Preventing pit wall failure through early detection monitoring, geotechnical analysis and execution of a toe-stabilisation buttress

Authors: Jonsson, V; Nairn, L Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2335_58

Cite As:
Jonsson, V & Nairn, L 2023, 'Preventing pit wall failure through early detection monitoring, geotechnical analysis and execution of a toe-stabilisation buttress', in PM Dight (ed.), SSIM 2023: Third International Slope Stability in Mining Conference, Australian Centre for Geomechanics, Perth, pp. 831-852, https://doi.org/10.36487/ACG_repo/2335_58



Abstract:
Multi-batter scale instabilities in open pit mining create significant fall of ground hazards with potential for large runout distances of failed material. When such instabilities are identified, one possible geotechnical management approach is to use live radar monitoring of the slope to allow work to continue in the area until progressive deformation exceeds predetermined safe thresholds, at which point workers are withdrawn from the area until ‘controlled’ failure occurs. However, when the predicted failure and runout zones include a haul ramp or other critical infrastructure, failure prevention is often more economically favourable than accepting a ‘controlled’ failure. A common remediation approach for rotational slope instabilities is to add a resisting force to the toe of the slope, usually in the form of a buttress. The construction and scale of the buttress is determined by geotechnical modelling. This paper presents a case study of a toe-stabilisation buttress used to support an identified slope instability comprised of variable strength detrital materials at a Western Australia Iron Ore open pit mine. This case study covers the early detection of slope movement, subsequent geotechnical finite element analysis of the slope, buttress design and the execution strategy used to ensure a psychologically safe environment for operational personnel. The integrated solution is discussed, including the four-dimensional slope environment during progressive, transitional and regressive movement stages, as well as considerations for surface water management. Satellite InSAR, ground-based prism systems and ground-based radar systems were used, with real-time deformation alarming, 24/7 monitoring and a trigger action response plan in place. The geotechnical remediation has allowed continued productive movement in the pit. Batters underneath the buttress are currently being blasted and excavated under an approved geotechnical design, without reactivation of slope movement above alarm thresholds.

Keywords: slope monitoring, radar monitoring, operational safety, buttress

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