Cover

Contents

Preface and acknowledgements

INTRODUCTION

1 Scope of LOP project hydrogeological studies

2 General impact of water on mining

2.1 Water management issues

2.2 Consequences of mining below the water table

2.3 General goals for the water-control program

3 Cost of managing water in slope stability

3.1 Introduction

3.2 Cost–benefit analysis

3.3 An example of managing early dewatering costs

3.4 An example of large-scale cost–benefit analysis for pit slope depressurisation

4 Goals of managing water inslope stability

4.1 Opportunities

4.2 Passive pore pressure control

4.3 Active pore pressure control

4.4 Making the decision to implement anactive program

5 General planning for mine watermanagement

1 FRAMEWORK: ASSESSING WATER IN SLOPE STABILITY

1.1 Fundamental parameters

1.1.1 Porosity and storage properties

1.1.2 Permeability and transport properties

1.1.3 Pore pressure

1.1.4 Head and pressure conditions

1.1.5 Controls on pore pressure

1.1.6 The role of water pressure in slopestability

1.2 The hydrogeological model

1.2.1 Basic regimes

1.2.2 Geology

1.2.3 Hydrology

1.2.4 Hydraulic controls

1.3 Managing water in open pitmines

1.3.1 Key factors affecting the water management program

1.3.2 General mine dewatering

1.3.3 Pit slope depressurisation and general mine dewatering

1.3.4 Steps required for implementing a slope depressurisation program

1.3.5 Mine water balance

1.3.6 Mine closure considerations

2 SITE CHARACTERISATION

2.1 Planning field programs

2.1.1 Introduction

2.1.2 Scale of the investigation

2.1.3 Early-stage investigation

2.1.4 Integrating the design process

2.1.5 Required effort based on projectlevel

2.1.6 Planning for a Greenfield mine development

2.1.7 Planning for a Brownfield site development

2.1.8 Environmental baseline studies

2.1.9 Water management practices during the field investigation program

2.2 Implementing field programs

2.2.1 Background

2.2.2 Drilling methods

2.2.3 ‘Piggy-backing’ of data collection

2.2.4 Dedicated hydrogeological drilling programs

2.2.5 Single-hole testing methods

2.2.6 Monitoring installations

2.2.7 Downhole geophysical logging

2.2.8 Cross-hole and multi-hole testing

2.2.9 Water quality testing

2.2.10 Pilot drainage trials

2.3 Presentation, analysis andstorage of data

2.3.1 Types of data

2.3.2 Display of time-series monitoring data

2.3.3 Analysis of one-off data

2.3.4 Levels of data analysis for a typical development program

2.3.5 Databases

3 PREPARING A CONCEPTUAL HYDROGEOLOGICAL MODEL

3.1 Introduction

3.1.1 Background

3.1.2 What is a conceptual model?

3.1.3 Development of a sector-scale model

3.1.4 Available data

3.2 Components of the conceptual model

3.2.1 Components of a larger scale conceptual model

3.2.2 The ‘A-B-C-D’ concept of fracture flow

3.2.3 Components of the sector-scale conceptual model

3.3 Research outcomes from Diavik

3.3.1 Background

3.3.2 Diavik site setting

3.3.3 Effects of blasting

3.3.4 Influence of freeze-back

3.3.5 Responses to changes in hydraulic stress

3.3.6 Overall interpretation of the Diavik results

3.4 Discrete Fracture Network(DFN) modelling

3.4.1 DFN development

3.4.2 Stochastic realisations of the DFN

3.4.3 The DFN as the basis for a groundwater flow model

3.5 Summary of case studies

3.5.1 Introduction

3.5.2 Diavik North-west wall: an interconnected rock mass that is stronglyinfluenced by recharge and dischargeboundaries

3.5.3 Escondida East wall: alteration in the fracture network and groundwater rechargefrom outside the pit crest

3.5.4 Chuquicamata, a very low-permeability system with little rechargeor discharge

3.5.5 Antamina West wall: drainage of the slopes inhibited by structural barriers

3.5.6 Jwaneng East wall: poorly permeable but highly interconnected shale sequence

3.5.7 Cowal

3.5.8 Layered limestone sequence in Nevada, USA

3.5.9 Whaleback South wall

3.6 Factors contributing to a slope scale conceptual model

3.6.1 Regimes

3.6.2 The influence of geology on the conceptual model

3.6.3 Hydrological input: recharge to the slope domain

3.6.4 Hydrological output: the role of discharge in slope depressurisation

3.6.5 Hydraulics

3.6.6 Deformation

3.6.7 Transient pore pressures

3.7 Conclusions

3.7.1 Key factors

3.7.2 Hydrogeological setting

3.7.3 Nature of the conceptual model

4 NUMERICAL MODEL

4.1 Planning a numerical model

4.1.1 Background

4.1.2 Scale-specific application of themodel

4.1.3 Focussing the model on the slope design process

4.1.4 General planning considerations

4.1.5 Timeframe and budget considerations

4.1.6 Modelling workflow

4.1.7 Data requirements and sources

4.2 Development of numerical groundwater flow models

4.2.1 Steps required for model development

4.2.2 Determining model geometry

4.2.3 Setting the model domain andboundaries

4.2.4 Defining the mesh or grid size

4.2.5 Determining whether to run steadystate, transient or undrained simulations

4.2.6 Determining whether the use of anequivalent porous medium (EPM) code isadequate

4.2.7 Selecting the appropriate time steps(stress periods)

4.2.8 Deciding whether a coupled modelling approach is required

4.2.9 Incorporating active drainage measures into the model

4.2.10 Calibrating the model

4.2.11 Interpreting model results

4.2.12 Validating model results

4.2.13 Using the model for operational planning

4.3 Use of pore pressures innumerical stability analyses

4.3.1 Background

4.3.2 How pore pressure modelling differs from stability analysis

4.3.3 Methods for inputting pore water pressure

4.3.4 Pore pressure profiles versus phreatic surface (water table) assumptions

4.3.5 Integration of the hydrogeology and geotechnical models

4.3.6 Model codes

4.3.7 Requirements for groundwater input to the slope design

4.3.8 Transferring output from the hydrogeological model to the geotechnicalmodel

4.3.9 Input of transient pore pressures tothe slope design model

4.3.10 Introducing Slope Model

5 IMPLEMENTATION OF SLOPE DEPRESSURISATION SYSTEMS

5.1 Planning slope depressurisation systems

5.1.1 General factors for planning

5.1.2 Integration with mine planning

5.1.3 Development of targets

5.2 Implementing a groundwater controlprogram

5.2.1 Types of control systems

5.2.2 Passive drainage into the pit

5.2.3 Horizontal drain holes

5.2.4 Vertical and steep-angled drains

5.2.5 Design and installation of pumping wells

5.2.6 Drainage tunnels

5.2.7 Opening up drainage pathways byblasting

5.2.8 Protection of in-pit dewatering installations

5.2.9 Organisational structure

5.3 Control of surface water

5.3.1 Goals of the surface water management program

5.3.2 Sources of surface water

5.3.3 Control of surface water

5.3.4 Estimating flow rates

5.3.5 Control of recharge

5.3.6 In-pit stormwater management andmaintenance

5.3.7 Maintenance of surface water control systems

5.3.8 Integration of in-pit groundwater and surface water management

5.3.9 Protection of the slope from erosion

6 MONITORING AND DESIGN RECONCILIATION

6.1 Monitoring

6.1.1 Overview

6.1.2 Components of the monitoring system

6.1.3 Setting up monitoring programs

6.1.4 Water level monitoring

6.1.5 Telemetry

6.1.6 Display of monitoring results

6.2 Performance assessment

6.2.1 Overview

6.2.2 Operational groundwater flow model

6.2.3 Process for ongoing assessment

6.3 Water risk management

6.3.1 Overview

6.3.2 Process of risk analysis

6.3.3 Risk assessment methodology

6.3.4 Identifying the risks

6.3.5 Defining the consequences

6.3.6 Implementing a water risk management program

6.3.7 Value of water risk management

Appendix 1 Hydrogeological background to pit slope depressurisation

1 Darcy’s law

2 Head and pressure

3 Darcy’s law in field situations

4 Flow in three dimensions

Appendix 2 Guidelines for field data collection and interpretation

1 Summary of drilling methods commonly used in mine hydrogeology investigations

1.1 Direct push method

1.2 Auger drilling

1.3 Sonic drilling

1.4 Cable tool drilling

1.5 Rotary core drilling

1.6 Conventional mud rotary drilling

1.7 Conventional air/foam drilling

1.8 Flooded reverse-circulation drilling

1.9 Dual-tube reverse-circulation (RC)drilling with air

1.10 Horizontal, angled and directional drilling

2 Standardised hydrogeological logging form for use with RC drilling

3 Interpretation of data collected while RC drilling

3.1 Airlift pumping

3.2 Submergence

3.3 Examples of pilot hole comparison and data interpretation

4 Guidelines for drill-stem injection tests

5 Guidelines for running and interpreting hydraulic tests

5.1 Single-hole variable-head tests

5.2 Packer tests

5.3 Pumping tests

6 Guidelines for the installation of grouted-in vibrating wire piezometerstrings

6.1 Drilling methods

6.2 Depth setting for vibrating wire sensors

6.3 Installation of multi-level VWPs using the guide-tremie pipe method

6.4 Installation of multi-level VWPs using the wireline method

6.5 Installation of VWP sensors inhorizontal or positive inclined drill holes

6.6 Installation of multi-level VWPs in underground boreholes

6.7 Prefabricated multi-level VWP installations

6.8 Commonly used grout mix

7 Westbay multi-level system

7.1 Installation

7.2 Operation

Appendix 3 Case study: Diavik North-west wall

1 Background

1.1 Location

1.2 The North-west wall, A154 Pit

1.3 Climate

1.4 Hydrogeological setting

1.5 Depressurisation of the North-west wall

1.6 Piezometer installations in the North- west wall

2 Hydrograph analysis

2.1 Overview

2.2 Analysis of specific events

3 DFN modelling

3.1 DFN-based data analysis

3.2 DFN model building

3.3 DFN model validation

3.4 Summary

Appendix 4 Case studies: Escondida East wall; Chuquicamata; Radomiro Tomic; Antamina West wall; Jwaneng; Cowal; Whaleback South wall; La Quinua (Yanacocha)

1 Escondida East wall

1.1 Background

1.2 Geology and hydrostratigraphy

1.3 Dewatering and depressurisation

1.4 Conceptual hydrogeological model

1.5 Discussion

2 Chuquicamata

2.1 Background

2.2 Geology and hydrostratigraphy

2.3 Drain hole results

2.4 Conceptual hydrogeological model

2.5 Discussion

3 Radomiro Tomic

3.1 Background

3.2 Response to mining pushbacks in the south-east area of the pit

3.3 Piezometric responses in the West wall

3.4 Responses in the northern sector of the West wall

4 Antamina West wall

4.1 Background

4.2 Geology and hydrostratigraphy

4.3 Dewatering and depressurisation

4.4 Conceptual hydrogeological model

4.5 Discussion

5 Jwaneng Diamond Mine Southeast wall

5.1 Background

5.2 Geology and hydrostratigraphy

5.3 Dewatering program

5.4 Slope depressurisation

5.5 Discussion

6 Cowal Gold Mine (CGM)

6.1 Introduction

6.2 Initial instability of the East high wall

6.3 Geology and geotechnical domains

6.4 Geotechnical considerations for thesoft oxide zone

6.5 Hydrogeological results

6.6 Prediction of pore pressures

6.7 Depressurisation response

6.8 Dewatering well pumping and recoverytest

6.9 Horizontal drainage response examplefor ultimate slope depressurisation

7 Whaleback South wall

7.1 Dewatering of the main ore body

7.2 Conditions in the South wall

7.3 Interpretation

8 La Quinua, Peru

8.1 General site setting

8.2 General mine dewatering

8.3 Phase 2C area

8.4 East high wall

8.5 Remediation plan

Appendix 5 Cases studies for numerical modelling

Case study 1: Numerical modellingof the North-west wall of the DiavikA154 pit

1.1 Analysis of the DFN

1.2 Use of the EPM Model

1.3 Conclusions

Case study 2: Numerical modellingof the marl sequence at the Cobre Las Cruces Mine, Andalucía, Spain

2.1 Background

2.2 Model development

2.3 Conclusions

Appendix 6 The lattice formulation and the Slope Model code

1 The lattice formulation

2 Features of the lattice approach

3 Example application

4 Validation of Slope Model using experimental data from Coaraze test site

4.1 Geometry

4.2 Boundary conditions

4.3 Building the model

4.4 Simulation results

4.5 Conclusions

Appendix 7 Lessons learnt and basic guidelines to monitoring for general dewatering

1 Introduction

2 Water level monitoring

2.1 Reasons for monitoring

2.2 Water level measurement – practicalguidelines

2.3 Monitoring frequency

2.4 Location of piezometers

2.5 Monitoring of pumping rates

2.6 Monitoring for hydrochemicalfingerprinting

3 Summary and conclusions

Symbols

Abbreviations

Glossary

References

Index