Teet, R, Vakili, A & de Veth, A 2013, 'Towards developing a more rigorous technique for bench scale slope stability analysis in hard rock', in PM Dight (ed.), Slope Stability 2013: Proceedings of the 2013 International Symposium on Slope Stability in Open Pit Mining and Civil Engineering
, Australian Centre for Geomechanics, Perth, pp. 583-592, https://doi.org/10.36487/ACG_rep/1308_38_Teet
The mining industry is a strong but volatile market that is focused on future growth through expanded production, increased operational efficiency and cost optimisation (Ernst and Young, 2013). As operational expenditure increases and the readily minable ore is extracted, the technical challenges facing mining are becoming more prevalent. With increased depths of open pit operations, the need to minimise the footprint of the mine and limit pre-stripping requires the optimisation of slope geometry and configurations in such a way that extraction is maximised without increasing risk to personnel, equipment or mine life. An essential component of the slope optimisation process is the rigorous geotechnical assessment of the stability of the pit walls at bench, inter-ramp and overall slope scale.
Advancements in computational power and numerical modelling have significantly progressed the analysis of overall slope and inter-ramp scale stability. However the current industry standard methods of bench scale stability analysis still heavily rely on empirical, kinematic and limit equilibrium techniques. These techniques are adequate for scoping and pre-feasibility level projects where the data availability is limited and the confidence in results restricted. In contrast, as the pit develops and progresses into feasibility to implementation stages of development, optimisation becomes a more significant component of the geotechnical assessment and more rigorous analytical methods should be employed.
This paper introduces an improved analytical method that integrates discrete fracture network (DFN) generation and kinematic analyses for bench scale slope stability analysis. Conventional kinematic analyses were conducted on a representative data set and the resulting probability of failure (POF) compared to a POF generated from a calibrated stochastic DFN model. Results showed that the conventional analysis was conservative in nature due to the inability to assess the influence of discontinuity interaction and spacing on the resultant wedge. The authors' experience of recent technical work had also flagged a dissimilarity between the conventional kinematics and real world observations. Additional numerical modelling utilising a pseudo-discontinuum modelling technique was conducted in an attempt to quantify the extent of the conservatism seen in conventional versus alternative methods of bench scale stability assessment.
The ability to incorporate a holistic DFN approach to the assessment of batter scale stability facilitates the optimisation and risk reduction process. The limitations of this alternative method are not fully established and further validation and testing is needed however, potential does exist for the inclusion of DFNs in kinematic bench scale assessments and the subsequent optimisation of slope configurations.
The authors have conducted several technical slope stability assessments for existing open pit operations in Australia. Due to confidentiality arrangements, the operations and specific details cannot be disclosed in this paper. Future work will include a detailed case study.
Carvalho, J.L. (2002) Slope Stability Analysis for Open Pits, Golder Associates Ltd, Canada.
Chiwaye, H.T. (2010) A Comparison of the Limit Equilibrium and Numerical Modelling Approaches to Risk Analysis for Open Pit Mine Slopes, Thesis, University of the Witwatersrand, Johannesburg, South Africa.
Christian, J., Ladd, C. and Baecher, G. (1993) Reliability applied to Slope Stability Analysis, Journal of Geotechnical Engineering, Vol. 120, No 12, pp. 2180–2207.
Christian, J.T. (2004) Geotechnical Engineering Reliability: How Well Do We Know What We Are Doing?, Thirty-Ninth Karl Terzaghi Lecture, 2003, Journal of Geotechnical and Geoenvironmental Engineering, American Society of Civil Engineers, October 2004, Vol. 130(10), pp. 985–1003.
Cundall, P.A. (2002) The replacement of limit equilibrium methods in design with numerical solutions for factor of safety, PowerPoint presentation, Itasca Consulting Group, Inc.
Dershowitz, W.S. (1984) Rock Joint Systems, Ph.D. Dissertation, Massachusetts Institute of Technology, Cambridge, USA.
Duncan, M. (2000) Factors of Safety and Reliability in Geotechnical Engineering, Journal of Geotechnical and Geoenvironmental Engineering, Vol. 126, No. 4, pp. 307–316.
Eberhardt, E. (2003) Rock Slope Stability Analysis-Utilization of Advanced Numerical Techniques, University of British Columbia, April 2003, viewed 1 August 2013,
Ernst and Young (2013) Mining and Metals, Ernst and Young Global Limited, viewed 12 July 2013,
Fenton, G.A. and Griffiths, D.V. (2008) Risk Assessment in Geotechnical Engineering, John Wiley & Sons, Inc., Hoboken, New Jersey, USA.
Franz, J. Cai, Y. and Hebblewhite, B. (2007) Numerical Modelling of Composite Large Scale Rock Slope Failure Mechanisms Dominated by Major Geological Structures, 11th ISRM Congress, Lisbon, Portugal, Vol. 1, pp. 633–636.
Golder Associates (2011) User Manual: Fracman 7, Golder Associates Inc., 390 p.
Golder Associates (2013) Fracman Software, Version 7.4., Golder Associates Inc., Washington.
Hoek, E. Read, J. Karzulovic, A. and Chen, Z.Y. (2000) Rock slopes in Civil and Mining Engineering, in Proceedings International Conference on Geotechnical and Geological Engineering (GeoEng2000), 19–24 November 2000, Melbourne. Viewed 1 August 2013,
Itasca (2012) FLAC3D 5.0 – Fast Lagrangian Analysis of Continua, Version 5.0 User’s Guide, Itasca Consulting Group, Inc., Minneapolis.
Krahn, J. (2003) The 2001 R.M. Hardy Lecture: The limits of limit equilibrium analyses, Canadian Geotechnical Journal, Canadian Science Publishing, Vol. 40, pp. 643–660.
Mostyn, G.R. and Soo, S. (1992) The Effect of Autocorrelation on the Probability of Failure of Slopes, in Proceeding 6th Australia New Zealand Conference on Geomechanics: Geotechnical Risk, Christchurch, New Zealand. pp. 542–546.
Read, J. and Stacey, P. (2009) Guidelines for Open Pit Slope Design, CSIRO Publishing, Collingwood, 496 p.
Rocscience (2005) Swedge version 5.0, 3D Surface Wedge Analysis for Slopes software,
Simmonds, J. and Simpson, P.J. (2006) Composite failure mechanisms in coal measures rock masses – myths and reality, in Proceedings International Symposium on Stability of Rock Slopes in Open Pit Mining and Civil Engineering, The South African Institute of Mining and Metallurgy, Johannesburg, Vol. 106, pp. 459–470.
Stacey, T.R. (2006) Design – A Strategic Issue, in Proceedings Second International Seminar on Strategic versus Tactical Approaches to Mining, 8–10 March 2006, Perth, Australia, Australian Centre for Geomechanics, Perth, Section 4, pp. 1–14.
Stead, D., Eberhardt, E. and Coggan, J.S. (2006) Developments in the Characterization of Complex Rock Slope Deformation and Failure Using Numerical Modelling Techniques, Engineering Geology, Vol. 83, pp. 217–235.
Valdivia, C., and Lorig, L. (2000) Slope Stability at Escondida Mine, Slope Stability in Surface Mining, Ch. 17, W.A. Hustrulid, M.K. McCarter and D.J.A. Van Zyl, Society of Mining, Metallurgy and Exploration, Inc., Littleton, USA, pp. 153–162.
Wyllie, D.C. and Mah, C.W. (2004) Rock slope engineering (Civil and Mining) 4th Edition, The Institute of Mining and Metallurgy, Abingdon, UK, pp. 129–217.
Whitman, R. (1984) Evaluating Calculated Risk in Geotechnical Engineering, Journal of Geotechnical Engineering, Vol. 110, No 2, pp. 145–188.