Bifurcations and Instabilities in Geomechanics: Proceedings of the International Workshop, IWBI 2002, Minneapolis, Minnesota, 2-5 June 2002

Section 1. Critical states and bifurcation conditions......Page 8
1 INTRODUCTION......Page 9
2 CONDITIONS FOR LOSS OF CONTROL ‘LATENT INSTABILITY’......Page 11
3 EXAMPLES OF LOSS OF CONTROL IN THE HARDENING REGIME......Page 13
4 SOFTENING AND LOSS OF CONTROL IN OEDOMETRIC TESTS......Page 16
5 CONCLUSIONS......Page 20
REFERENCES......Page 21
1 INTRODUCTION......Page 34
2 WHAT ARE COMPACTION BANDS?......Page 35
3 WHY DO COMPACTION BANDS FORM?......Page 36
4.1 Axisymmetric Compression......Page 37
4.2 General Deformation States......Page 39
5 CONCLUDING DISCUSSION......Page 41
REFERENCES......Page 43
Section 2. Instabilities and discrete systems......Page 58
1 INTRODUCTION......Page 59
2 A STATISTICAL-THERMODYNAMIC MODEL OF CONTACT FORCES......Page 61
2.1 Isotropic monodisperse assemblies of frictionless spheres......Page 63
3 COMPARISON WITH EXPERIMENT AND SIMULATION......Page 64
4 CONCLUSIONS......Page 65
REFERENCES......Page 66
1 INTRODUCTION......Page 67
2.1 Drained triaxial compressions......Page 68
2.2 Undrained triaxial compressions......Page 69
2.3 Generalisation : cones of unstable directions......Page 70
3.1 The utilized discrete material......Page 71
3.2 The utilized discrete element method......Page 73
4 SLOPE FAILURE IN AN ACTIVE STATE......Page 75
5 SLOPE FAILURE BY ROTATION......Page 77
6 CONCLUSIONS......Page 79
REFERENCES......Page 80
INTRODUCTION......Page 81
Experimental Techniques......Page 82
GREEN’S FUCNTION MEASUREMENTS......Page 84
STATISTICAL PROPERTIES OF DENSE SLOWLY SHEARED SYSTEMS......Page 86
CONCLUSIONS......Page 93
REFERENCES......Page 94
1 INTRODUCTION......Page 95
2.1 Non Smooth Contact Dynamics......Page 96
2.2 The experiment......Page 97
3 MACROSCOPIC FRICTIONAL PROPERTIES......Page 98
4 THE GRANULAR TEXTURE......Page 99
4.2 Evolution of the partial stress tensors......Page 100
5 MOBILIZATION OF FRICTION: THE CRITICAL CONTACTS......Page 101
5.1 Intermittency and local instabilities......Page 102
5.2 Spatial correlations of the critical contacts......Page 103
5.3 The local stress state......Page 105
6 THE CRITICAL CONTACTS AND THE TEXTURE: A SCENARIO FOR THE DESTAB1LIZAT10N PROCESS......Page 106
7 CONCLUSION......Page 107
REFERENCES......Page 108
Section 3. Modeling and localization......Page 109
1 INTRODUCTION......Page 110
2 LIMIT EQUILIBRIUM MODEL......Page 112
3 FINITE ELEMENT ANALYSIS......Page 116
REFERENCES......Page 119
INTRODUCTION......Page 121
MATHEMATICAL PRELIMINARIES......Page 122
PLASTICITY MODEL......Page 123
EVOLUTION OF FRICTION AND DILATANCY......Page 124
SIMULATION OF SHEAR BAND INITIATION......Page 125
INTERNAL LENGTH SCALE AND NUMERICAL SHEAR BAND THICKNESS......Page 126
A MICROMECHANICS MODEL FOR PLASTIC FLOW......Page 128
Modeling of heterogeneous porosity-distribution......Page 129
CONCLUSIONS......Page 130
REFRENCES......Page 131
1 INTRODUCTION......Page 132
2 CYCLIC SHEARING......Page 133
3 PLANE STRAIN COMPRESSION......Page 135
5 MOVEMENTS OF A RETAINING WALL......Page 141
6 CONCLUSIONS......Page 144
REFERENCES......Page 147
1 INTRODUCTION......Page 148
2.1 Stress-dilatancy with embedded fabric......Page 149
2.2 Elasto-plastic constitutive law......Page 150
2.3 Fabric evolution......Page 151
3.2 Effect of pre-shear stress-ratio......Page 152
4 SHEAR BAND ANALYSIS......Page 155
5 INFLUENCE OF FABRIC ON SHEAR BAND LOCALIZATION IN PLANE STRAIN......Page 157
6 CONCLUSIONS......Page 158
REFERENCES......Page 159
1 INTRODUCTION......Page 160
2.1 Inherently isotropic material......Page 161
2.2 Initially transversely isotropic material......Page 163
3 LOCALIZATION CRITERION......Page 164
3.1 Bifurcation analysis......Page 166
REFERENCES......Page 169
Section 4. Experimental studies......Page 171
1 INTRODUCTION......Page 172
2 SOIL TESTED AND EXPERIMENTAL SETUP......Page 173
3.1 Instability of loose sand under undrained conditions......Page 175
3.2 Instability of loose sand under drained conditions......Page 177
3.3 Instability of dense sand under non-undrained conditions......Page 178
4 CLASSIFICATION OF INSTABILITY......Page 181
4.1 Runaway instability......Page 182
4.4 Runaway versus Conditional Instability......Page 185
6 PREFERENCES......Page 187
1 INTRODUCTION......Page 189
2.2 Digital Image Correlation DIC......Page 190
3 LOCAL DISPLACEMENT EVOLUTION......Page 191
4.2 Critical States......Page 194
5 SHEAR BAND UNIFORMITY......Page 197
6 SHEAR BAND THICKNESS AND INCLINATION......Page 198
8 REFERENCES......Page 201
1 INTRODUCTION......Page 203
2.1 Biaxial frame......Page 204
2.2 Specimen setup......Page 205
3 RESULTS......Page 206
3.1 Acoustic activity......Page 207
3.2 Optical microscopy......Page 209
4 DISCUSSION OF RESULTS......Page 210
5 CONCLUDING REMARKS......Page 211
REFERENCES......Page 212
Section 5. Non-local models and coupled effects......Page 213
1 INTRODUCTION......Page 214
2 THE RELATIONSHIPS AMONG THE REGULARIZING APPROACHES OF LOCALIZATION......Page 215
3 RATE-DEPENDENT DAMAGE AND DECOHESION......Page 216
4.1 The material point method......Page 221
4.2 Demonstration......Page 222
REFERENCES......Page 226
1 INTRODUCTION......Page 227
2 ELASTO-VISCOPLASTIC MODEL FOR CLAY......Page 228
3 INSTABILITY OF THE MODEL......Page 232
4.1 Effects of dilatancy......Page 235
4.3 Mesh size dependency......Page 238
5 CONCLUSIONS......Page 239
REFERENCES......Page 240
1 INTRODUCTION......Page 241
2.1 The concept of volume fractions......Page 242
2.2 Kinematical relations......Page 243
2.3 Balance relations......Page 244
2.4.1 The fluid constituents......Page 245
2.4.2 The solid constituent......Page 248
3 NUMERICAL TREATMENT......Page 249
4.1 Drainage of a soil column......Page 251
4.2 Flow through an embankment......Page 252
5 CONCLUSION......Page 254
REFERENCES......Page 255