1st Edition

Guidelines for Open Pit Slope Design

Edited By John Read, Peter Stacey Copyright 2009
    510 Pages
    by CRC Press

    Guidelines for Open Pit Slope Design is a comprehensive account of the open pit slope design process. Created as an outcome of the Large Open Pit (LOP) project, an international research and technology transfer project on the stability of rock slopes in open pit mines, this book provides an up-to-date compendium of knowledge of the slope design processes that should be followed and the tools that are available to aid slope design practitioners.
    This book links innovative mining geomechanics research into the strength of closely jointed rock masses with the most recent advances in numerical modelling, creating more effective ways for predicting the reliability of rock slopes in open pit mines. It sets out the key elements of slope design, the required levels of effort and the acceptance criteria that are needed to satisfy best practice with respect to pit slope investigation, design, implementation and performance monitoring.
    This book will assist open pit mine slope design practitioners, including engineering geologists, geotechnical engineers, mining engineers and civil engineers and mine managers, in meeting stakeholder requirements for pit slopes that are stable, in regards to safety, ore recovery and financial return, for the required life of the mine.

    Preface and acknowledgments

    1 Fundamentals of slope design
    Peter Stacey
    1.1 Introduction
    1.2 Pit slope designs
    1.2.1 Safety/social factors
    1.2.2 Economic factors
    1.2.3 Environmental and regulatory factors
    1.3 Terminology of slope design
    1.3.1 Slope configurations
    1.3.2 Instability
    1.3.3 Rockfall
    1.4 Formulation of slope designs
    1.4.1 Introduction
    1.4.2 Geotechnical model (Chapter 7)
    1.4.3 Data uncertainty (Chapter 8)
    1.4.4 Acceptance criteria (Chapter 9)
    1.4.5 Slope design methods (Chapter 10)
    1.4.6 Design implementation (Chapter 11)
    1.4.7 Slope evaluation and monitoring (Chapter 12)
    1.4.8 Risk management (Chapter 13)
    1.4.9 Closure (Chapter 14)
    1.5 Design requirements by project level
    1.5.1 Project development
    1.5.2 Study requirements
    1.6 Review
    1.6.1 Overview
    1.6.2 Review levels
    1.6.3 Geotechnically competent person
    1.7 Conclusion

    2 Field data collection
    John Read, Jarek Jakubec and Geoff Beale
    2.1 Introduction
    2.2 Outcrop mapping and logging
    2.2.1 Introduction
    2.2.2 General geotechnical logging
    2.2.3 Mapping for structural analyses
    2.2.4 Surface geophysical techniques
    2.3 Overburden soils logging
    2.3.1 Classification
    2.3.2 Strength and relative density
    2.4 Core drilling and logging
    2.4.1 Introduction
    2.4.2 Planning and scoping
    2.4.3 Drill hole location and collar surveying
    2.4.4 Core barrels
    2.4.5 Downhole surveying
    2.4.6 Core orientation
    2.4.7 Core handling and documentation
    2.4.8 Core sampling, storage and preservation
    2.4.9 Core logging
    2.4.10 Downhole geophysical techniques
    2.5 Groundwater data collection
    2.5.1 Approach to groundwater data collection
    2.5.2 Tests conducted during RC drilling
    2.5.3 Piezometer installation
    2.5.4 Guidance notes: installation of test wells for pit slope depressurisation
    2.5.5 Hydraulic tests
    2.5.6 Setting up pilot depressurisation trials
    2.6 Data management

    3 Geological model
    John Read and Luke Keeney
    3.1 Introduction
    3.2 Physical setting
    3.3 Ore body environments
    3.3.1 Introduction
    3.3.2 Porphyry deposits
    3.3.3 Epithermal deposits
    3.3.4 Kimberlites
    3.3.5 VMS deposits
    3.3.6 Skarn deposits
    3.3.7 Stratabound deposits
    3.4 Geotechnical requirements
    3.5 Regional seismicity
    3.5.1 Distribution of earthquakes
    3.5.2 Seismic risk
    3.6 Regional stress

    4 Structural model
    John Read
    4.1 Introduction
    4.2 Model components
    4.2.1 Major structures
    4.2.2 Fabric
    4.3 Geological environments
    4.3.1 Introduction
    4.3.2 Intrusive
    4.3.3 Sedimentary
    4.3.4 Metamorphic
    4.4 Structural modelling tools
    4.4.1 Solid modelling
    4.4.2 Stereographic projection
    4.4.3 Discrete fracture network modelling
    4.5 Structural domain definition
    4.5.1 General guidelines
    4.5.2 Example application

    5 Rock mass model
    Antonio Karzulovic and John Read
    5.1 Introduction
    5.2 Intact rock strength
    5.2.1 Introduction
    5.2.2 Index properties
    5.2.3 Mechanical properties
    5.2.4 Special conditions
    5.3 Strength of structural defects
    5.3.1 Terminology and classification
    5.3.2 Defect strength
    5.4 Rock mass classification
    5.4.1 Introduction
    5.4.2 RMR, Bieniawski
    5.4.3 Laubscher IRMR and MRMR
    5.4.4 Hoek-Brown GSI
    5.5 Rock mass strength
    5.5.1 Introduction
    5.5.2 Laubscher strength criteria
    5.5.3 Hoek-Brown strength criterion
    5.5.5 Directional rock mass strength
    5.5.6 Synthetic rock mass model

    6 Hydrogeological model
    Geoff Beale
    6.1 Hydrogeology and slope engineering
    6.1.1 Introduction
    6.1.2 Porosity and pore pressure
    6.1.3 General mine dewatering and localised pore pressure control
    6.1.4 Making the decision to depressurise
    6.1.5 Developing a slope depressurisation program
    6.2 Background to groundwater hydraulics
    6.2.1 Groundwater flow
    6.2.2 Porous-medium (intergranular) groundwater settings
    6.2.3 Fracture-flow groundwater settings
    6.2.4 Influences on fracturing and groundwater
    6.2.5 Mechanisms controlling pore pressure reduction
    6.3 Developing a conceptual hydrogeological model of pit slopes
    6.3.1 Integrating the pit slope model into the regional model
    6.3.2 Conceptual mine scale hydrogeological model
    6.3.3 Detailed hydrogeological model of pit slopes
    6.4 Numerical hydrogeological models
    6.4.1 Introduction
    6.4.2 Numerical hydrogeological models for mine scale dewatering applications
    6.4.3 Pit slope scale numerical modelling
    6.4.4 Numerical modelling for pit slope pore pressures
    6.4.5 Coupling pore pressure and geotechnical models
    6.5 Implementing a slope depressurisation program
    6.5.1 General mine dewatering
    6.5.2 Specific programs for control of pit slope pressures
    6.5.3 Selecting a slope depressurisation method
    6.5.4 Use of blasting to open up drainage pathways
    6.5.5 Water management and control
    6.6 Areas for future research
    6.6.1 Introduction
    6.6.2 Relative pore pressure behaviour between high-order and low-order fractures
    6.6.3 Standardising the interaction between pore pressure and geotechnical models
    6.6.4 Investigation of transient pore pressures
    6.6.5 Coupled pore pressure and geotechnical modelling

    7 Geotechnical model
    Alan Guest and John Read
    7.1 Introduction
    7.2 Constructing the geotechnical model
    7.2.1 Required output
    7.2.2 Model development
    7.2.3 Building the model
    7.2.4 Block modelling approach
    7.3 Applying the geotechnical model
    7.3.1 Scale effects
    7.3.2 Classification systems
    7.3.3 Hoek-Brown rock mass strength criterion
    7.3.4 Pore pressure considerations

    8 Data uncertainty
    John Read
    8.1 Introduction
    8.2 Causes of data uncertainty
    8.3 Impact of data uncertainty
    8.4 Quantifying data uncertainty
    8.4.1 Overview
    8.4.2 Subjective assessment
    8.4.3 Relative frequency concepts
    8.5 Reporting data uncertainty
    8.5.1 Geotechnical reporting system
    8.5.2 Assessment criteria checklist
    8.6 Summary and conclusions

    9 Acceptance criteria
    Johan Wesseloo and John Read
    9.1 Introduction
    9.2 Factor of safety
    9.2.1 FoS as a design criterion
    9.2.2 Tolerable factors of safety
    9.3 Probability of failure
    9.3.1 PoF as a design criterion
    9.3.2 Acceptable levels of PoF
    9.4 Risk model
    9.4.1 Introduction
    9.4.2 Cost–benefit analysis
    9.4.3 Risk model process
    9.4.4 Formulating acceptance criteria
    9.4.5 Slope angles and levels of confidence
    9.5 Summary

    10 Slope design methods
    Loren Lorig, Peter Stacey and John Read
    10.1 Introduction
    10.1.1 Design steps
    10.1.2 Design analyses
    10.2 Kinematic analyses
    10.2.1 Benches
    10.2.2 Inter-ramp slopes
    10.3 Rock mass analyses
    10.3.1 Overview
    10.3.2 Empirical methods
    10.3.3 Limit equilibrium methods
    10.3.4 Numerical methods
    10.3.5 Summary recommendations

    11 Design implementation
    Peter Williams, John Floyd, Gideon Chitombo and Trevor Maton
    11.1 Introduction
    11.2 Mine planning aspects of slope design
    11.2.1 Introduction
    11.2.2 Open pit design philosophy
    11.2.3 Open pit design process
    11.2.4 Application of slope design criteria in mine design
    11.2.5 Summary and conclusions
    11.3 Controlled blasting
    11.3.1 Introduction
    11.3.2 Design terminology
    11.3.3 Blast damage mechanisms
    11.3.4 Influence of geology on blast-induced damage
    11.3.5 Controlled blasting techniques
    11.3.6 Delay configuration
    11.3.7 Design implementation
    11.3.8 Performance monitoring and analysis Post blast inspection Post excavation inspection and batter quantification
    11.3.9 Design refinement
    11.3.10 Design platform
    11.3.11 Planning and optimisation cycle
    11.4 Excavation and scaling
    11.4.1 Excavation
    11.4.2 Scaling and bench cleanup
    11.4.3 Evaluation of bench design achievement
    11.5 Artificial support
    11.5.1 Basic approaches
    11.5.2 Stabilisation, repair and support methods
    11.5.3 Design considerations
    11.5.4 Economic considerations
    11.5.5 Safety considerations
    11.5.6 Specific situations
    11.5.7 Reinforcement measures
    11.5.8 Rockfall protection measures

    12 Performance assessment and monitoring
    Mark Hawley, Scott Marisett, Geoff Beale and Peter Stacey
    12.1 Assessing slope performance
    12.1.2 Geotechnical model validation and refinement
    12.1.3 Bench performance
    12.1.4 Inter-ramp slope performance
    12.1.5 Overall slope performance
    12.1.6 Summary and conclusions
    12.2 Slope monitoring
    12.2.1 Introduction
    12.2.2 Movement monitoring systems
    12.2.3 Guidelines on the execution of monitoring programs
    12.3 Ground control management plans
    12.3.1 Introduction
    12.3.2 Slope stability plan

    13 Risk management
    Ted Brown and Alison Booth
    13.1 Introduction
    13.1.1 Background
    13.1.2 Purpose and content of this chapter
    13.1.3 Sources of Information
    13.2 Overview of risk management
    13.2.1 Definitions
    13.2.2 General risk management process
    13.2.3 Risk management in the minerals industry
    13.3 Geotechnical risk management for open pit slopes
    13.4 Risk assessment methodologies
    13.4.1 Approaches to risk assessment
    13.4.2 Risk identification
    13.4.3 Risk analysis
    13.4.4 Risk evaluation
    13.5 Risk mitigation
    13.5.1 Overview
    13.5.2 Hierarchy of controls
    13.5.3 Geotechnical control measures
    13.5.4 Mitigation plans
    13.5.5 Monitoring, review and feedback

    14 Open pit closure
    Dirk van Zyl
    14.1 Introduction
    14.2 Mine closure planning for open pits
    14.2.1 Introduction
    14.2.2 Closure planning for new mines
    14.2.3 Closure planning for existing mines
    14.2.4 Risk assessment and management
    14.3 Open pit closure planning
    14.3.1 Closure goals and criteria
    14.3.2 Site characterisation
    14.3.3 Ore body characteristics and mining approach
    14.3.4 Surface water diversion
    14.3.5 Pit water balance
    14.3.6 Pit lake water quality
    14.3.7 Ecological risk assessment
    14.3.8 Pit wall stability
    14.3.9 Pit access
    14.3.10 Reality of open pit closure
    14.4 Open pit closure activities and post-closure monitoring
    14.4.1 Closure activities
    14.4.2 Post-closure monitoring
    14.5 Conclusions


    Appendix 1: Groundwater data collection
    Appendix 2: Essential statistical and probability theory
    Appendix 3: Influence of in situ stresses on open pit design
    Appendix 4: Risk management: geotechnical hazard checklists
    Appendix 5: Example regulations for open pit closure

    Terminology and definitions






    Dr. Read has over 40 years experience as a practitioner and consultant in the mining industry, with special interests and expertise in rock slope stability. In 1990 Dr Read began his own geotechnical engineering practice. Since then he has specialised in slope stability and open pit mine slope design and investigation tasks in Australia, Fiji, Papua New Guinea, Brazil, Argentina, Chile, Canada, South Africa, and Zambia. From 1994 to 2004 he was Deputy Chief of CSIRO Exploration & Mining and Executive Manager of the Queensland Centre for Advanced Technologies, Brisbane.

    Peter Stacey has accumulated over 45 years of international experience in the geotechnical aspects of open pits, including slope design and implementation, as well as project management. He holds a B.Sc. Hons. degree in Geology, a D.I.C. from Imperial College, London, and is a registered engineer in Canada and the UK. After working for the Geological Survey of Sweden and subsequently with the Iron Ore Company of Canada as Supervisor – Geotechnical Engineering, Mr Stacey joined Golder Associates Ltd., based in Vancouver, Canada. During his 29 years with Golder, Mr Stacey worked primarily in the areas of pit slope design and the application of geotechnical engineering to the operational aspects of open pit mines around the world.
    In 2003, Mr Stacey formed Stacey Mining Geotechnical Ltd. to concentrate on independent review consulting. In this capacity, he is currently engaged in performing geotechnical reviews for a number of international mining and consulting companies, and is a member of Geotechnical Review Boards for several large open pit operations. In addition, he leads courses in pit slope design and implementation.