Dam Failure Mechanisms and Risk Assessment

Foreword by Kaare Høeg xiii Foreword by Jinsheng Jia xiv Preface xvi Acknowledgements xviii About the Authors xix PART I DAM AND DIKE FAILURE DATABASES 1 1 Dams and Their Components 3 1.1 Classification of Dams 3 1.2 Constructed Embankment Dams 4 1.3 Landslide Dams 7 1.4 Concrete Gravity Dams 7 1.5 Concrete Arch Dams 8 1.6 Dikes 10 2 Statistical Analysis of Failures of Constructed Embankment Dams 11 2.1 Database of Failures of Constructed Embankment Dams 11 2.2 Failure Modes and Processes 11 2.2.1 Overtopping 16 2.2.2 Internal Erosion 17 2.3 Common Causes of Embankment Dam Failures 19 2.4 Failure of Different Types of Embankment Dams 21 2.4.1 Analysis of Homogeneous and Composite Earthfill Dams 23 2.4.2 Analysis of Earthfill Dams with Corewalls 23 3 Statistical Analysis of Failures of Landslide Dams 25 3.1 Database of Failures of Landslide Dams 25 3.1.1 Locations of Landslide Dams 25 3.1.2 Formation Times of Landslide Dams 26 3.1.3 Triggers of Landslide Dams 26 3.1.4 Types of Landslide 26 3.1.5 Dam Heights and Lake Volumes 32 3.2 Stability, Longevity, and Failure Modes of Landslide Dams 33 3.2.1 Stability of Landslide Dams 33 3.2.2 Longevity of Landslide Dams 35 3.2.3 Failure Modes 36 3.3 Mitigation Measures for Landslide Dams 37 3.3.1 Stages of Landslide Dam Risk Mitigation 38 3.3.2 Engineering Mitigation Measures for Landslide Dams 39 3.3.3 Engineering Measures for the Landslide Dams Induced by the Wenchuan Earthquake 41 3.3.4 Mitigation Measures for the Tangjiashan Landslide Dam 51 4 Statistical Analysis of Failures of Concrete Dams 53 4.1 Database of Failures of Concrete Dams 53 4.2 Failure Modes and Processes 53 4.3 Common Causes of Concrete Dam Failures 55 5 Statistical Analysis of Failures of Dikes 57 5.1 Introduction 57 5.2 Database of Dike Breaching Cases 57 5.3 Evaluation of Dike Failure Mechanisms 59 5.3.1 Most Relevant Failure Mechanisms 59 5.3.2 Statistics of Observed Failure Mechanisms 62 PART II DAM FAILURE MECHANISMS AND BREACHING PROCESS MODELING 67 6 Internal Erosion in Dams and Their Foundations 69 6.1 Concepts of Internal Erosion 69 6.2 Mechanisms of Initiation of Internal Erosion 72 6.2.1 Concentrated Leak Erosion 72 6.2.2 Backward Erosion 73 6.2.3 Contact Erosion 73 6.2.4 Suffusion 74 6.3 Initiation of Concentrated Leak Erosion Through Cracks 74 6.3.1 Causes of Concentrated Leak 75 6.3.2 Need for Studying Soil Erodibility for Concentrated Leak Erosion 80 6.3.3 Laboratory Tests on Concentrated Leak Erosion 81 6.3.4 Factors Affecting Concentrated Leak Erosion 83 6.3.5 Soil Dispersivity 84 6.4 Initiation of Backward Erosion 87 6.4.1 Susceptibility of a Dam or Dike to Backward Erosion 87 6.4.2 Methods for Assessing Backward Erosion 89 6.4.3 Formation of a Pipe due to Backward Erosion 92 6.5 Initiation of Contact Erosion 93 6.5.1 Fundamental Aspects of Contact Erosion Process 94 6.5.2 Laboratory Investigation on Contact Erosion 96 6.5.3 Threshold of Contact Erosion 100 6.6 Initiation of Suffusion 102 6.6.1 Control Parameters for Likelihood of Suffusion 102 6.6.2 Laboratory Testing of Suffusion 103 6.6.3 Geometrical Criteria for Internal Stability of Soils 108 6.6.4 Critical Hydraulic Gradients for Suffusion 115 6.7 Filter Criteria 120 6.7.1 Functions of Filter 120 6.7.2 Filter Criteria 121 6.8 Continuation of Internal Erosion 124 6.9 Progression of Internal Erosion 125 6.10 Suggested Topics for Further Research 126 7 Mechanics of Overtopping Erosion of Dams 127 7.1 Mechanics of Surface Erosion 127 7.1.1 Incipient Motion of Sediment 128 7.1.2 Sediment Transport 133 7.2 Determination of Erodibility of Soils 144 7.2.1 Critical Erosive Shear Stress 144 7.2.2 Coefficient of Erodibility 145 7.2.3 Laboratory Tests 147 7.2.4 Field Tests 151 7.2.5 Classification of Soil Erodibility 155 7.3 Characteristics of Overtopping Erosion Failure of Dams 157 7.3.1 Homogeneous Embankment Dams with Cohesionless Materials 157 7.3.2 Homogeneous Embankment Dams with Cohesive Materials 158 7.3.3 Composite Embankment Dams 159 7.4 Suggested Topics for Further Research 159 8 Dam Breach Modeling 161 8.1 Methods for Dam Breach Modeling 161 8.2 Dam Breaching Data 163 8.2.1 Embankment Dam Breaching Data 163 8.2.2 Landslide Dam Breaching Data 165 8.2.3 Dike Breaching Data 165 8.3 Empirical Analysis Methods 166 8.3.1 Multivariable Regression 166 8.3.2 Empirical Breaching Parameters for Constructed Embankment Dams 169 8.3.3 Empirical Breaching Parameters for Landslide Dams 179 8.3.4 Empirical Breaching Parameters for Dikes 187 8.3.5 Comparison of Breaching Parameters for Landslide Dams and Constructed Embankment Dams 189 8.4 Numerical Simulation of Overtopping Erosion 192 8.4.1 Simplified Physically Based Methods 197 8.4.2 Detailed Physically Based Methods 206 8.4.3 Case Studies 211 8.5 Numerical Simulation of Internal Erosion 215 8.5.1 Continuum Methods 215 8.5.2 Particle Level Analysis 218 8.5.3 Case Studies 218 9 Analysis of Dam Breaching Flood Routing 222 9.1 River Hydraulics 222 9.1.1 One?-dimensional Models 223 9.1.2 Two?-dimensional Models 223 9.2 Numerical Models for Flood Routing Analysis 224 9.2.1 One?-dimensional Numerical Models 224 9.2.2 Two?-dimensional Numerical Models 227 9.2.3 Coupling of 1D/2D Numerical Models 229 9.3 Example - Tangjiashan Landslide Dam Failure 229 9.3.1 Geometric Information 229 9.3.2 Dam Breaching Simulation 232 9.3.3 Boundary and Initial Conditions 232 9.3.4 Flood Routing Analysis and Results 232 PART III DAM FAILURE RISK ASSESSMENT AND MANAGEMENT 241 10 Analysis of Probability of Failure of Dams 243 10.1 Introduction 243 10.2 Analysis Methods 243 10.2.1 Failure Modes and Effects Analysis 243 10.2.2 Event Tree 244 10.2.3 Fault Tree 246 10.2.4 First?-order Reliability Method/First?-order Second?-moment Method 247 10.2.5 Monte Carlo Simulation 250 10.2.6 Bayesian Networks 250 10.3 Examples of Probabilistic Analysis of Dam Failure 253 10.3.1 Probabilistic Analysis of Chinese Dam Distresses 253 10.3.2 Probabilistic Analysis of the Chenbihe Dam Distresses Using Bayesian Networks 264 11 Vulnerability to Dam Breaching Floods 273 11.1 Concepts of Vulnerability 273 11.2 Human Vulnerability to Dam Breaching Floods 273 11.2.1 Human Stability in Flood 274 11.2.2 Influence Factors 277 11.2.3 Methods for Evaluating Human Vulnerability Factor in a Flood 278 11.2.4 Database of Fatalities in Dam/Dike Breaching or Other Floods 283 11.3 Bayesian Network Analysis of Human Vulnerability to Floods 284 11.3.1 Bayesian Networks 284 11.3.2 Building the Bayesian Network for Human Vulnerability 285 11.3.3 Quantifying the Networks 291 11.3.4 Validation of the Model 297 11.4 Damage to Buildings and Infrastructures 300 11.4.1 Flood Action on Buildings 300 11.4.2 Models for Building Damage Evaluation 303 11.4.3 Relationship between Building Damage and Loss of Life 305 11.5 Suggested Topics for Further Research 306 12 Dam Failure Risk Assessment 307 12.1 Risk and Risk Assessment 307 12.1.1 Definition of Risk 307 12.1.2 Risk Management 308 12.2 Dam Failure Risk Analysis 311 12.2.1 Scope Definition 311 12.2.2 Hazards Identification 311 12.2.3 Identification of Failure Modes 312 12.2.4 Estimation of Failure Probability 312 12.2.5 Evaluation of Elements at Risk 313 12.2.6 Vulnerability Evaluation 314 12.2.7 Risk Estimation 314 12.3 Risk Assessment 315 12.3.1 Risk Tolerance Criteria 315 12.3.2 ALARP Considerations 319 12.4 Suggested Topics for Further Research 321 13 Dam Failure Contingency Risk Management 322 13.1 Process of Contingency Risk Management 322 13.1.1 Observation and Prediction 323 13.1.2 Decision?-making 323 13.1.3 Warning 324 13.1.4 Response 325 13.1.5 Evacuation 326 13.2 Decision?-making Under Uncertainty 328 13.2.1 Decision Tree 329 13.2.2 Multi?-phase Decision 330 13.2.3 Influence Diagrams 333 13.3 Dynamic Decision?-Making 334 13.3.1 Dam Failure Emergency Management 336 13.3.2 Dynamic Decision?-making Framework 339 13.3.3 Time Series Models for Estimating Dam Failure Probability 342 13.3.4 Evaluation of the Consequences of Dam Failures 348 13.3.5 Features of DYDEM 350 13.4 Suggested Topics for Further Research 351 14 Case Study: Risk?-based Decision?-making for the Tangjiashan Landslide Dam Failure 353 14.1 Timeline for Decision?-making for the Tangjiashan Landslide Dam Failure 353 14.2 Prediction of Dam Break Probability with Time Series Analysis 355 14.2.1 Forecasting Inflow Rates 355 14.2.2 Forecasting Lake Volume 358 14.2.3 Prediction of Dam Failure Probability 359 14.3 Simulation of Dam Breaching and Flood Routing 361 14.3.1 Simulation of Dam Breaching and Flood Routing in Stage 1 362 14.3.2 Simulation of Dam Breaching and Flood Routing in Stage 2 363 14.3.3 Simulation of Dam Breaching and Flood Routing in Stage 3 365 14.4 Evaluation of Flood Consequences 365 14.4.1 Methodology 366 14.4.2 Calculated Dam Break Flood Consequences 367 14.5 Dynamic Decision?-making 370 14.5.1 Methodology 370 14.5.2 Dynamic Decision?-making in Three Stages 371 14.6 Discussions 374 14.6.1 Influence of the Value of Human Life 374 14.6.2 Influence of Failure Mode 374 14.6.3 Sensitivity of the Minimum Expected Total Consequence 375 PART IV APPENDIXES: DAM FAILURE DATABASES 377 Appendix A: Database of 1443 Cases of Failures of Constructed Dams 379 Appendix B: Database of 1044 Cases of Failures of Landslide Dams 419 References 452 Index 474