1.2.2 SPT blow counts using q c
1.3 Soil stiffness
1.4 Stiffness and strength of rock
1.4.1 Strength of rock
1.4.2 Shear modulus of rock
2 Capacity of vertically loaded piles
2.1 Introduction2.2 Capacity of single piles
2.2.1 Total stress approach: Piles in clay
2.2.1.1 α Method (τ s = αs u and q b )
2.2.1.2 λ Method: Offshore piles 22
2.2.2 Effective stress approach 23
2.2.2.1 β Method for clay (τ s = βσ′ vs ) 23
2.2.2.2 β Method for piles in sand (τ s = βσ′ vs ) 23
2.2.2.3 Base resistance q b (= N q σ′ vb ) 27
2.2.3 Empirical methods 29
2.2.4 Comments 30
2.2.5 Capacity from loading tests 32
2.3 Capacity of single piles in rock 34
2.4 Negative skin friction 35
2.5 Capacity of pile groups 38
2.5.1 Piles in clay 39
2.5.2 Spacing 39
2.5.3 Group interaction (free-standing groups) 40
2.5.4 Group capacity and block failure 41
2.5.4.1 Free-standing groups 41
2.5.4.2 Capped pile groups versus free-standing pile groups 42
2.5.5 Comments on group capacity 44
2.5.6 Weak underlying layer 44
3 Mechanism and models for pile–soil interaction
3.1 Concentric cylinder model (CCM) 473.1.1 Shaft and base models 47
3.1.2 Calibration against numerical solutions 49
3.1.2.1 Base load transfer factor 51
3.1.2.2 Shaft load transfer factor 52
3.1.2.3 Accuracy of load transfer approach 55
3.2 Nonlinear concentric cylinder model 59
3.2.1 Nonlinear load transfer model 59
3.2.2 Nonlinear load transfer analysis 64
3.2.2.1 Shaft stress-strain nonlinearity effect 64
3.2.2.2 Base stress-strain nonlinearity effect 65
3.3 Time-dependent CCM 65
3.3.1 Nonlinear visco-elastic stress-strain model 67
3.3.2 Shaft displacement estimation 69
3.3.2.1 Visco-elastic shaft model 69
3.3.2.2 Nonlinear creep displacement 72
3.3.2.3 Shaft model versus model loading tests 74
3.3.3 Base pile–soil interaction model 77
3.3.4 GASPILE for vertically loaded piles 78
3.3.5 Visco-elastic model for reconsolidation 78
3.4 Torque-rotation transfer model 78
3.4.1 Nonhomogeneous soil profile 79
3.4.2 Nonlinear stress-strain response 79
3.4.3 Shaft torque-rotation response 80
3.5 Coupled elastic model for lateral piles 81
3.5.1 Nonaxisymmetric displacement and stress field 82
3.5.2 Short and long piles and load transfer factor 83
3.5.3 Subgrade modulus 87
3.5.4 Modulus k for rigid piles in sand 90
3.6 Elastic-plastic model for lateral piles 93
3.6.1 Features of laterally loaded rigid piles 94
3.6.1.1 Critical states 94
3.6.1.2 Loading capacity 96
3.6.2 Generic net limiting force profiles (LFP) (plastic state) 98
4 Vertically loaded single piles
4.1 Introduction 1054.2 Load transfer models 106
4.2.1 Expressions of nonhomogeneity 106
4.2.2 Load transfer models 106
4.3 Overall pile–soil interaction 108
4.3.1 Elastic solution 109
4.3.2 Verification of the elastic theory 110
4.3.3 Elastic-plastic solution 113
4.4 Paramatric study 119
4.4.1 Pile-head stiffness and settlement ratio (Guo and Randolph 1997a) 119
4.4.2 Comparison with existing solutions (Guo and Randolph 1998) 119
4.4.3 Effect of soil profile below pile base (Guo and Randolph 1998) 122
4.5 Load settlement 122
4.5.1 Homogeneous case (Guo and Randolph 1997a) 125
4.5.2 Nonhomogeneous case (Guo and Randolph 1997a) 126
4.6 Settlement influence factor 127
4.7 Summary 131
4.8 Capacity for strain-softening soil 132
4.8.1 Elastic solution 132
4.8.2 Plastic solution 134
4.8.3 Load and settlement response 135
4.9 Capacity and cyclic amplitude 142
5 Time-dependent response of vertically loaded piles
5.1 Visco-elastic load transfer behavior 1475.1.1 Model and solutions 148
5.1.1.1 Time-dependent load transfer model 148
5.1.1.2 Closed-form solutions 149
5.1.1.3 Validation 151
5.1.2 Effect of loading rate on pile response 152
5.1.3 Applications 152
5.1.4 Summary 156
5.2 Visco-elastic consolidation 158
5.2.1 Governing equation for reconsolidations 159
5.2.1.1 Visco-elastic stress-strain model 159
5.2.1.2 Volumetric stress-strain relation of soil skeleton 160
5.2.1.3 Flow of pore water and continuity of volume strain rate 162
5.2.1.4 Comments and diffusion equation 163
5.2.1.5 Boundary conditions 163
5.2.2 General solution to the governing equation 163
5.2.3 Consolidation for logarithmic variation of u o 165
5.2.4 Shaft capacity 168
5.2.5 Visco-elastic behavior 169
5.2.6 Case study 171
5.2.6.1 Comments on the current predictions 175
5.2.7 Summary 175
6 Settlement of pile groups
6.1 Introduction 1776.2 Empirical methods 178
6.3 Shallow footing analogy 178
6.4 Numerical methods 180
6.4.1 Boundary element (integral) approach 180
6.4.2 Infinite layer approach 181
6.4.3 Nonlinear elastic analysis 182Contents ix
6.4.4 Influence of nonhomogeneity 182
6.4.5 Analysis based on interaction factors and superposition principle 183
6.5 Boundary element approach: GASGROUP 184
6.5.1 Response of a pile in a group 184
6.5.1.1 Load transfer for a pile 184
6.5.1.2 Pile-head stiffness 185
6.5.1.3 Interaction factor 186
6.5.1.4 Pile group analysis 187
6.5.2 Methods of analysis 187
6.5.3 Case studies 192
6.6 Comments and conclusions 199
7 Elastic solutions for laterally loaded piles
7.1 Introduction 2017.2 Overall pile response 202
7.2.1 Nonaxisymmetric displacement and stress field 202
7.2.2 Solutions for laterally loaded piles underpinned by k and N p 205
7.2.3 Pile response under various boundary conditions 208
7.2.4 Load transfer factor γ b 209
7.2.5 Modulus of subgrade reaction and fictitious tension 211
7.3 Validation 212
7.4 Parametric study 212
7.4.1 Critical pile length 212
7.4.2 Short and long piles 213
7.4.3 Maximum bending moment and the critical depth 213
7.4.3.1 Free-head piles 213
7.4.3.2 Fixed-head piles 216
7.4.4 Effect of various head and base conditions 216
7.4.5 Moment-induced pile response 218
7.4.6 Rotation of pile-head 218
7.5 Subgrade modulus and design charts 218
7.6 Pile group response 220
7.6.1 Interaction factor 220
7.7 Conclusion 227x Contents
8 Laterally loaded rigid piles
8.1 Introduction 2298.2 Elastic plastic solutions 230
8.2.1 Features of laterally loaded rigid piles 230
8.2.2 Solutions for pre-tip yield state (Gibson p u , either k) 232
8.2.3 Solutions for pre-tip yield state (constant p u and constant k) 237
8.2.4 Solutions for post-tip yield state
8.2.5 Solutions for post-tip yield state (constant p u and constant k) 241
8.2.8 Yield at rotation point (YRP, either p u ) 245
8.2.9 Maximum bending moment
8.2.9.2 Yield at rotation point (Gibson p u ) 248
8.2.10 Maximum bending moment and
8.2.10.2 Yield at rotation point (constant p u ) 249
8.2.11 Calculation of nonlinear response 250
8.3 Capacity and lateral-moment loading loci 253
8.3.1 Lateral load-moment loci at tip-yield and YRP state 253
8.3.2 Ultimate lateral load H o against existing solutions 255
8.3.3 Lateral–moment loading locus 257Contents xi
8.3.3.1 Impact of p u profile (YRP
8.3.3.2 Elastic, tip-yield, and YRP loci for constant p u 261
8.3.3.3 Impact of size and base (pile-tip) resistance 264
8.4 Comparison with existing solutions 266
8.5 Illustrative examples 268
8.6 Summary 275
9 Laterally loaded free-head piles
9.1 Introduction 2779.2 Solutions for pile–soil system 279
9.2.1 Elastic-plastic solutions 280
9.2.1.1 Highlights for elastic-plastic response profiles 280
9.2.1.2 Critical pile response 284
9.2.2 Some extreme cases 286
9.2.3 Numerical calculation and
back-estimation of LFP 292
9.3 Slip depth versus nonlinear response 296
9.4 Calculations for typical piles 296
9.4.1 Input parameters and use of GASLFP 296
9.5 Comments on use of current solutions 308
9.5.1 32 Piles in clay 308
9.5.2 20 Piles in sand 313
9.5.3 Justification of assumptions 322
9.6 Response of piles under cyclic loading 325
9.6.1 Comparison of p-y(w) curves 325
9.6.2 Difference in predicted pile response 327
9.6.3 Static and cyclic response of piles in calcareous sand 328
9.7 Response of free-head groups 334
9.7.1 Prediction of response of pile groups (GASLGROUP) 335
9.8 Summary 339
10 Structural nonlinearity and response of rock-socket piles
10.1 Introduction 341xii Contents10.2 Solutions for laterally loaded shafts 343
10.2.1 Effect of loading eccentricity on shaft response 343
10.3 Nonlinear structural behavior of shafts 346
10.3.1 Cracking moment M cr and effective flexural rigidity E c I e 346
10.3.2 M ult and I cr for rectangular and circular cross-sections 347
10.3.3 Procedure for analyzing nonlinear shafts 350
10.3.4 Modeling structure nonlinearity 350
10.4 Nonlinear piles in sand/clay 352
10.4.1 Taiwan tests: Cases SN1 and SN2 352
10.4.2 Hong Kong tests: Cases SN3 and SN4 356
10.4.3 Japan tests: CN1 and CN2 359
10.5 Rock-socketed shafts 361
10.5.1 Comments on nonlinear piles and rock-socketed shafts 371
10.6 Conclusion 372
11 Laterally loaded pile groups
11.1 Introduction 37511.2 Overall solutions for a single pile 376
11.3 Nonlinear response of single piles and pile groups 379
11.3.1 Single piles 379
11.3.2 Group piles 381
11.4 Examples 386
11.5 Conclusions 401
12 Design of passive piles
12.1 Introduction 40512.1.1 Flexible piles 406
12.1.2 Rigid piles 407
12.1.3 Modes of interaction 408
12.2 Mechanism for passive pile–soil interaction 409
12.2.1 Load transfer model 409
12.2.2 Development of on-pile force p profile 410
12.2.3 Deformation features 412
12.3 Elastic-plastic (EP) solutions 414
12.3.1 Normal sliding (upper rigid–lower flexible) 414
12.3.2 Plastic (sliding layer)–elastic-plastic (stable layer) (P-EP) solution 415
12.3.3 EP solutions for stable layer 417
12.4 p u -based solutions (rigid piles) 421
12.5 E-E, EP-EP solutions (deep sliding–flexible piles) 430
12.5.1 EP-EP solutions (deep sliding) 430
12.5.2 Elastic (sliding layer)–elastic (stable layer) (E-E) solution 430
12.6 Design charts 433
12.7 Case study 435
12.7.1 Summary of example study 444
12.8 Conclusion 444
13 Physical modeling on passive piles
13.1 Introduction 44713.2 Apparatus and test procedures 448
13.2.1 Salient features of shear tests 448
13.2.2 Test program 450
13.2.3 Test procedure 451
13.2.4 Determining pile response 455
13.2.5 Impact of loading distance on test results 455
13.3 Test results 456
13.3.1 Driving resistance and lateral force on frames 456
13.3.2 Response of M max , y o , ω versus w i (w f ) 460
13.3.3 M max raises (T block) 465
13.4 Simple solutions 467
13.4.1 Theoretical relationship between M max and T max 467
13.4.2 Measured M max and T max and restraining moment M oi 468
13.4.3 Equivalent elastic solutions for passive piles 470
13.4.4 Group interaction factors F m, F k, and p m 472
13.4.5 Soil movement profile versus bending moments 473
13.4.6 Prediction of T maxi and M maxi 474
13.4.6.1 Soil movement profile versus bending moments 474
13.4.7 Examples of calculations of M max 475
13.4.8 Calibration against in situ test piles 478
13.5 Conclusion 482
Acknowledgment 484
References 485
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