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GUIDELINES FOR
OPEN PIT SLOPE DESIGN
EDITORS: JOHN READ, PETER STACEY
# &CSIRO J
PUBLISHING x S
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Contents
Preface and acknowledgments xiii
1 Fundamentals of slope design 1
Peter Stacey
1.1 Introduction 1
1.2 Pit slope designs 1
1.2.1 Safety/social factors 2
1.2.2 Economic factors 2
1.2.3 Environmental and regulatory factors 3
1.3 Terminology of slope design 4
1.3.1 Slope configurations 4
1.3.2 Instability 4
1.3.3 Rockfall 6
1.4 Formulation of slope designs 6
1.4.1 Introduction 6
1.4.2 Geotechnical model 6
1.4.3 Data uncertainty (Chapter 8) 8
1.4.4 Acceptance criteria (Chapter 9 ) 8
1.4.5 Slope design methods (Chapter 10) 9
1.4.6 Design implementation (Chapter 11) 10
1.4.7 Slope evaluation and monitoring (Chapter 12) 10
1.4.8 Risk management (Chapter 13) 11
1.4.9 Closure (Chapter 1 4) 11
1.5 Design requirements by project level 11
1.5.1 Project development 111.5.2 Study requirements 12
1.6 Review 12
1.6.1 Overview 12
1.6.2 Review levels 14
1.6.3 Geotechnically competent person 14
1.7 Conclusion 14
2 Field data collection 15
John Read, Jarek Jakubec and GeoffBeale
2.1 Introduction 15
2.2 Outcrop mapping and logging 15
2.2.1 Introduction 15
2.2.2 General geotechnical logging 17
2.2.3 Mapping for structural analyses 19
2.2.4 Surface geophysical techniques 22
2.3 Overburden soils logging 23
2.3.1 Classification 23
2.3.2 Strength and relative density 26
2.4 Core drilling and logging 26
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vi Guidelines for Open Pit Slope Design
2.4.1 Introduction 26
2.4.2 Planning and scoping 26
2.4.3 Drill hole location and collar surveying 27
2.4.4 Core barrels 27
2.4.5 Downhole surveying 27
2.4.6 Core orientation 28
2.4.7 Core handling and documentation 29
2.4.8 Core sampling, storage and preservation 31
2.4.9 Core logging 32
2.4.10 Downhole geophysical techniques 39
2.5 Groundwater data collection 40
2.5.1 Approach to groundwater data collection 40
2.5.2 Tests conducted during RC drilling 42
2.5.3 Piezometer installation 44
2.5.4 Guidance notes: installation of test wells for pit slope
depressurisation 47
2.5.5 Hydraulic tests 49
2.5.6 Setting up pilot depressurisation trials 51
2.6 Data management 52
Endnotes 52
3 Geological model 53
John Read and Luke Keeney
3.1 Introduction 53
3.2 Physical setting 53
3.3 Ore body environments 55
3.3.1 Introduction 55
3.3.2 Porphyry deposits 55
3.3.3 Epithermal deposits 56
3.3.4 Kimberlites 56
3.3.5 VMS deposits 57
3.3.6 Skarn deposits 57
3.3.7 Stratabound deposits 57
3.4 Geotechnical requirements 59
3.5 Regional seismicity 62
3.5.1 Distribution of earthquakes 62
3.5.2 Seismic risk data 65
3.6 Regional stress 66
4 Structural model 69
John Read
4.1 Introduction 69
4.2 Model components 69
4.2.1 Major structures 69
4.2.2 Fabric 75
4.3 Geological environments 764.3.1 Introduction 76
4.3.2 Intrusive 76
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Contents vii
4.3.3 Sedimentary 76
4.3.4 Metamorphic 77
4.4 Structural modelling tools 77
4.4.1 Solid modelling 77
4.4.2 Stereographic projection 774.4.3 Discrete fracture network modelling 79
4.5 Structural domain definition 80
4.5.1 General guidelines 804.5.2 Example application 80
5 Rock mass model 83
Antonio Karzulovic and John Read
5.1 Introduction 83
5.2 Intact rock strength 83
5.2.1 Introduction 83
5.2.2 Index properties 85
5.2.3 Mechanical properties 88
5.2.4 Special conditions 92
5.3 Strength of structural defects 94
5.3.1 Terminology and classification 94
5.3.2 Defect strength 94
5.4 Rock mass classification 117
5.4.1 Introduction 117
5.4.2 RMR, Bieniawski 117
5.4.3 Laubscher IRMR and MRMR 119
5.4.4 Hoek-Brown GSI 123
5.5 Rock mass strength 127
5.5.1 Introduction 127
5.5.2 Laubscher strength criteria 127
5.5.3 Hoek-Brown strength criterion 128
5.5.4 CNI criterion 130
5.5.5 Directional rock mass strength 132
5.5.6 Synthetic rock mass model 138
6 Hydrogeological model 141GeoffBeak
6.1 Hydrogeology and slope engineering 141
6.1.1 Introduction 141
6.1.2 Porosity and pore pressure 141
6.1.3 General mine
dewatering and localised pore pressure control 1466.1.4 Making the decision to depressurise 148
6.1.5 Developing a slope depressurisation program 151
6.2 Background to groundwater hydraulics 151
6.2.1 Groundwater flow 151
6.2.2 Porous-medium (intergranular) groundwater settings 154
6.2.3 Fracture-flow groundwater settings 156
6.2.4 Influences on fracturing and groundwater 161
6.2.5 Mechanisms controlling pore pressure reduction 163
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viii Guidelines for Open Pit Slope Design
6.3 Developing a conceptual hydrogeological model of pit slopes 166
6.3.1 Integrating the pit slope model into the regional model 166
6.3.2 Conceptual mine scale hydrogeological model 166
6.3.3 Detailed hydrogeological model of pit slopes 167
6.4 Numerical hydrogeological models 168
6.4.1 Introduction 168
6.4.2 Numerical hydrogeological models for mine scale dewateringapplications 169
6.4.3 Pit slope scale numerical modelling 173
6.4.4 Numerical modelling for pit slope pore pressures 175
6.4.5 Coupling pore pressure and geotechnical models 179
6.5 Implementing a slope depressurisation program 180
6.5.1 General mine dewatering 180
6.5.2 Specific programs for control of pit slope pressures 181
6.5.3 Selecting a slope depressurisation method 192
6.5.4 Use of blasting to open up drainage pathways 192
6.5.5 Water management and control 192
6.6 Areas for future research 195
6.6.1 Introduction 195
6.6.2 Relative pore pressure behaviour between high-order and low-
order fractures 195
6.6.3 Standardising the interaction between pore pressure and
geotechnical models 196
6.6.4 Investigation of transient pore pressures 197
6.6.5 Coupled pore pressure and geotechnical modelling 197
7 Geotechnical model 201
Alan Guest and John Read
7.1 Introduction 201
7.2 Constructing the geotechnical model 2017.2.1 Required output 201
7.2.2 Model development 202
7.2.3 Building the model 202
7.2.4 Block modelling approach 205
7.3 Applying the geotechnical model 206
7.3.1 Scale effects 206
7.3.2 Classification systems 210
7.3.3 Hoek-Brown rock mass strength criterion 210
7.3.4 Pore pressure considerations 211
8 Data
uncertainty 213
John Read
8.1 Introduction 213
8.2 Causes of data uncertainty 213
8.3 Impact of data uncertainty 213
8.4 Quantifying data uncertainty 215
8.4.1 Overview 215
8.4.2 Subjective assessment 215
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Contents
8.4.3 Relative frequency concepts 216
8.5 Reporting data uncertainty 216
8.5.1 Geotechnical reporting system 216
8.5.2 Assessment criteria checklist 219
8.6 Summary and conclusions 219
9 Acceptance criteria 221
]ohan Wesseloo and John Read
9.1 Introduction 221
9.2 Factor of safety 221
9.2.1 FoS as a design criterion 221
9.2.2 Tolerable factors of safety 223
9.3 Probability of failure 223
9.3.1 PoF as a design criterion 223
9.3.2 Acceptable levels of PoF 224
9.4 Risk model 225
9.4.1 Introduction 225
9.4.2 Cost-benefit analysis 226
9.4.3 Risk model process 228
9.4.4 Formulating acceptance criteria 232
9.4.5 Slope angles and levels of confidence 234
9.5 Summary 235
10 Slope design methods 237Loren Lorig, Peter Stacey and John Read
10.1 Introduction 237
10.1.1 Design steps 237
10.1.2 Design analyses 238
10.2 Kinematic analyses 239
10.2.1 Benches 239
10.2.2 Inter-ramp slopes 244
10.3 Rock mass analyses 246
10.3.1 Overview 246
10.3.2 Empirical methods 246
10.3.3 Limit equilibrium methods 248
10.3.4 Numerical methods 253
10.3.5 Summary recommendations 263
11 Design implementation 265
Peter Williams, John Floyd, Gideon Chitombo and Trevor Maton
11.1 Introduction 265
11.2 Mine planning aspects of slope design 26511.2.1 Introduction 265
11.2.2 Open pi t design philosophy 265
11.2.3 Open pit design process 267
11.2.4 Application of slope design criteria in mine design 268
11.2.5 Summary and conclusions 276
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X Guidelines for Open Pit Slope Design
11.3 Controlled blasting 276
11.3.1 Introduction 276
11.3.2 Design terminology 277
11.3.3 Blast damage mechanisms 278
11.3.4 Influence of geology on blast-induced damage 279
11.3.5 Controlled blasting techniques 282
11.3.6 Delay configuration 292
11.3.7 Design implementation 294
11.3.8 Performance monitoring and analysis 296
11.3.9 Design refinement 299
11.3.10 Design platform 305
11.3.11 Planning and optimisation cycle 306
11.4 Excavation and scaling 310
11.4.1 Excavation 310
11.4.2 Scaling and bench cleanup 312
11.4.3 Evaluation of bench design achievement 313
11.5 Artificial support 313
11.5.1 Basic approaches 313
11.5.2 Stabilisation, repair and support methods 31411.5.3 Design considerations 315
11.5.4 Economic considerations 316
11.5.5 Safety considerations 317
11.5.6 Specific situations 317
11.5.7 Reinforcement measures 318
11.5.8 Rockfall protection measures 325
12 Performance assessment and monitoring 327Mark Hawley, Scott Marisett, Geoff Beale and Peter Stacey
12.1 Assessing slope performance 327
12.1.1 Introduction 327
12.1.2 Geotechnical model validation and refinement 327
12.1.3 Bench performance 329
12.1.4 Inter-ramp slope performance 337
12.1.5 Overall slope performance 339
12.1.6 Summary and conclusions 342
12.2 Slope monitoring 342
12.2.1 Introduction 342
12.2.2 Movement monitoring systems 343
12.2.3 Guidelines on the execution of monitoring programs 363
12.3 Ground control management plans 370
12.3.1 Introduction 370
12.3.2 Hazard management plan 371
13 Risk management 381
Ted Brown and Alison Booth
13.1 Introduction 381
13.1.1 Background 381
13.1.2 Purpose and content of this chapter 381
13.1.3 Sources of information 382
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Contents : xi
13.2 Overview of risk management 383
13.2.1 Definitions 383
13.2.2 General risk management process 383
13.2.3 Risk management in the minerals industry 384
13.3 Geotechnical risk management for open pit slopes 385
13.4 Risk assessment methodologies 389
13.4.1 Approaches to risk assessment 389
13.4.2 Risk identification 389
13.4.3 Risk analysis 391
13.4.4 Risk evaluation 395
13.5 Risk mitigation 396
13.5.1 Overview 396
13.5.2 Hierarchy of controls 398
13.5.3 Geotechnical control measures 398
13.5.4 Mitigation plans 399
13.5.5 Monitoring, review and feedback 400
14 Open pit closure 401Dirk van Zyl
14.1 Introduction 401
14.2 Mine closure planning for open pits 403
14.2.1 Introduction 403
14.2.2 Closure planning for new mines 403
14.2.3 Closure planning for existing mines 403
14.2.4 Risk assessment and management 405
14.3 Open pit closure planning 405
14.3.1 Closure goals and criteria 405
14.3.2 Site characterisation 407
14.3.3 Ore body characteristics and mining approach 408
14.3.4 Surface water diversion 409
14.3.5 Pit water balance 409
14.3.6 Pit lake water quality 409
14.3.7 Ecological risk assessment 410
14.3.8 Pit wall stability 410
14.3.9 Pit access 412
14.3.10 Reality of open pit closure 412
14.4 Open pit closure activities and post-closure monitoring 412
14.4.1 Closure activities 412
14.4.2 Post-closure monitoring 412
14.5 Conclusions 412
Endnotes 413
Appendix 1 415
Groundwater data collection
Appendix 2 431
Essential statistical and probability theory
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xii Guidelines for Open Pit Slope Design
Appendix 3 437
Influence of in situ stresses on open pit design
EvertHoek, Jean Hutchinson, Kathy Kalenchuk and Mark Diederichs
App end ix 4 447
Risk management: geotechnical hazard checklists
App end ix 5 459
Example regulations for open pit closure
Terminology and definitions 462
References 467
Index 487
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