On the delayed failure of geotechnical structures in low permeability ground (eBook)

On the delayed failure of geotechnical structures in low permeability ground 1
Vorwort 5
Acknowledgments 6
Abstract 7
Zusammenfassung 9
Table of contents 12
1. Introduction 14
1.1 Problem definition 14
1.1.1 Delayed failure 14
1.1.2 Stand-up time 16
1.2 Current state of research 18
1.2.1 Numerical studies 18
1.2.2 Field tests and physical modelling 20
1.3 Objectives and structure of the thesis 20
1.4 Computational method 22
2. Structural softening 24
2.1 Introduction 24
2.2 Reduction factor 26
3. Manifestations of delayed failure 30
3.1 Introduction 30
3.2 Problem setup and computational model 31
3.3 Mohr-Coulomb material 31
3.3.1 Stability under undrained or drained conditions 31
3.3.2 Coupled analysis for dilatant plastic behaviour 36
3.3.2.1 Displacement rate 36
3.3.2.2 Pore pressure, stress and strain development 39
3.3.2.3 Comments on the steady state 39
3.3.2.4 On the possible effect of an increase in permeability 40
3.3.2.5 Estimating stand-up time 42
3.3.3 Coupled analysis for isochoric plastic behaviour 43
3.3.3.1 Displacement rate 43
3.3.3.2 Development of pore pressures, strains and stresses 45
3.3.3.3 Reason of numerical instability 47
3.3.3.4 Estimating stand-up time 47
3.3.3.5 Influence of the loading on the bottom boundary 47
3.4 Coupled analysis for Modified Cam Clay material 49
3.4.1 Assumptions 49
3.4.2 Development of pore pressures, strains and stresses 51
3.4.3 Effect of OCR on stand-up time 56
3.5 Conclusions 57
4. Mesh dependency 58
4.1 Introduction 58
4.2 Underwater vertical cut 59
4.2.1 Inclination of the sliding surface 60
4.2.2 Critical strength parameters 62
4.2.3 Stand-up time 63
4.3 Biaxial problem 65
4.3.1 Problem definition 65
4.3.2 Analytical solution for the estimation of the stand-up time 66
4.3.2.1 Derivation 66
4.3.2.2 Upper and lower limit of the stand-up time 69
4.3.3 Numerical estimation of the stand-up time 70
4.3.3.1 Computational model 70
4.3.3.2 Shear band propagation mechanism 70
4.3.3.2.1 Elastic behaviour at early excess pore pressure dissipation stage 70
4.3.3.2.2 Onset of yielding 75
4.3.3.2.3 The numerical identification of structural softening 77
4.3.3.2.4 The stress re-distribution process 79
4.3.3.3 Stand-up time 81
4.3.3.4 Influence of the element size on the stand-up time 82
4.3.3.4.1 Numerical results 82
4.3.3.4.2 Interpretation 87
4.3.3.4.3 The effect of the discretization on the propagation speed 87
4.3.3.4.4 Stand-up time estimation for very thin shear bands 91
4.4 Conclusions 92
5. Uniaxial loading tests 93
5.1 Introduction 93
5.2 Experimental study 94
5.2.1 Material and methods 94
5.2.1.1 Specimen preparation 94
5.2.1.2 Installation of pore pressure transducers 94
5.2.1.3 Testing device and procedure 100
5.2.1.4 Material parameters 102
5.2.2 Results 106
5.2.2.1 Pore pressure evolution during the pre-test phase 106
5.2.2.2 Underwater tests 108
5.2.2.3 Tests executed under water vapour 111
5.3 Numerical study 113
5.3.1 Computational model 113
5.3.2 Computational steps 113
5.3.2.1 MCC model 113
5.3.2.2 MC model 114
5.3.3 MCC model results 114
5.3.3.1 Simulation results for the underwater test 114
5.3.3.2 Simulation results for the test under water vapour 120
5.3.4 Underwater test interpretation by MC model 125
5.4 Conclusions 127
6. Centrifuge tests 129
6.1 Introduction 129
6.2 Centrifuge modelling 131
6.2.1 Material and methods 131
6.2.1.1 Scaling laws and model dimensions 131
6.2.1.2 Model preparation 132
6.2.1.3 Instrumentation 133
6.2.1.4 Test procedure 134
6.2.1.5 Determination of the material parameters 135
6.2.1.5.1 Theoretical estimation of the effective cohesion 136
6.2.1.5.2 Cohesion estimation based upon the results of T-bar penetrometer tests 139
6.2.1.5.3 Selection of the effective cohesion to be used in the MC model 142
6.2.2 Experimental results 142
6.3 Limit equilibrium analysis 146
6.4 Numerical modelling 148
6.4.1 Computational model 148
6.4.2 Simulation procedure 149
6.4.2.1 MC model 149
6.4.2.2 MCC model 150
6.4.3 Results 151
6.4.3.1 MC model 151
6.4.3.2 MCC model 154
6.5 Mesh dependency 159
6.6 Conclusions 161
7. Stand-up time of tunnel face 162
7.1 Introduction 162
7.2 Computational model 162
7.3 Undrained and drained tunnel face stability 165
7.3.1 Numerical investigation 165
7.3.2 Comparison with analytical solutions 168
7.4 Tunnel face stability under transient conditions 169
7.5 On the transient tensile failure of the ground 173
7.6 On some factors influencing stand-up time 176
7.6.1 Cohesion 176
7.6.2 Friction angle 178
7.6.3 In situ horizontal effective stress 180
7.6.4 Depth of cover 182
7.7 Design diagrams 184
7.8 Application example 191
7.9 The influence of the support pressure on the stand-up time 192
7.10 Critical advance rate 193
7.11 Conclusions 196
8. Conclusions and outlook 197
Appendix A. Publications from the present thesis 199
Appendix B. Water retention curve 200
Appendix C. List of symbols 204
References 207