Transitioning from mine operations to closure: the dilemma of differing geotechnical design acceptance criteria perspectives

Authors: Carter, TG; de Graaf, PJH; Dixon, J; Creighton, A; Macciotta, R; Silva-Tulla, F; Stacey, P

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DOI https://doi.org/10.36487/ACG_repo/2215_14

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Carter, TG, de Graaf, PJH, Dixon, J, Creighton, A, Macciotta, R, Silva-Tulla, F & Stacey, P 2022, 'Transitioning from mine operations to closure: the dilemma of differing geotechnical design acceptance criteria perspectives', in AB Fourie, M Tibbett & G Boggs (eds), Mine Closure 2022: Proceedings of the 15th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 237-258, https://doi.org/10.36487/ACG_repo/2215_14

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Abstract:
For open pit mining, understanding and managing slope performance is critical for both operations and closure. Towards the end of mine life, achieving reliability of slope performance in operations often necessitates real-time implementation of active slope stabilisation controls. This situation changes significantly towards closure, when production economics are no longer the priority, and resources for field monitoring control and active slope management diminish. The risk profile also shifts to a greater focus on stakeholder needs, including the environment and social acceptance, as land use changes. Although risk profiles will shift, the safety goal of ‘zero harm’ needs to continue to be achieved through all phases. Historically, most final pit slopes were not designed for closure. Rather, they tended to be optimised for production efficiency and thus were typically too steep for long-term reliability. The key question then becomes – what happens when the controls that have been put in place for maintaining their stability are decommissioned for closure? With sufficient understanding gained during operations, it may be possible to adequately forecast behaviour and define a Design Acceptance Criteria appropriate for the slope, for postclosure, once operational controls are decommissioned. This paper is hoped will help address this dichotomy and provides suggestions to meet industry objectives. It is also intended to promote discussion on this transition, such that industry and regulator perspectives can be accommodated alongside each other within the forthcoming Large Open Pit (LOP) Guidelines for Mine Closure handbook publication, currently in preparation under the auspices of the LOP initiative.

Keywords: design acceptance criteria, relative stability guideline, target stability reliability, geotechnical design, geotechnical risk, slope stability, as low as reasonably possible, post mining land use

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