Hydraulic fracturing in earth-rock fill dam

There have been a number of well-studied cases in which dams have failed or been damaged by concentrated leaks for no apparent cause. In some of these experiences, investigators concluded that differential settlement cracks were the probable causes, even though no cracks were seen on the surface. In these examples, it was not determined whether the crack was open before the reservoir filled or whether it might have opened afterward. In several unsolved problems on the safety of the earth-rock fill dam, the problem of hydraulic fracture in the soil core of the earth-rock fill dam is one that is widely paid attention by designers and researchers. Hydraulic fracturing is generally considered as a key cause which may induce the leakage of the dam during first filling.

In this extensive book, a new numerical simulate method is suggested. The method is based on the conventional two-dimensional finite element technique, and the theoretical formulations to calculate energy release rate using virtual crack extension method. The influence factors on convergence of calculated J integral are investigated. The accuracy of the calculated J integral is verified by analysing the three typical problems in Fracture Mechanics, in which propagation of crack may follow mode I, mode II and mixed mode I-II respectively. Using the new numerical method, the factors affecting the occurrence of hydraulic fracturing in the earth-rock fill dam are investigated. The investigating results indicate that increasing any of the Young's modulus, the Poisson's ratio and the density of the core soil is helpful to reduce the likelihood of the occurrence of hydraulic fracturing. The likelihood of the occurrence of hydraulic fracturing increases with increasing the water level or the crack depth. The lower part of the dam core is the zone in which the phenomenon of hydraulic fracturing may be induced easily. As an example to analyse the ability of earth-rock fill dam to resist hydraulic fracturing, the Nuozhadu Dam located in Western China is analysed.

Presents a systematic and comprehensive study of hydraulic fracturing, original in its concentration of core soil problems Focuses on the problem of hydraulic fracturing in earth-rock fill dams from three aspects; conditions and mechanisms of hydraulic fracturing, criterion of hydraulic fracturing, and numerical method on hydraulic fracturing Examines advanced laboratory soil testing, application of numerical methods and field testing/monitoring, all needed for a better understanding of hydraulic fracturing in earth/rock fill dams Provides an essential reference in an area of scarce research in this field, and the need in high earth dam construction in developing countries is pressing

Ideal for researchers in Hydraulic and Geotechnical Engineering Fields; Students on Masters or PhD courses; as well as Designers and Constructors in Hydraulic and Geotechnical Engineering Fields.

Author Notes

Jun-Jie Wang, PhD, Professor, National Engineering Research Center for Inland Waterway Regulation, Chongqing Jiaotong University, Chongqing, P.R. China
Professor Wang achieved hisPhD in Geotechnical Engineering in 2005 from Hohai University, Nanjing, P. R. China.'He currently teaches in the following areas: Engineering Geology, Hydrogeology, Soil Mechanics and Foundation Engineering, Seepage Mechanics, Rock Mechanics, and?Survey of Engineering Geology.' Professor Wang has written numerous journals papers on his subject and has patented many designs and inventions to assist in his research.

About the Author	p. xi
Preface	p. xiii
Acknowledgments	p. xvii
Nomenclature	p. xix
1 Introduction	p. 1
1.1 Types of Embankment Dam	p. 1
1.2 Hydraulic Fracturing	p. 3
1.3 Failure of the Teton Dam	p. 5
1.4 Erosion Damage of the Balderhead Dam	p. 9
1.5 Leakage of the Hyttejuvet Dam	p. 13
1.6 Self-Healing of Core Cracks	p. 17
1.7 Technical Route for Present Study	p. 18
1.8 Summary	p. 20
References	p. 20
2 Review of Literature	p. 23
2.1 Introduction	p. 23
2.2 Theories of Hydraulic Fracturing	p. 23
2.2.1 Theories Based on Circular Cavity Expansion Theory	p. 24
2.2.2 Theories Based on Spherical Cavity Expansion Theory	p. 26
2.2.3 Theories Based on True Triaxial Stress State Analyses	p. 27
2.2.4 Empirical Formulas	p. 31
2.2.5 Theories Based on Fracture Mechanics	p. 34
2.3 Laboratory Experimental Studies on Hydraulic Fracturing	p. 38
2.3.1 Cylindrical Sample	p. 38
2.3.2 Rectangular Sample	p. 39
2.4 Field Testing Studies of Hydraulic Fracturing	p. 40
2.5 Model Testing Studies of Hydraulic Fracturing	p. 41
2.6 Numerical Simulations of Hydraulic Fracturing	p. 42
2.7 Analysis Method for Hydraulic Fracturing	p. 45
2.8 Summary	p. 46
References	p. 47
3 Conditions and Mechanisms of Hydraulic Fracturing	p. 51
3.1 Introduction	p. 51
3.2 Conditions for Hydraulic Fracturing	p. 52
3.2.1 Crack Located at the Upstream Face of Core	p. 52
3.2.2 Low Permeability of Core Soil	p. 55
3.2.3 Rapid Impounding	p. 56
3.2.4 Unsaturated Soil Core	p. 56
3.3 Mechanical Mechanism of Hydraulic Fracturing	p. 61
3.4 Modes of Fracture in Fracture Mechanics	p. 62
3.5 Summary	p. 65
References	p. 66
4 Fracture Toughness and Tensile Strength of Core Soil	p. 69
4.1 Introduction	p. 69
4.2 Tested Soil	p. 71
4.3 Testing Technique on Fracture Toughness	p. 72
4.3.1 Testing Method	p. 72
4.3.2 Apparatus	p. 73
4.3.3 Testing Procedures	p. 75
4.3.4 Testing Program	p. 76
4.4 Testing Results on Fracture Toughness	p. 77
4.4.1 Suitability of Linear Elastic Fracture Mechanics	p. 11
4.4.2 Influence Factors on Fracture Toughness	p. 80
4.5 Testing Technique on Tensile Strength	p. 82
4.5.1 Testing Method and Apparatus	p. 84
4.5.2 Calculation of Tensile Strength	p. 84
4.5.3 Testing Procedures	p. 85
4.5.4 Testing Program	p. 86
4.6 Testing Results on Tensile Strength	p. 86
4.6.1 Water Content	p. 86
4.6.2 Dry Density	p. 88
4.6.3 Preconsolidation Pressure	p. 89
4.7 Relationship between Fracture Toughness and Tensile Strength	p. 89
4.8 Discussions	p. 90
4.8.1 Soils from References	p. 90
4.8.2 Rocks from References	p. 93
4.9 Summary	p. 94
References	p. 95
5 Fracture Failure Criteria for Core Soil under I-II Mixed Modes	p. 99
5.1 Introduction	p. 99
5.2 Experimental Technique	p. 101
5.2.1 Loading Assembly	p. 102
5.2.2 Calculation Theory	p. 102
5.2.3 Testing Procedures	p. 104
5.2.4 Test Program	p. 104
5.3 Testing Results	p. 105
5.4 Fracture Failure Criteria	p. 108
5.5 Discussions	p. 111
5.5.1 Testing Technique	p. 111
5.5.2 Failure Criteria	p. 111
5.6 Summary	p. 115
References	p. 116
6 Hydraulic Fracturing Criterion	p. 121
6.1 Introduction	p. 121
6.2 Failure Criterion	p. 121
6.2.1 Simplification of a Crack	p. 122
6.2.2 Criterion	p. 122
6.3 Cubic Specimen with a Crack	p. 124
6.3.1 Calculation of K I	p. 126
6.3.2 Calculation of K II	p. 126
6.3.3 Calculation of(K 2 I + K 2 II ) 0.5	p. 127
6.3.4 Dangerous Crack Angle	p. 128
6.4 Core with a Transverse Crack	p. 128
6.4.1 Calculation of K I	p. 131
6.4.2 Calculation of K II	p. 131
6.4.3 Calculation of(K 2 I + K 2 II ) 0.5	p. 132
6.4.4 Dangerous Crack Angle	p. 133
6.5 Core with a Vertical Crack	p. 135
6.6 Strike-Dip of Easiest Crack Spreading	p. 137
6.7 Summary	p. 142
References	p. 143
7 Numerical Method for Hydraulic Fracturing	p. 145
7.1 Introduction	p. 145
7.2 Theoretical Formula	p. 146
7.2.1 Failure Criterion for Hydraulic Fracturing	p. 146
7.2.2 Path Independent J Integral	p. 147
7.2.3 Virtual Crack Extensions Method	p. 148
7.2.4 Calculation of the J Integral	p. 149
7.3 Numerical Techniques	p. 150
7.3.1 Virtual Crack	p. 150
7.3.2 Finite Element Model	p. 151
7.3.3 Water Pressure Applied on the Crack Face	p. 151
7.3.4 Simulation of Hydraulic Fracturing	p. 152
7.4 Numerical Investigation	p. 152
7.4.1 Finite Element Model	p. 152
7.4.2 Virtual Crack Depth	p. 155
7.4.3 Mechanical Parameters of Crack Material	p. 155
7.5 Numerical Verification	p. 156
7.5.1 Mode I Crack	p. 156
7.5.2 Mode II and Mixed Mode I-II Cracks	p. 158
7.6 Summary	p. 161
References	p. 161
8 Factors Affecting Hydraulic Fracturing	p. 165
8.1 Introduction	p. 165
8.2 Factors Affecting Stress Arching Action	p. 166
8.2.1 Influence of Material Properties	p. 167
8.2.2 Influence of Dam Structure	p. 171
8.3 Relation between Hydraulic Fracturing and Arching Action	p. 175
8.4 Factors Affecting Hydraulic Fracturing	p. 177
8.4.1 Analyzing Method	p. 178
8.4.2 Influence of Water Level	p. 180
8.4.3 Influence of Crack Depth	p. 181
8.4.4 Influence of Crack Position	p. 182
8.4.5 Influence of Core Soil Features	p. 184
8.5 Summary	p. 189
References	p. 190
9 Self-Healing of a Core Crack	p. 193
9.1 Introduction	p. 193
9.2 Experimental Method and Instrument	p. 194
9.2.7 Experimental Method	p. 194
9.2.2 Experimental Instrument	p. 196
9.3 Tested Soil	p. 197
9.4 Test Program	p. 198
9.5 Results Analysis	p. 199
9.5.1 Influence of Crack Depth	p. 199
9.5.2 Influence of Grain Size	p. 199
9.5.3 Mechanism of Self-Healing	p. 203
9.6 Discussion	p. 203
9.7 Summary	p. 205
References	p. 206
10 Simulation on the Nuozhadu Dam in China	p. 209
10.1 Introduction to the Nuozhadu Dam	p. 209
10.2 Numerical Software	p. 210
10.3 Behavior of Stress-Deformation of Nuozhadu Dam	p. 214
10.3.1 Finite Element Model	p. 214
10.3.2 Material Parameters	p. 214
10.3.3 Behavior of Stress-Deformation after Construction	p. 217
10.3.4 Behavior of Stress-Deformation after Filling	p. 220
10.4 Analysis Method on Hydraulic Fracturing of the Nuozhadu Dam	p. 223
10.4.1 Analysis Method	p. 223
10.4.2 Material Parameters	p. 225
10.4.3 Finite Element Model	p. 225
10.4.4 Schemes Analyzed	p. 227
10.5 Hydraulic Fracturing in Horizontal Cracks	p. 227
10.6 Hydraulic Fracturing in Vertical Cracks	p. 229
10.7 Summary	p. 231
References	p. 231
Index	p. 235

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