Erosion in Geomechanics Applied to Dams and Levees

Erosion in Geomechanics Applied to Dams and Levees......Page 1
Erosion in Geomechanics Applied to Dams and Levees......Page 2
Table of Contents......Page 4
Foreword......Page 11
Introduction......Page 13
1.1.1. A description of the overall process......Page 18
1.1.2. The four mechanisms of initiation and progression of internal erosion......Page 19
1.1.3. Concentrated leak erosion......Page 23
1.1.4. Backward erosion......Page 24
1.1.5. Contact erosion......Page 25
1.1.6. Suffusion......Page 26
et al.......Page 28
et al.......Page 29
et al.......Page 30
Cracking and hydraulic fracture due to small-scale irregularities in the foundation profile under the core......Page 31
et al.......Page 32
et al.......Page 33
Cracking due to desiccation......Page 35
et al.......Page 36
Internal erosion initiated by “canalicules? or other holes in residual soils......Page 38
1.2.3.1. The procedure......Page 40
1.2.3.2. The estimation of hydraulic shear stresses in cracks and pipes......Page 41
1.2.3.3. Erosion properties of soils in the core of embankment dams: basic principles......Page 42
1.2.3.5. Assessing the rate of development of the pipe......Page 48
1.2.3.6. Assessing whether the soil will hold a roof to a developing pipe......Page 50
1.2.4. Commentary on the state of the art and the role of laboratory testing in assessing concentrated leak erosion......Page 52
et al.......Page 39
1.3.1.1. The overall process......Page 54
1.3.2. Soils that are subject to backward erosion piping......Page 57
1.3.3.1. Terzaghi and Peck [TER 48]......Page 60
1.3.3.2. USACE simplified method......Page 61
1.3.3.3. The Netherlands experiments and design methods 1980 to 1999......Page 62
1.3.3.4. Recent research at Deltares, Delft......Page 63
1.3.3.5. Hoffmans [HOF 12b]......Page 66
1.3.3.6. Schmertmann [SCH 00] method for modeling initiation and progression of backward erosion......Page 67
1.3.4. Some field observations......Page 68
1.3.5. Global backward erosion......Page 69
1.3.6.1. Backward erosion piping......Page 70
1.3.6.2. Global backward erosion......Page 73
1.4.1. The mechanics of suffusion......Page 74
1.4.2.1. General requirements......Page 75
1.4.2.2. Some methods for assessing whether a soil is subject to suffusion......Page 77
1.4.2.3. Assessment of the largest erodible particles in suffusion......Page 85
1.4.3.2. Assessment of the flow velocity that will cause suffusion......Page 86
1.4.3.3. Assessment of the seepage gradient that will cause suffusion......Page 87
1.4.4. Commentary on the state of the art and the role of laboratory testing in assessing suffusion......Page 88
1.5.1. The mechanics of contact erosion......Page 91
1.5.2.1. Brauns, Wörman, and Den Adel methods for assessing the geometrical condition......Page 93
1.5.2.2. Methods for assessing the critical hydraulic conditions......Page 95
1.5.3.1. Hydraulic criteria......Page 99
1.5.4. Commentary on the state of the art and the role of laboratory testing in assessing contact erosion......Page 100
1.6. Bibliography......Page 102
2.1. Introduction......Page 117
2.2.1. Typical conditions of occurrence......Page 119
2.2.2. Specific nature of CE......Page 123
2.3. At sample scale: quantification of the CE threshold and kinetics......Page 126
2.3.1. Influence of geometry on the occurrence of CE......Page 127
2.3.2.1. Test conditions of CE......Page 128
2.3.2.2. Threshold for the occurrence of CE......Page 131
2.3.2.3. Influence of cohesion......Page 136
2.3.2.4. CE kinetics......Page 138
2.3.3. Inverse configuration......Page 145
2.3.4. Summary......Page 149
2.4. At pore scale: local hydrodynamics of CE and statistical modeling......Page 150
2.4.1.1. Local probe inside a model configuration of CE......Page 151
2.4.1.2. Characterization of velocities in the porous layer......Page 153
2.4.1.3. Characterization of shear stresses in the porous layer......Page 155
2.4.2.1. Average shear stress and critical threshold of CE......Page 159
2.4.2.2. Spatial variability and impact on the CE threshold......Page 164
2.4.2.3. Modeling CE statistically......Page 169
2.4.3. Contribution made by the local scale study......Page 174
2.5.1. Reasons for a study at this scale......Page 178
2.5.2. Description of the experimental rig and instrumentation......Page 179
2.5.3.2. Typical results with the layer geometry......Page 183
2.5.3.3. Typical results in the slope geometry......Page 185
2.5.4.1. Phase 1: initiation......Page 188
2.5.4.3. Phase 3: progression......Page 189
2.5.4.4. Phase 4: interaction with the geometry......Page 191
2.5.5. Scale effect......Page 192
2.6. Conclusion and outlook......Page 195
2.6.1. Description of CE mechanisms......Page 196
2.6.2.1. Responses that are emerging......Page 198
2.6.2.2. Open questions......Page 200
2.7. Bibliography......Page 202
3.1. Introduction......Page 208
3.2. Phases leading to failure due to backward erosion......Page 212
3.2.1. Seepage......Page 213
3.2.2. Backward erosion ? initiation and progression......Page 214
3.2.3. Widening......Page 219
3.2.4. Failure......Page 220
3.3. Backward erosion in the laboratory ? overview and setup......Page 221
3.3.1. Overview of experimental research......Page 222
3.3.2. Setup......Page 223
3.4. Backward erosion piping in the laboratory ? erosion mechanism......Page 229
3.4.1. Single grain transport......Page 230
3.4.2 Sand boiling phase......Page 231
3.4.3. Regressive or equilibrium phase......Page 232
3.4.4. Progressive phase......Page 235
3.4.5. Which process will occur when?......Page 236
3.5.1. Initiation of backward erosion piping......Page 241
3.5.2. Progression of backward erosion piping......Page 249
3.5.3. Progression of pipes for vertical seepage paths......Page 255
3.6. Analysis tools......Page 260
3.6.1. Initiation of the pipe......Page 261
3.6.2. Progression of the pipe......Page 265
3.6.3. Progression for structures......Page 271
3.6.4. Summary......Page 273
3.7.1. Scale effects......Page 274
3.7.2. Heterogeneity......Page 277
3.7.3. Uncertainties......Page 278
3.9. Bibliography......Page 279
4.1. Introduction......Page 285
4.2.1. Assumptions......Page 289
4.2.2. The model for pipe flow with erosion......Page 290
4.2.3. The singular head loss factor......Page 292
4.2.4. The momentum loss factor......Page 293
4.2.5. Characteristic values......Page 294
4.2.6. Closed-form solution in the case of a constant pressure drop......Page 295
4.2.7. Closed-form solution in the case of a constant flow rate......Page 296
4.3.1. The HET apparatus......Page 297
4.3.2. Preparation of the specimen......Page 299
4.3.2.1. Remolded sample......Page 300
4.3.2.2. Intact samples......Page 301
4.3.3. Determination of the final hole diameter......Page 302
4.4.1. Determination of the pipe radius and the wall shear stress......Page 303
4.4.2. Determination of the friction coefficient......Page 305
4.4.3. Determination of the head loss coefficient......Page 306
4.4.5. Examples of results......Page 308
4.4.6. Slaking at upstream or downstream faces of sample of HET......Page 310
4.5.1. A simplified approach......Page 313
4.5.2. Onset of erosion in the pipe......Page 315
4.5.3. Visual detection of the leak......Page 316
4.5.4. Enlargement of the pipe......Page 317
4.6.1. Order of magnitude on case studies......Page 321
4.6.2. A model for dam- and levee-break due to concentrated leak erosion......Page 325
4.6.3. Application to the failure of a homogeneous moraine dam by piping......Page 327
4.6.4. Model analysis......Page 331
4.7.1. The probabilistic approach......Page 333
4.7.2. The probability density function of the stress ratio......Page 335
4.7.3. Probabilistic description of erosion......Page 337
4.7.4. Order of magnitude of the relative intensity of the shear stress fluctuations......Page 339
4.7.5. Order of magnitude of the coefficient of variation of the soil critical stress......Page 340
4.7.6. A stochastic erosion law for cohesive soils......Page 341
4.8.1. Comment on the friction coefficient......Page 343
4.8.2. Comment on the linearity of the erosion law......Page 347
4.9. Bibliography......Page 349
5.1. Introduction......Page 356
5.2. Definitions of soil erosion properties and the relationships between them......Page 357
5.3.1. Effect of testing methods on erosion rate......Page 359
5.3.2. Effect of testing methods on critical shear stress 쐀挀......Page 363
5.3.3. Correlation between critical shear stress and erosion rate index......Page 366
5.4.2. Assessment of rates of erosion from JET and large-scale laboratory tests......Page 368
5.5.1. General trends......Page 371
5.5.2. Relationship to soil classification......Page 372
5.6.1. Relationship to compaction parameters......Page 373
5.6.2. Relationship to degree of saturation after compaction......Page 377
5.7.1. Effects of dispersivity on erosion rate and critical shear stress......Page 379
5.7.2. Effects of slaking on erosion rate and critical shear stress......Page 382
5.8.1. Modification by lime......Page 384
5.9. Bibliography......Page 389
List of Authors......Page 395
Index......Page 398