1st Edition

Guidelines for Open Pit Slope Design in Weak Rocks

Edited By Derek Martin, Peter Stacey Copyright 2018
    414 Pages 580 Color Illustrations
    by CRC Press

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    Weak rocks encountered in open pit mines cover a wide variety of materials, with properties ranging between soil and rock. As such, they can provide a significant challenge for the slope designer. For these materials, the mass strength can be the primary control in the design of the pit slopes, although structures can also play an important role. Because of the typically weak nature of the materials, groundwater and surface water can also have a controlling influence on stability.

    Guidelines for Open Pit Slope Design in Weak Rocks is a companion to Guidelines for Open Pit Slope Design, which was published in 2009 and dealt primarily with strong rocks. Both books were commissioned under the Large Open Pit (LOP) project, which is sponsored by major mining companies. These books provide summaries of the current state of practice for the design, implementation and assessment of slopes in open pits, with a view to meeting the requirements of safety, as well as the recovery of anticipated ore reserves.

    This book, which follows the general cycle of the slope design process for open pits, contains 12 chapters. These chapters were compiled and written by industry experts and contain a large number of case histories. The initial chapters address field data collection, the critical aspects of determining the strength of weak rocks, the role of groundwater in weak rock slope stability and slope design considerations, which can differ somewhat from those applied to strong rock. The subsequent chapters address the principal weak rock types that are encountered in open pit mines, including cemented colluvial sediments, weak sedimentary mudstone rocks, soft coals and chalk, weak limestone, saprolite, soft iron ores and other leached rocks, and hydrothermally altered rocks. A final chapter deals with design implementation aspects, including mine planning, design implementation, monitoring, surface water control and closure of weak rock slopes.

    Key Features:

    • Illustration of the best practice in modern open pit mines
    • State of the art approaches for challenging designs
    • Use of numerous case histories written by large-open pit operators to illustrate state of practice
    • Individual chapters/sections written by leaders in the industry

    As with the other books in this series, Guidelines for Open Pit Slope Design in Weak Rocks provides guidance to practitioners involved in the design and implementation of open pit slopes, particularly geotechnical engineers, mining engineers, geologists and other personnel working at operating mines.

    1 Introduction
    Peter Stacey and Derek Martin
    1.1 Background
    1.2 General descriptions and definitions for weak rocks
    1.3 Slope design terminology
    1.4 Design implications
    1.5 Design implementation

    2 Field data collection and methodology
    Peter Stacey and Derek Martin
    2.1 Introduction
    2.2 General field descriptions
    2.3 Field mapping
    2.4 Core logging, sampling and sample preservation
    2.5 Laboratory testing
    2.6 In-situ borehole characterisation
    2.7 Summary

    3 Weak rock strength models
    Derek Martin and Peter Stacey
    3.1 Introduction
    3.2 Geological and structural models
    3.3 Role of rock mass classifications systems
    3.4 Shear strength and failure criteria of weak rocks in laboratory tests
    3.5 Erodibility/degradability

    4 The role of water in slope design for weak rocks
    Geoff Beale
    4.1 Introduction
    4.2 Hydrogeological background
    4.3 Groundwater characterisation
    4.4 Development of a conceptual hydrogeological model
    4.5 Analysis and modelling of pore pressure
    4.6 Depressurisation of weak rocks
    4.7 Characterisation of surface water

    5 Slope design considerations
    Derek Martin, Loren Lorig and Peter Stacey
    5.1 Introduction
    5.2 Modes of failure
    5.3 Instability mechanisms
    5.4 Stability analyses and predictions
    5.5 Limit equilibrium analyses
    5.6 Numerical approaches
    5.7 Role of back analyses
    5.8 Acceptance criteria
    5.9 Summary

    6 Cemented sediments
    Derek Martin and Pete Stacey
    6.1 Introduction
    6.2 General geological setting
    6.3 Hydrogeology
    6.4 General geotechnical properties
    6.5 Slope design considerations
    6.6 Goldstrike Betze-Post open pit, Nevada: instability in the Carlin Formation
    6.7 Nine Points slope failure at Newmont’s Gold Quarry open pit
    6.8 Overview of open pit experience in cemented (alluvium) gravels found in South-western United States
    6.9 Ministro Hales Mine, Codelco: bench failure in massive gravels

    7 Weak sedimentary mudrocks
    Derek Martin and Pete Stacey
    7.1 Introduction
    7.2 General geological setting
    7.3 Hydrogeology
    7.4 General geotechnical properties
    7.5 Slope design considerations
    7.6 Voorspoed Mine, South Africa: open pit diamond mining in weak mudrock
    7.7 Rio Tinto Minerals Boron operation: design considerations for weak lakebed sedimentary rocks

    8 Weak sedimentary coal, chalk and limestone
    John Simmons, Patrick Ebeling and Peter Stacey
    8.1 Introduction
    8.2 General geological setting
    8.3 Slope design considerations
    8.4 Weak coal measures
    8.5 Chalk and weak limestones

    9 Saprolite: weathered rock and residual soil
    Derek Martin and Pete Stacey
    9.1 Introduction
    9.2 Terminology
    9.3 Weathering processes and geology
    9.4 General geotechnical properties
    9.5 Hydrogeology
    9.6 Slope design considerations
    9.7 Cowal Gold Mine: back analysis
    9.8 Newmont Boddington Gold: slope design optimisation in oxide/saprolite

    10 Soft iron ores and other leached rocks
    Paulo Franca, Teófilo Costa and Peter Stacey
    10.1 Introduction
    10.2 Background
    10.3 Soft iron ores: geology
    10.4 Soft iron ores: geotechnical characteristics (Teófilo Costa and Gilvan Sá)
    10.5 Weathered country rocks
    10.6 Hydrogeology of soft iron ores and associated rocks
    10.7 Leached quartzites and quartzitic sediments
    10.8 Slope performance and case histories

    11 Hydrothermally altered rocks
    Peter Stacey and Derek Martin
    11.1 Introduction
    11.2 General geological setting
    11.3 Geotechnical properties
    11.4 Hydrogeology
    11.5 Slope stability and engineering geology at the Pierina Mine
    11.6 Instability in weak rocks, El Tapado Pit north wall, Yanacocha Operation
    11.7 Lihir Open Pit Mine in argillic materials

    12 Design implementation and operational considerations
    Peter Stacey, Paulo Franca and Geoff Beale
    12.1 Introduction
    12.2 Mine planning
    12.3 Design implementation
    12.4 Surface water control
    12.5 Slope protection
    12.6 Performance assessment and monitoring
    12.7 Ground control management plans
    12.8 Mine closure


    Derek Martin obtained his BSc in 1972 from Memorial University, his MEng from the University of Alberta in 1983 and his PhD from the University of Manitoba in 1993. He has over 35 years of experience in rock engineering associated with rock slopes, tunnels, caverns and dams. His early years were spent on construction sites for major civil, hydroelectric and underground projects. In 1987 he joined AECL, where he directed the geomechanics research at the Underground Research Laboratory in southeastern Manitoba and was senior adviser to the Director of the Canadian Nuclear Fuel Waste Management Program. From 1995-99, he served as Associate Director of the Geomechanics Research Centre at Laurentian University, working on the deep mining projects in the Sudbury basin. Since 2000, Dr Martin has been Professor in Geotechnical Engineering at the University of Alberta, where he holds an NSERC Industrial Research Chair. Dr Martin is a Fellow of the Engineering Institute of Canada and a Fellow of The Canadian Academy of Engineering.

    Peter Stacey has 40 years' experience in all aspects of pit slope and mining geotechnical design, project management and review. He holds a BSc Hons. degree in Geology and 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. In 2003, he formed Stacey Mining Geotechnical Ltd to concentrate on independent review consulting related to the geotechnical aspects of open pit mining. In this capacity, he currently serves as either review consultant or on the Geotechnical Review Board for several large open pit operations. He also performs geotechnical review for a number of mining and consulting companies.