G u i d e l i n e s f o r Guidelines for Evaluating Water in Pit Slope Stability is a comprehensive account of the E hydrogeological procedures that should be followed when performing open pit slope stability v Evaluating Water in Pit Slope Stability design studies. Created as an outcome of the large open Pit (loP) project, an international a l research and technology transfer project on the stability of rock slopes in open pit mines, u this book expands on the hydrogeological model chapter in the loP project’s previous book a EdItORS: GEOff BEalE and JOhn REad Guidelines for Open Pit Slope Design (read & stacey, 2009; CSIRO PuBlishinG). t i n the book comprises six sections which outline the latest technology and best practice procedures g for hydrogeological investigations. the sections cover: the framework used to assess the effect G of water in slope stability; how water pressures are measured and tested in the field; how a W u conceptual hydrogeological model is prepared; how water pressures are modelled numerically; a i how slope depressurisation systems are implemented; and how the performance of a slope d t depressurisation program is monitored and reconciled with the design. e e r Guidelines for Evaluating Water in Pit Slope Stability offers slope design practitioners a road map l that will help them decide how to investigate and treat water pressures in pit slopes. it provides in i n guidance and essential information for mining and civil engineers, geotechnical engineers, P engineering geologists and hydrogeologists involved in the investigation, design and construction e i of stable rock slopes. t s S f l o o p r e S t a b i l i t y Editors: GEoff BEalE John rEad Guidelines for Evaluating Final JK.indd 1 14/11/13 2:08 PM G U I D E L I N E S F O R Evaluating Water in Pit Slope Stability This page intentionally left blank 090502•Australian Vertebrates.in2 2 28/11/05 1:36:32 PM G U I D E L I N E S F O R Evaluating Water in Pit Slope Stability EDITORS: GEOFF BEALE AND JOHN READ © CSIRO 2013 All rights reserved. Except under the conditions described in the Australian Copyright Act 1968 and subsequent amendments, no part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, duplicating or otherwise, without the prior permission of the copyright owner. Contact CSIRO PUBLISHING for all permission requests. National Library of Australia Cataloguing-in-Publication entry Guidelines for evaluating water in pit slope stability/edited by John Read and Geoff Beale. 9780643108356 (hardback) 9780643108363 (epdf) 9780643108370 (epub) Includes bibliographical references and index. Strip mining – Planning. Strip mining – Design and construction. Slopes (Soil mechanics) Landslides. Read, John Russell Lee, 1939– editor. Beale, Geoff, 1954– editor. 622.292 Published exclusively in Australia and New Zealand by CSIRO PUBLISHING 150 Oxford Street (PO Box 1139) Collingwood VIC 3066 Australia Telephone: +61 3 9662 7666 Local call: 1300 788 000 (Australia only) Fax: +61 3 9662 7555 Email: [email protected] Website: www.publish.csiro.au Published exclusively throughout the world (excluding Australia and New Zealand) by CRC Press/Balkema, with ISBN 978-1-138-00134-3 CRC Press/Balkema P.O. Box 11320 2301 EH Leiden The Netherlands Tel: +31 71 524 3080 Website: www.crcpress.com Front cover: Diavik Diamond Mine, Northwest Territories, Canada (courtesy Diavik Diamond Mines Inc, Yellowknife, Canada) Set in 10/12 Adobe Minion Pro and Optima Cover and text design by James Kelly Typeset by Desktop Concepts Pty Ltd, Melbourne Index by Indexicana Printed in China by 1010 Printing International Ltd Disclaimer CSIRO PUBLISHING publishes and distributes scientific, technical and health science books, magazines and journals from Australia to a worldwide audience and conducts these activities autonomously from the research activities of the Commonwealth Scientific and Industrial Research Organisation (CSIRO). The views expressed in this publication are those of the author(s) and do not necessarily represent those of, and should not be attributed to, the publisher, CSIRO or any of the Large Open Pit (LOP) project sponsors. The information in this book is general in nature and not intended for any particular situation; to the extent possible, all warranties or guarantees, express or implied, are excluded, including any warranty that reliance on information in this publication will produce any particular result. No liability is accepted by the publisher or any LOP project sponsor for any technical or other errors or omissions. The reader/user acknowledges that information in this publication may be incomplete and must make its own inquiries as to the suitability of information in this publication for its particular circumstances; and accepts all risks and responsibility for losses, damages, costs and other consequences resulting directly or indirectly from using this information. Original print edition The paper this book is printed on is in accordance with the rules of the Forest Stewardship Council®. 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Contents Preface and acknowledgements xiii Introduction 1 John Read, Geoff Beale, Marc Ruest and Martyn Robotham 1 Scope of LOP project hydrogeological studies 1 2 General impact of water on mining 4 2.1 Water management issues 4 2.2 Consequences of mining below the water table 6 2.3 General goals for the water-control program 6 3 Cost of managing water in slope stability 8 3.1 Introduction 8 3.2 Cost–benefit analysis 8 3.3 An example of managing early dewatering costs 10 3.4 An example of large-scale cost–benefit analysis for pit slope depressurisation 13 4 Goals of managing water in slope stability 14 4.1 Opportunities 14 4.2 Passive pore pressure control 14 4.3 Active pore pressure control 15 4.4 Making the decision to implement an active program 15 5 General planning for mine water management 16 1 Framework: assessing water in slope stability 19 Geoff Beale, Michael Price and John Waterhouse 1.1 Fundamental parameters 19 1.1.1 Porosity and storage properties 19 1.1.2 Permeability and transport properties 24 1.1.3 Pore pressure 34 1.1.4 Head and pressure conditions 35 1.1.5 Controls on pore pressure 38 1.1.6 The role of water pressure in slope stability 41 1.2 The hydrogeological model 45 1.2.1 Basic regimes 45 1.2.2 Geology 45 1.2.3 Hydrology 48 1.2.4 Hydraulic controls 49 1.3 Managing water in open pit mines 49 1.3.1 Key factors affecting the water-management program 49 1.3.2 General mine dewatering 51 1.3.3 Pit slope depressurisation and general mine dewatering 52 1.3.4 Steps required for implementing a slope depressurisation program 56 1.3.5 Mine water balance 57 1.3.6 Mine closure considerations 58 vi Guidelines for Evaluating Water in Pit Slope Stability 2 Site characterisation 65 Greg Doubek, Ashley Creighton, Jeremy Dowling, Michael Price and Mark Hawley 2.1 Planning field programs 65 2.1.1 Introduction 65 2.1.2 Scale of the investigation 68 2.1.3 Early-stage investigation 69 2.1.4 Integrating the design process 69 2.1.5 Required effort based on project level 73 2.1.6 Planning for a Greenfield mine development 78 2.1.7 Planning for a Brownfield site development 79 2.1.8 Environmental baseline studies 80 2.1.9 Water management practices during the field investigation program 81 2.2 Implementing field programs 82 2.2.1 Background 82 2.2.2 Drilling methods 83 2.2.3 ‘Piggy-backing’ of data collection 83 2.2.4 Dedicated hydrogeological drilling programs 83 2.2.5 Single-hole testing methods 88 2.2.6 Monitoring installations 96 2.2.7 Downhole geophysical logging 107 2.2.8 Cross-hole and multi-hole testing 119 2.2.9 Water quality testing 126 2.2.10 Pilot drainage trials 128 2.3 Presentation, analysis and storage of data 129 2.3.1 Types of data 129 2.3.2 Display of time-series monitoring data 130 2.3.3 Analysis of one-off data 140 2.3.4 Levels of data analysis for a typical development program 145 2.3.5 Databases 149 3 Preparing a conceptual hydrogeological model 153 Geoff Beale, Pete Milmo, Mark Raynor, Michael Price and Frederic Donzé 3.1 Introduction 153 3.1.1 Background 153 3.1.2 What is a conceptual model? 153 3.1.3 Development of a sector-scale model 153 3.1.4 Available data 155 3.2 Components of the conceptual model 155 3.2.1 Components of a larger scale conceptual model 155 3.2.2 The ‘A-B-C-D’ concept of fracture flow 156 3.2.3 Components of the sector-scale conceptual model 157 3.3 Research outcomes from Diavik 158 3.3.1 Background 158 3.3.2 Diavik site setting 159 3.3.3 Effects of blasting 166 3.3.4 Influence of freeze-back 169 3.3.5 Responses to changes in hydraulic stress 172 3.3.6 Overall interpretation of the Diavik results 175 3.4 Discrete Fracture Network (DFN) modelling 179 3.4.1 DFN development 179 Contents vii 3.4.2 Stochastic realisations of the DFN 180 3.4.3 The DFN as the basis for a groundwater flow model 180 3.5 Summary of case studies 181 3.5.1 Introduction 181 3.5.2 Diavik North-west wall: an interconnected rock mass that is strongly influenced by recharge and discharge boundaries 182 3.5.3 Escondida East wall: alteration in the fracture network and groundwater recharge from outside the pit crest 182 3.5.4 Chuquicamata, a very low-permeability system with little recharge or discharge 183 3.5.5 Antamina West wall: drainage of the slopes inhibited by structural barriers 183 3.5.6 Jwaneng East wall: poorly permeable but highly interconnected shale sequence 184 3.5.7 Cowal 184 3.5.8 Layered limestone sequence in Nevada, USA 184 3.5.9 Whaleback South wall 184 3.6 Factors contributing to a slope-scale conceptual model 185 3.6.1 Regimes 185 3.6.2 The influence of geology on the conceptual model 185 3.6.3 Hydrological input: recharge to the slope domain 189 3.6.4 Hydrological output: the role of discharge in slope depressurisation 192 3.6.5 Hydraulics 194 3.6.6 Deformation 201 3.6.7 Transient pore pressures 209 3.7 Conclusions 211 3.7.1 Key factors 211 3.7.2 Hydrogeological setting 211 3.7.3 Nature of the conceptual model 213 4 Numerical model 215 Loren Lorig, Jeremy Dowling, Geoff Beale and Michael Royle 4.1 Planning a numerical model 215 4.1.1 Background 215 4.1.2 Scale-specific application of the model 217 4.1.3 Focussing the model on the slope design process 220 4.1.4 General planning considerations 220 4.1.5 Timeframe and budget considerations 223 4.1.6 Modelling workflow 225 4.1.7 Data requirements and sources 225 4.2 Development of numerical groundwater flow models 229 4.2.1 Steps required for model development 229 4.2.2 Determining model geometry 231 4.2.3 Setting the model domain and boundaries 239 4.2.4 Defining the mesh or grid size 244 4.2.5 Determining whether to run steady-state, transient or undrained simulations 246 4.2.6 Determining whether the use of an equivalent porous medium (EPM) code is adequate 249 4.2.7 Selecting the appropriate time steps (stress periods) 251 4.2.8 Deciding whether a coupled modelling approach is required 252 viii Guidelines for Evaluating Water in Pit Slope Stability 4.2.9 Incorporating active drainage measures into the model 254 4.2.10 Calibrating the model 254 4.2.11 Interpreting model results 258 4.2.12 Validating model results 261 4.2.13 Using the model for operational planning 262 4.3 Use of pore pressures in numerical stability analyses 262 4.3.1 Background 262 4.3.2 How pore pressure modelling differs from stability analysis 264 4.3.3 Methods for inputting pore water pressure 264 4.3.4 Pore pressure profiles versus phreatic surface (water table) assumptions 265 4.3.5 Integration of the hydrogeology and geotechnical models 269 4.3.6 Model codes 271 4.3.7 Requirements for groundwater input to the slope design 272 4.3.8 Transferring output from the hydrogeological model to the geotechnical model 273 4.3.9 Input of transient pore pressures to the slope design model 275 4.3.10 Introducing Slope Model 277 5 Implementation of slope depressurisation systems 279 Geoff Beale, John De Souza, Rod Smith and Bob St Louis 5.1 Planning slope depressurisation systems 279 5.1.1 General factors for planning 279 5.1.2 Integration with mine planning 283 5.1.3 Development of targets 286 5.2 Implementing a groundwater-control program 291 5.2.1 Types of control systems 291 5.2.2 Passive drainage into the pit 295 5.2.3 Horizontal drain holes 296 5.2.4 Vertical and steep-angled drains 312 5.2.5 Design and installation of pumping wells 316 5.2.6 Drainage tunnels 333 5.2.7 Opening up drainage pathways by blasting 337 5.2.8 Protection of in-pit dewatering installations 338 5.2.9 Organisational structure 343 5.3 Control of surface water 345 5.3.1 Goals of the surface water management program 345 5.3.2 Sources of surface water 346 5.3.3 Control of surface water 346 5.3.4 Estimating flow rates 352 5.3.5 Control of recharge 353 5.3.6 In-pit stormwater management and maintenance 353 5.3.7 Maintenance of surface water control systems 355 5.3.8 Integration of in-pit groundwater and surface water management 357 5.3.9 Protection of the slope from erosion 360 6 Monitoring and design reconciliation 363 Chris Lomberg, Ian Ream, Rory O’Rourke and John Read 6.1 Monitoring 363 6.1.1 Overview 363 6.1.2 Components of the monitoring system 363 Contents ix 6.1.3 Setting up monitoring programs 366 6.1.4 Water level monitoring 370 6.1.5 Telemetry 372 6.1.6 Display of monitoring results 373 6.2 Performance assessment 376 6.2.1 Overview 376 6.2.2 Operational groundwater flow model 377 6.2.3 Process for ongoing assessment 378 6.3 Water risk management 379 6.3.1 Overview 379 6.3.2 Process of risk analysis 379 6.3.3 Risk assessment methodology 380 6.3.4 Identifying the risks 383 6.3.5 Defining the consequences 386 6.3.6 Implementing a water risk management program 387 6.3.7 Value of water risk management 389 Appendix 1 Hydrogeological background to pit slope depressurisation 391 1 Darcy’s law 391 2 Head and pressure 391 3 Darcy’s law in field situations 392 4 Flow in three dimensions 394 Appendix 2 Guidelines for field data collection and interpretation 398 1 Summary of drilling methods commonly used in mine hydrogeology investigations 398 1.1 Direct push method 398 1.2 Auger drilling 398 1.3 Sonic drilling 398 1.4 Cable tool drilling 398 1.5 Rotary core drilling 398 1.6 Conventional mud rotary drilling 399 1.7 Conventional air/foam drilling 399 1.8 Flooded reverse-circulation drilling 399 1.9 Dual-tube reverse-circulation (RC) drilling with air 400 1.10 Horizontal, angled and directional drilling 401 2 Standardised hydrogeological logging form for use with RC drilling 401 3 Interpretation of data collected while RC drilling 401 3.1 Airlift pumping 401 3.2 Submergence 403 3.3 Examples of pilot hole comparison and data interpretation 405 4 Guidelines for drill-stem injection tests 408 5 Guidelines for running and interpreting hydraulic tests 410 5.1 Single-hole variable-head tests 410 5.2 Packer tests 412 5.3 Pumping tests 418 6 Guidelines for the installation of grouted-in vibrating wire piezometer strings 424 6.1 Drilling methods 424