Towards developing a more rigorous technique for bench scale slope stability analysis in hard rock

Authors: Teet, R; Vakili, A; de Veth, A Download Paper

DOI https://doi.org/10.36487/ACG_rep/1308_38_Teet

Cite As:
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



Abstract:
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.

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