Theory and Practice of Pile Foundations

Contents

List of Figures 
Preface 
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  Introduction 
2.2  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)  47
3.1.1  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  105
4.2  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  147
5.1.1  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  177
6.2  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  201
7.2  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  229
8.2  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  277
9.2   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  Contents
10.2  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  375
11.2  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  405
12.1.1  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  447
13.2   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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