Guidelines for Open Pit Slope Design in Weak Rocks

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

Biography

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.