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Title Page
Contents
List of Symbols and Abbreviations 12
Chapter 1. Introduction 16
1.1. Background 16
1.2. Research Methodology 19
1.3. Objectives 22
1.4. Scope of Study 22
1.5. Significance of Study 22
1.6. Limitations of Study 23
1.7. Organization 24
Chapter 2. Literature Review 26
2.1. General 26
2.2. Slope Stability in Term of Seepage Hazard 27
2.3. Slope Stability in Term of Rainfall Hazard 29
2.3.1. Rainfall Duration 32
2.3.2. Rainfall Pattern 33
2.4. Slope Stability in Term of Drawdown Condition 37
2.4.1. Importance of Reservoir Slope Stability Analysis 37
2.4.2. Controlling Factors for Reservoir Slope Stability 38
2.4.3. Saturated-Unsaturated Drawdown Analysis 39
2.5. Hydraulic Conductivity 42
2.5.1. Isotropic Hydraulic Conductivity 42
2.5.2. Anisotropic Hydraulic Conductivity 44
2.6. Probabilistic Assessment of Slope Stability 48
2.6.1. Deterministic and Probabilistic Approach 48
2.6.2. Randomness in Soil Properties 50
2.6.3. Monte-Carlo Simulation 53
2.7. Numerical Modeling to Analyze Saturated-Unsaturated Slope Stability Problem 55
2.7.1. Importance of Numerical Modeling 55
2.7.2. The Role of Geo-Studio in Saturated- Unsaturated Soil Slope Problem 56
Chapter 3. Fundamental Concepts 61
3.1. General 61
3.2. Saturated-Unsaturated Soil 62
3.2.1. Emergence and Application of Unsaturated Soil Mechanics 62
3.2.2. Characterization of Saturated-Unsaturated Soil 66
3.2.3. Soil Suction and Air Pressure 68
3.2.4. Soil Water-Content and Suction Relationship 70
3.2.5. The Permeability-Suction Relationship 77
3.2.6. Evaluation of Characteristic Curves 79
3.2.7. Water Flow in Saturated-Unsaturated Soil 83
3.2.8. Stress-State Variable in Saturated-Unsaturated Soil 85
3.2.9. Shear-Strength of Saturated-Unsaturated Soil 86
3.2.10. Slope Stability in Term of Saturated-Unsaturated Seepage 90
3.3. Rainfall and Drawdown Boundary Conditions 93
3.4. Description of Anisotropic Conductivity 96
3.5. Slope Stability Analysis 99
3.5.1. Basic Principles of Limit Equilibrium 99
3.5.2. Methods of Limit Equilibrium 102
3.5.3. Morgenstern-Price Method 104
3.5.4. Critical Slip Surface in Slope/W 106
3.6. Probabilistic Design in Slopes 109
3.6.1. Basics of Probabilistic Approach 109
3.6.2. Methods for Probabilistic Slope Stability Analysis 113
3.6.3. Reliability Analysis with Monte-Carlo Simulation 114
Chapter 4. Applications 117
4.1. General 117
4.1.1. Arrangement 117
4.1.2. Important Points 119
4.2. Case Study 1 121
4.2.1. Introduction 121
4.2.2. Geometry and Finite Element Model 121
4.2.3. Material Strength Properties and Random Variables 124
4.2.4. Saturated-Unsaturated Seepage Analysis 125
4.2.5. Slope Stability Analysis 131
4.2.6. Pore-Water Pressure and Volumetric Water Content 132
4.2.7. Results of Slope Stability 138
4.2.8. Conclusion 141
4.3. Case Study 2 142
4.3.1. Introduction 142
4.3.2. Geometry and Finite Element Model 142
4.3.3. Material Properties and Random Variables 144
4.3.4. Saturated-Unsaturated Seepage Analysis 144
4.3.5. Rainfall Pattern 147
4.3.6. Slope Stability Analysis 149
4.3.7. Result and Discussion 149
4.3.8. Conclusion 154
4.4. Case Study 3 155
4.4.1. Introduction 155
4.4.2. Geometry and Finite Element Model 155
4.4.3. Material Properties and Random Variables 157
4.4.4. Drawdown Condition 157
4.4.5. Saturated-Unsaturated Seepage Analysis 157
4.4.6. Slope Stability Analysis 158
4.4.7. Result and Discussion 161
4.4.8. Conclusion 168
4.5. Case Study 4 169
4.5.1. Introduction 169
4.5.2. Geometry and Finite Element Model 170
4.5.3. Material Properties and Random Variables 170
4.5.4. Soil Curves for Seepage Analysis 170
4.5.5. Head Difference 170
4.5.6. Slope Stability Analysis 171
4.5.7. Analyses Results 175
4.5.8. Discussion 177
4.5.9. Conclusion 183
Chapter 5. Conclusions and Recommendations 184
5.1. Summary 184
5.2. Conclusions 185
5.3. Recommendations 187
Bibliography 188
요약 198
Abstract 200
Table 2.1: Coefficient of variation of some soil properties 51
Table 2.2: Typical coefficient of variation (c.o.v) for the cohesion 52
Table 2.3: Typical coefficient of variation (c.o.v) for angle of friction 52
Table 3.1: Summary of LE methods 103
Table 4.1: Material strength properties 125
Table 4.2: SWCC properties and saturated hydraulic conductivity for weathered soil 127
Table 4.3: Material properties along with probabilistic characteristics 145
Table 4.4: SWCC properties and saturated hydraulic conductivities 145
Table 4.5: Soil properties along with probabilistic characteristics 159
Table 4.6: The applied drawdown condition 159
Table 4.7: SWCC properties and hydraulic conductivities 159
Table 4.8: Material properties along with probabilistic characteristics 173
Table 4.9: Head difference used in case study 173
Figure 1.1: An overview of case studies presented in research work. 20
Figure 1.2: Flowchart for research methodology. 21
Figure 2.1: Variation in pore water pressure distribution with depth. 31
Figure 2.2: Three drawdown modes for slope stability analysis. 41
Figure 2.3: General framework for probabilistic design. 49
Figure 3.1: Map showing extremely arid, arid and semi-arid regions of the world. 64
Figure 3.2: Classes of unsaturated soil. 65
Figure 3.3: The distribution of subsurface water 67
Figure 3.4: Penetration of air-water interface into soil 73
Figure 3.5: Schematic diagram of hypothetical porous medium. 74
Figure 3.6: Typical form of the SWCC 75
Figure 3.7: SWCCs for some Dutch soils 76
Figure 3.8: Typical suction-dependent hydraulic conductivity function. 78
Figure 3.9: Soil water characteristic curves and permeability suction curves. 82
Figure 3.10: Variation of shear strength with matric suction 89
Figure 3.11: Effect of climatic conditions on pore-water pressure profiles in slope. 92
Figure 3.12: Some common rainfall patterns 94
Figure 3.13: Assigned rainfall conditions on the slope surface in Seep/W 94
Figure 3.14: Head versus time function for reservoir drawdown 95
Figure 3.15: Definition of hydraulic conductivity matrix parameters. 98
Figure 3.16: Various definitions of the factor of safety (FS) 101
Figure 3.17: Typical interslice force functions used in the Morgenstern-Price method. 107
Figure 3.18: Grid and radius option used to search for circular critical slip surface. 108
Figure 3.19: Probability density function of the factor of safety, Fs, and probability of failure, Pf. 110
Figure 3.20: Relationship between reliability index and the probability of failure. 112
Figure 3.21: Flow chart of Monte Carlo method 116
Figure 4.1: (a) Geometry and; (b) FE discretization of single cut-slope 122
Figure 4.2: (a) Geometry and; (b) FE discretization of multi cut-slope 123
Figure 4.3: Soil water characteristic curve for weathered soil. 128
Figure 4.4: Hydraulic conductivity curve of weathered soil for different anisotropic ratios. 130
Figure 4.5: Initial condition 133
Figure 4.6: Single cut-slope 134
Figure 4.7: Multi cut-slope 135
Figure 4.8: Reliability indexes 140
Figure 4.9: (a) Geometry and; (b) FE discretization of multi cut-slope. 143
Figure 4.10: Soil curves 146
Figure 4.11: Rainfall patterns 148
Figure 4.12: Initial condition 150
Figure 4.13: Slope reliability indexes in term of rainfall 151
Figure 4.14: (a) Average volumetric-water content and; (b) average porewater pressure profiles for soil 1 (total rainfall ＝ 2.7m). 153
Figure 4.15: Dam embankment 156
Figure 4.16: Soil curves 160
Figure 4.17: Initial reliability index for three kinds of soils at different anisotropic ratios. 162
Figure 4.18: Flow-net diagrams at reservoir level of 17.5 m 162
Figure 4.19: Pore-water pressure at the slice slip surface at different anisotropic ratios 163
Figure 4.20: Reliability indexes in term of different drawdown ratio 165
Figure 4.21: Pore-water pressure profiles at different drawdown ratios 167
Figure 4.22: (a) Geometry and; (b) FE discretization of dam with toe drain. 172
Figure 4.23: (a) Geometry and; (b) FE discretization of dam without toe-drain. 172
Figure 4.24: Soil curves 174
Figure 4.25: Seepage face in term of head difference 176
Figure 4.26: Reliability index in term of head difference for upstream slope of dam 176
Figure 4.27: Flow-net diagrams for dam with toe-drain at same elevation in reservoir 179
Figure 4.28: Flow-net diagrams for dam with toe-drain at same elevation in reservoir 180
Figure 4.29: Points for evaluation of equi-potential head 181
Figure 4.30: Values of equipotential head at different points of Fig. 4.29 in term of anisotropic ratio. 182
Figure 4.31: Pore-water pressure at the slice surface at different anisotropic ratio for soil 1 182
초록보기 더보기
사면안정은 지반공학에서 가장 많이 다루는 문제 중 하나이다. 고전적인 사면안정 해석은 흙이 포화상태라는 가정하에 해석방법을 제안하고 있다. 하지만 대부분의 흙들은 풍화상태로 잔류되어 있기 때문에 불포화상태로 주로 존재하고 있으며, 상기 고전적인 해석방법으로는 아주 정확한 결과를 기대하기 어렵다. 특히 불포화상태에서의 흙의 거동특성은 매우 큰 비선형성을 보이기 때문에 정확한 간극수압 상태를 예측하는 것은 포화-불포화 상태에서의 사면문제에서 매우 중요한 요소이다. 그리고 상기 언급한 포화-불포화상태에서의 사면안정 해석을 위해 유한요소법 같은 수치해석이나 한계상태평형법과 같은 고전적 이론 해법을 사용한다.
확률론적 접근방법은 불확실성이 상대적으로 많은 지반공학, 특히 사면 안정해석에서 체계적인 해법을 제공한다. 사면안정의 확률론적 접근에서 불확실성들은 설계의 신뢰도와 정량적인 관계가 있다. 따라서 위험도 기반의 설계절차는 사면 안정의 허용 위협 기준을 결정하기 위한 해석법으로 유용하게 사용될 수 있다. 본 연구에서는 사면안정 해석결과를 확률론적 방법을 사용해 신뢰성 지수를 산출한다. 해석결과의 확률분포를 산출하기 위해 고전적 해법에 사용되는 매개변수들의 분포를 적용하여 몬테카를로 시뮬레이션을 수행한다. 해석결과의 분포는 파괴확률과 사면안정의 신뢰도로 정의된다.
이 연구의 목적은 강우량과 수위저하에 따른 포화-불포화 상태의 사면 안정을 확률론적으로 정량화하는 것이다. 예측 가능한 이런 외부 요인의 영향은 각각 다른 기하학적, 수문학적 특성을 가진 사면 재료를 이용한 예제를 통하여 연구하였다. 예제들은 이방성 투수조건 하에, 강우의 패턴, 비온 뒤 정상상태 및 일시적인 수위저하 등의 주제를 다루었다. 이런 서로 다른 매개변수가 간극수압과 사면안정성에 미치는 영향을 분석하여 결과를 도표의 형태로 나타내었다.
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