GUIDELINES FOR OPEN PIT SLOPE DESIGN EDITORS: JOHN READ, PETER STACEY # & CSIRO. J x PUBLISHING

Transcription

1 GUIDELINES FOR OPEN PIT SLOPE DESIGN EDITORS: JOHN READ, PETER STACEY # & CSIRO J x PUBLISHING S

2 Contents Preface and acknowledgments xiii 1 Fundamentals of slope design 1 Peter Stacey 1.1 Introduction Pit slope designs Safety/social factors Economic factors Environmental and regulatory factors Terminology of slope design Slope configurations Instability Rockfall Formulation of slope designs Introduction Geotechnical model Data uncertainty (Chapter 8) Acceptance criteria (Chapter 9) Slope design methods (Chapter 10) Design implementation (Chapter 11) Slope evaluation and monitoring (Chapter 12) Risk management (Chapter 13) Closure (Chapter 14) Design requirements by project level Project development Study requirements Review Overview Review levels Geotechnically competent person Conclusion 14 2 Field data collection 15 John Read, Jarek Jakubec and GeoffBeale 2.1 Introduction Outcrop mapping and logging Introduction General geotechnical logging Mapping for structural analyses Surface geophysical techniques Overburden soils logging Classification Strength and relative density Core drilling and logging 26

3 vi Guidelines for Open Pit Slope Design Introduction Planning and scoping Drill hole location and collar surveying Core barrels Downhole surveying Core orientation Core handling and documentation Core sampling, storage and preservation Core logging Downhole geophysical techniques Groundwater data collection Approach to groundwater data collection Tests conducted during RC drilling Piezometer installation Guidance notes: installation of test wells for pit slope depressurisation Hydraulic tests Setting up pilot depressurisation trials Data management 52 Endnotes 52 3 Geological model 53 John Read and Luke Keeney 3.1 Introduction Physical setting Ore body environments Introduction Porphyry deposits Epithermal deposits Kimberlites VMS deposits Skarn deposits Stratabound deposits Geotechnical requirements Regional seismicity Distribution of earthquakes Seismic risk data Regional stress 66 4 Structural model 69 John Read 4.1 Introduction Model components Major structures Fabric Geological environments Introduction Intrusive 76

4 Contents vii Sedimentary Metamorphic Structural modelling tools Solid modelling Stereographic projection Discrete fracture network modelling Structural domain definition General guidelines Example application 80 5 Rock mass model 83 Antonio Karzulovic and John Read 5.1 Introduction Intact rock strength Introduction Index properties Mechanical properties Special conditions Strength of structural defects Terminology and classification Defect strength Rock mass classification Introduction RMR, Bieniawski Laubscher IRMR and MRMR Hoek-Brown GSI Rock mass strength Introduction Laubscher strength criteria Hoek-Brown strength criterion CNI criterion Directional rock mass strength Synthetic rock mass model Hydrogeological Geoff Beak model Hydrogeology and slope engineering Introduction Porosity and pore pressure General mine dewatering and localised pore pressure control Making the decision to depressurise Developing a slope depressurisation program Background to groundwater hydraulics Groundwater flow Porous-medium (intergranular) groundwater settings Fracture-flow groundwater settings Influences on fracturing and groundwater Mechanisms controlling pore pressure reduction 163

5 viii Guidelines for Open Pit Slope Design 6.3 Developing a conceptual hydrogeological model of pit slopes Integrating the pit slope model into the regional model Conceptual mine scale hydrogeological model Detailed hydrogeological model of pit slopes Numerical hydrogeological models Introduction Numerical hydrogeological models for mine scale dewatering applications Pit slope scale numerical modelling Numerical modelling for pit slope pore pressures Coupling pore pressure and geotechnical models Implementing a slope depressurisation program General mine dewatering Specific programs for control of pit slope pressures Selecting a slope depressurisation method Use of blasting to open up drainage pathways Water management and control Areas for future research Introduction Relative pore pressure behaviour between high-order and loworder fractures Standardising the interaction between pore pressure and geotechnical 181 models Investigation of transient pore pressures Coupled pore pressure and geotechnical modelling Geotechnical model 201 Alan Guest and John Read 7.1 Introduction Constructing the geotechnical model Required output Model development Building the model Block modelling approach Applying the geotechnical model Scale effects Classification systems Hoek-Brown rock mass strength criterion Pore pressure considerations Data uncertainty 213 John Read 8.1 Introduction Causes of data uncertainty Impact of data uncertainty Quantifying data uncertainty Overview Subjective assessment 215

6 Contents Relative frequency concepts Reporting data uncertainty Geotechnical reporting system Assessment criteria checklist Summary and conclusions Acceptance criteria 221 ]ohan Wesseloo and John Read 9.1 Introduction Factor of safety FoS as a design criterion Tolerable factors of safety Probability of failure PoF as a design criterion Acceptable levels of PoF Risk model Introduction Cost-benefit analysis Risk model process Formulating acceptance criteria Slope angles and levels of confidence Summary Slope design methods 237 Loren Lorig, Peter Stacey and John Read 10.1 Introduction Design steps Design analyses Kinematic analyses Benches Inter-ramp slopes Rock mass analyses Overview Empirical methods Limit equilibrium methods Numerical methods Summary recommendations Design implementation 265 Peter Williams, John Floyd, Gideon Chitombo and Trevor Maton 11.1 Introduction Mine planning aspects of slope design Introduction Open pit design philosophy Open pit design process Application of slope design criteria in mine design Summary and conclusions 276

7 X Guidelines for Open Pit Slope Design 11.3 Controlled blasting Introduction Design terminology Blast damage mechanisms Influence of geology on blast-induced damage Controlled blasting techniques Delay configuration Design implementation Performance monitoring and analysis Design refinement Design platform Planning and optimisation cycle Excavation and scaling Excavation Scaling and bench cleanup Evaluation of bench design achievement Artificial support Basic approaches Stabilisation, repair and support methods Design considerations Economic considerations Safety considerations Specific situations Reinforcement measures Rockfall protection measures Performance assessment and monitoring 327 Mark Hawley, Scott Marisett, Geoff Beale and Peter Stacey 12.1 Assessing slope performance Introduction Geotechnical model validation and refinement Bench performance Inter-ramp slope performance Overall slope performance Summary and conclusions Slope monitoring Introduction Movement monitoring systems Guidelines on the execution of monitoring programs Ground control management plans Introduction Hazard management plan Risk management 381 Ted Brown and Alison Booth 13.1 Introduction Background Purpose and content of this chapter Sources of information 382

8 Contents : xi 13.2 Overview of risk management Definitions General risk management process Risk management in the minerals industry Geotechnical risk management for open pit slopes Risk assessment methodologies Approaches to risk assessment Risk identification Risk analysis Risk evaluation Risk mitigation Overview Hierarchy of controls Geotechnical control measures Mitigation plans Monitoring, review and feedback Open pit closure 401 Dirk van Zyl 14.1 Introduction Mine closure planning for open pits Introduction Closure planning for new mines Closure planning for existing mines Risk assessment and management Open pit closure planning Closure goals and criteria Site characterisation Ore body characteristics and mining approach Surface water diversion Pit water balance Pit lake water quality Ecological risk assessment Pit wall stability Pit access Reality of open pit closure Open pit closure activities and post-closure monitoring Closure activities Post-closure monitoring Conclusions 412 Endnotes 413 Appendix Groundwater data collection Appendix Essential statistical and probability theory

9 xii Guidelines for Open Pit Slope Design Appendix Influence of in situ stresses on open pit design EvertHoek, Jean Hutchinson, Kathy Kalenchuk and Mark Diederichs Appendix Risk management: geotechnical hazard checklists Appendix Example regulations for open pit closure Terminology and definitions 462 References 467 Index 487