Authors: Rogers, S; Valerio, M; Fogel, Y; Byrne, C; Ojeda, P

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Rogers, S, Valerio, M, Fogel, Y, Byrne, C & Ojeda, P 2023, 'Evaluation of inter-ramp scale non-daylighting wedges using a discrete fracture network-based method', in PM Dight (ed.), SSIM 2023: Third International Slope Stability in Mining Conference, Australian Centre for Geomechanics, Perth, pp. 951-964,

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Open pit slopes that consist of medium to strong, moderately to highly fractured rock mass present challenges when inter-ramp scale analysis and design are considered. Conventional kinematic analyses fail to capture the structural complexity of the slope over stacks of benches. Limit equilibrium approaches can incorporate a simple rock mass fabric, but they are typically not able to represent multiple structural sets or complex rock block geometries. Numerical stress models provide a more rigorous approach but are time consuming to set up, typically have long simulation times and are impractical for evaluating the impact of inherent structural uncertainty on slope stability. It is this last aspect that is often critically important, yet difficult to evaluate. Discrete fracture network (DFN) methods provide an effective solution for handling structural complexity and uncertainty, with a stochastic modelling approach that allows complex rock block geometries to be generated and the kinematics evaluated. However, most of the multi-bench-scale blocks formed comprise non-daylighting wedges (NDWs) that are stable because they occur behind or beside a buttress of rock mass that stabilises the block, rendering the simple kinematic solution ineffective. To overcome this challenge,a custom approach was developed for evaluating the stability of these NDWs. The approach can efficiently analyse a wide range of discontinuity strengths, rock mass strengths and pore pressure conditions, allowing critical controls on slope stability to be identified and opportunities for slope design optimisation to be evaluated based upon Probability of Failure (PoF) criteria. This paper provides an update on the DFN-3DPOF method, based upon several years of application. It describes the DFN approach and the block stability solution, when to use this method and when not to, the handling of NDW geometries and how the approach has contributed to advancing inter-ramp analysis and design.

Keywords: inter-ramp slope stability, discrete fracture network, non-daylighting wedges, 3D probabilistic analysis

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