On double-wedge and bi-planar failure mechanisms in waste rock dumps and heap leach facilities

Authors: Arrieta, M; Bar, N Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2535_23

Cite As:
Arrieta, M & Bar, N 2025, 'On double-wedge and bi-planar failure mechanisms in waste rock dumps and heap leach facilities', in JJ Potter & J Wesseloo (eds), SSIM 2025: Fourth International Slope Stability in Mining Conference, Australian Centre for Geomechanics, Perth, https://doi.org/10.36487/ACG_repo/2535_23



Abstract:
Double-wedge and other complex failure mechanisms in high-end waste dumps and heap-leach facilities remain under-recognised hazards, particularly where dumps reach great heights on sloping foundations. Numerous catastrophic incidents over the past three decades confirm that these events involve an “active” wedge driving a “passive” wedge that has not yet fully mobilised, permitting large, non-brittle deformations. A double-wedge failure is comprised of two kinematically linked wedges bounded by intersecting shear planes, with the upper block progressively mobilising the lower block. Conventional limit-equilibrium assessments can underestimate the associated risk by assigning a single Factor of Safety that masks this active–passive contrast. This paper tests the hypothesis that double-wedge (active–passive block) and bi-planar failures can be reliably distinguished, and their risks semi-quantified by staged finite-element (FE) and finite-difference (FD) backanalysis. The objectives are to: (1) formalise diagnostic criteria that capture partial versus uniform shear-mobilisation, (2) evaluate the criteria through two documented case studies, and (3) translate the findings into practical mitigation strategies. High-resolution crack mapping and drone-based displacement monitoring reveal wedge propagation toward the crest, while FE/FD models reproduce these movements and quantify the safety-factor. The case studies show that dumps exceeding about 200 m typically initiate doublewedge failure at roughly two-thirds of their height, and that steeper basal beds in heap leach facilities accelerate dual failure-plane formation. Objective 2 is therefore confirmed; double-wedge interaction frequently governs large-scale instability. Systematic instrumentation and targeted inspections, linked to performance-based key performance indicators, enable early detection and warning of the partial mobilisation signature. Objective 3 translates these insights into an integrated mitigation strategy that combines selective placement of weaker material, incremental geometry refinements and disciplined construction-and-monitoring routines, demonstrably lowering collapse potential in challenging geotechnical settings.

Keywords: double-wedge, bi-planar, high-end waste dumps, heap leach, stability analysis

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