geotechnical strategy and tactics at anglo platinum's pprust open pit operation, limpopo province

190 Pages·2009·11.03 MB·English

GEOTECHNICAL STRATEGY AND
TACTICS AT ANGLO PLATINUM’S
PPRUST OPEN PIT OPERATION,
LIMPOPO PROVINCE, SOUTH AFRICA

Megan Jane Little

A research report submitted to the Faculty of Engineering and the Built
Environment, University of Witwatersrand, in partial fulfillment of the
requirements for the degree of Master of Science in Engineering

Johannesburg, 2006
DECLARATION

I declare that this research report is my own, unaided work. The content covers work
done at Potgietersrust Platinums, an Anglo Platinum open pit mining operation, by the
author as well as fellow staff members. It is being submitted for the Degree of Master of
Science in Engineering in the University of Witwatersrand, Johannesburg. It has not
been submitted before by the author for any degree or examination in any other
university.

____________________
Megan Jane Little

8th day of December 2006
ABSTRACT

Over the last four years Potgietersrust Platinums (PPRust) has successfully
implemented new geotechnical strategy and tactics to reduce risk, improving safety but
also maximising profitability. A large database of core logging, face mapping and rock
testing has been assembled and used in the slope design process. The data has also been
used for optimising blast designs on a daily basis through the use of a geotechnical
block model. This greatly improves blast fragmentation and therefore loading and
milling efficiencies. Slope management includes a limit blasting programme, daily
visual inspections, and state-of-the-art slope monitoring equipment, namely
GroundProbe radar, Riegl lasers and GeoMoS automated prism monitoring. Slope
optimisation incorporates all the field data, operational controls, cost of failure, full
economic analysis of various slope angles and fault tree analysis. Savings on waste
stripping of hundreds of millions of Rands were gained from the optimisation as slope
angles could be increased due to improved geotechnical knowledge and management.
PPRust’s geotechnical work is considered the benchmark for Anglo American open pit
operations.
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ACKNOWLEDGEMENTS

The use of facilities and the financial assistance of Potgietersrust Platinums
are gratefully acknowledged.

This research report is a great illustration of what teamwork can do. Thanks
must go to the following for their contribution to the work at PPRust:
 PPRust Rock Engineering department for being agents of change
 Frans Benade and Johan Scheepers for their hard work and commitment to slope
monitoring at PPRust
 Alan Bye for his foundational work and new ideas as well as
invaluable guidance and mentoring
 Gert McCarthy for enthusiastic support of all the geotechnical developments
implemented at PPRust
 Peter Nathan for his excellent work, patience tutoring and great sense of humour
 Marcia van Aswegen, Jouri Rodionov and Nick Holleman from SABLE for their
teamwork on the geotechnical database
 Kathleen Hansmann and Hennie Coetzer of Datamine for their work on the
MineMapper3D database
 Peter Terbrugge of SRK for his encouragement and advice
 Julian Venter of SRK for his slope design work and help with the risk analysis
 Prof. Dick Stacey for his supervision of this dissertation and advice

I would also like to thank my friends and family for their constant support.
Lastly, I thank the Lord for His amazing grace!
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CONTENTS

DECLARATION
ABSTRACT
ACKNOWLEDGMENTS
CONTENTS
LIST OF FIGURES
LIST OF TABLES

Page

1 INTRODUCTION 1

2 BACKGROUND

2.1 Location 3
2.2 History 4
2.3 Mining and Processing 5
2.4 Exploration 7
2.5 Conclusion 7

3 GEOLOGY

3.1 Bushveld Igneous Complex 9
3.2 Northern Limb 10
3.3 PPRust Lease Area 12
3.4 Structure 13
3.4.1 Sandsloot pit 14
3.4.2 Zwartfontein South pit 16
3.4.3 PPRust North pit 18
3.5 Geohydrology 19
3.6 Conclusion 20

4 FIELD DATA

4.1 Introduction 21
4.2 Rock Mass Classification Systems 21
4.2.1 Barton et al.’s Rock Quality Index, Q 23
4.2.2 Bieniawski’s Geomechanics Classification 24
4.2.3 Laubscher’s Mining Rock Mass Rating 26
4.2.4 Hoek et al.’s GSI 27
4.3 Core Logging 29
4.3.1 SABLE core logging database 30
4.3.2 Orientated drilling 35
4.4 Face Mapping 36
4.4.1 MineMapper3D 37
4.4.2 SiroVision digital photogrammetry 40
4.5 Rock Testing 43
4.5.1 Laboratory strength tests 44
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Page

4.5.2 Point load field tests 45
4.5.3 Bond work index tests 45
4.5.4 Drop weight tests 46
4.6 Field Data Viewer 47
4.7 Data Integration and Visualisation 48
4.8 Geotechnical Information Location System 50
4.9 Conclusion 51

5 BLOCK MODELLING

5.1 Introduction 52
5.2 Creating a Geotechnical Block Model 52
5.3 Slope Design Application 57
5.4 Blast Design Application 59
5.4.1 Blastability index 59
5.4.2 Fragmentation 64
5.4.3 Application in AutoCAD 67
5.5 Plant Design Application 68
5.6 Conclusion 69

6 SLOPE STABILITY

6.1 Introduction 70
6.2 Failure Mechanisms 70
6.2.1 Planar Failure 71
6.2.2 Wedge Failure 71
6.2.3 Toppling Failure 72
6.3 Factors Affecting Instability 73
6.4 Geotechnical Zones at PPRust 74
6.4.1 Sandsloot pit 74
6.4.2 Zwartfontein South pit 76
6.5 Slope Instability at PPRust 78
6.6 Bench Failure Case Study 80
6.7 Blast Damage 84
6.8 Conclusion 85

7 SLOPE DESIGN

7.1 Introduction 86
7.2 Design Methodology 87
7.2.1 Bieniawski’s system design methodology 87
7.2.2 Stacey’s engineering circle of design 89
7.2.3 Steffen et al.’s risk based design approach 90
7.2.4 PPRust slope design approach 91
7.3 PPRust Slope Design History 92
7.3.1 Sandsloot pit 92
7.3.2 Zwartfontein South pit 94
7.3.3 PPRust North pit 95
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Page

7.4 Slope Analysis Methods 96
7.4.1 Empirical slope design 99
7.4.2 Limit equilibrium 99
7.4.3 Numerical modelling 101
7.5 Rock Fall Analysis 103
7.6 Authorisation Tracking System 105
7.7 Conclusion 107

8 SLOPE MANAGEMENT

8.1 Introduction 108
8.2 Limit Blasting 108
8.2.1 Blasting terminology 108
8.2.2 Limit blasting practices 109
8.2.3 PPRust limit blasting 111
8.3 Visual Inspections 113
8.3.1 Daily inspections 114
8.3.2 Detailed inspections 115
8.3.3 Monthly hazard plan inspections 117
8.2.4 Presplit inspections 119
8.2.5 Foremen inspections 124
8.4 Slope Support 125
8.4.1 Sandsloot footwall ramp gabion wall 126
8.4.2 Sandsloot Bench 11 gabion wall 126
8.4.3 Sandsloot boulders wire meshing 127
8.5 Dewatering 128
8.6 Conclusion 129

9 SLOPE MONITORING

9.1 Introduction 130
9.2 Prism Monitoring 131
9.2.1 GeoMoS automated monitoring at PPRust 132
9.3 Laser Monitoring 135
9.3.1 Riegl laser monitoring at PPRust 136
9.4 Radar Monitoring 139
9.4.1 GroundProbe SSR 139
9.4.2 SSR at PPRust 143
9.5 Seismic Monitoring 145
9.5.1 ISSI microseismic monitoring at PPRust 146
9.5.2 Navachab case study 147
9.6 Groundwater Monitoring 148
9.7 Crackmeters 148
9.8 Slope Monitoring Database 149
9.9 Conclusion 150

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Page

10 SLOPE OPTIMISATION

10.1 Introduction 151
10.2 Risk 151
10.2.1 F-N curves 152
10.2.2 Anglo American standard 153
10.3 Fault and Event Tree Analysis 155
10.3.1 Theory of fault and event tree analysis 155
10.3.2 PPRust fault and event tree analyses 156
10.4 PPRust Slope Optimisation 159
10.4.1 Sandsloot Cut 6 optimisation 160
10.4.2 Zwartfontein South Cut 5 optimisation 164
10.5 Conclusion 165

11 CONCLUSION

REFERENCES
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LIST OF FIGURES

Figure Page

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2.1 Location map of the outcrop of the Bushveld complex and the

Anglo Platinum operations (AP, 2006)
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2.2 Farms and open pits on the PPRust lease area (AP, 2006)
5
2.3 Plan and section views of Sandsloot cutback phases (after Bye,

2003)
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2.4 Grade categories at PPRust (PPRust, 2006)
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2.5 Simple diagram of the PPRust plant feed process (Bye, 2003)
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2.6 Exploration drilling at PPRust as at January 2005 (PPRust, 2006)
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3.1 Location of the 5 limbs and the gravity highs indicating feeder sites

(Sharpe et al., 1981)
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3.2 Non-plume model for the emplacement of the Bushveld Igneous

Complex (Good, 1999)
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3.3 Geology outcrop plan of the Northern limb in the PPRust lease area

(PPRust, 2005)
13
3.4 Sketch of the change in geology over the PPRust lease area

(PPRust, 2005)
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3.5 Structural Interpretation Plan of Sandsloot (SRK, 2003)

3.6 Stereonet of all mapping and orientated logging data collected in
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Sandsloot pit
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3.7 Structural Interpretation Plan of Zwartfontein South (SRK, 2003)
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3.8 Stereonet of all mapping and orientated logging data collected in

Zwartfontein South pit
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3.9 Stereonet of orientated logging for PPRust North
20
3.10 Plan of major rivers in the PPRust lease area
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4.1 Comparison of the four rock mass rating systems used at PPRust
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4.2 Hoek et al.’s GSI chart
30
4.3 Simplified cross-section through Sandsloot open pit and an

exploration borehole showing eight geotechnical units and the scale

of the operation
32
4.4 SABLE Data Warehouse table tree structure at PPRust
32
4.5 ‘Geotech Unit’ log in SABLE Data Warehouse
32
4.6 ‘Joint Sets’ log in SABLE Data Warehouse
33
4.7 Illustration of the tables in SABLE Data Warehouse and the SABLE

Data 1 wraparound
34
4.8 Geotechnical graphical log automatically generated in SABLE
36
4.9 Location of all orientated boreholes drilled at PPRust
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4.10 Illustration of geotechnical zones for a face map in Zwartfontein

South open pit, used for rock mass ratings
38
4.11 Flow of data from the pit, coreyard and lab into a central database
38
4.12 Bench map in MineMapper3D for Sandsloot open pit
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4.13 Example of a 3D facemap in MineMapper3D with digitised

geological contacts, structures and 4 geotechnical zones
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4.14 Example of the input table for geotechnical window mapping data

used to calculate rock mass ratings
40
4.15 Example of data interpretation in MineMapper3D
41
4.16 Method of obtaining photographs for SiroVision
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Figure Page

4.17 Dip and dip directions of a number of joints read off the SiroVision 42
3D image of a small section of the west wall in Sandsloot open pit
4.18 Failure plane measured in SiroJoint imported in Datamine and 43
extrapolated on lower benches and ramps for stability analysis
4.19 FDV form for geotechnical logging at PPRust 48
4.20 FDV form for rock testing results at PPRust 48
4.21 Datamine script developed at PPRust and visual display of 49
boreholes for the proposed PPRust North open pit.
4.22 GILS main form 50
4.23 Technical data tab in GILS showing logging related files and 51
applications
5.1 Flow diagram of the development of the geotechnical block model 53
5.2 First script used to create the block model showing the ore and 54
waste models
5.3 Zwartfontein South Cut 4 geotechnical zone model slice 55
5.4 Simple illustration (not to scale) of interpolation of geotechnical 56
borehole data into a single block in Datamine. Geotechnical zones 1
in BH1 and 3 in BH2 are not used in the interpolation as they fall
outside the search ellipse
5.5 Zwartfontein South Cut 4 block model coloured on IRMR(FF) 56
5.6 Haines and Terbrugge (1991) slope design chart 57
5.7 Visualisation of the MRMR on the pit slopes with the 2nd script 58
5.8 Vertical slice through the Zwartfontein South block model coloured 58
on Slope angle for a 100m stack at FOS=1.2 indicating the west
wall is under-designed 58
5.9 Graph showing tri-linear relation between FF and JPS 61
5.10 Parameters used for Lilly’s BI and their use in Kuz-Ram 63
5.11 Third script used for blast design 64
5.12 Split digital fragmentation analysis (Bye, 2003) 65
5.13 History of ore blast fragmentation curves at Sandsloot pit (Bye, 2003) 66
5.14 RH200 face shovel loading a blasted muckpile into a haul truck 66
5.15 Model bench slice filtered on energy factor (EF) with imported blast 67
boundary overlaid and AutoCAD menus for importing and colour
coding the model
5.16 Customised blast design window in AutoCAD 67
5.17 Configurable blast design pattern overlaid on the block model in 68
AutoCAD
6.1 a) Sketch of a simple planar failure (Hoek and Bray, 1981) and b) 71
its accompanying stereonet (region of failure in yellow)
6.2 a) Sketch of a simple wedge failure (Hoek and Bray 1981) and b) 71
its accompanying stereonet (region of failure in yellow)
6.3 a) Sketch of a simple toppling failure (Hoek and Bray, 1981) and b) 72
its accompanying stereonet (region of failure in yellow)
6.4 Geotechnical zones for Sandsloot open pit 75
6.5 Geotechnical Zone 3 in Zwartfontein South pit 77

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