Authors: Saunders, E; Yoon, A; Cernik, E; Martin, M

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Saunders, E, Yoon, A, Cernik, E & Martin, M 2023, 'Review of historical and new monitoring data for geotechnical subsidence assessment at San Manuel and Kalamazoo block cave mines', in B Abbasi, J Parshley, A Fourie & M Tibbett (eds), Mine Closure 2023: Proceedings of the 16th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth,

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San Manuel and Kalamazoo historical mine operations have been formally closed since 2003 with significant efforts to decommission infrastructure and establish long-term landforms, along with other key activities. The adjacent mining units are located in Arizona, United States. Monitoring and ground control management of the open pit and surface above the former block caves is a continued mandate of the closure asset team for regulatory compliance. During and following mining, observable subsidence features have formed and radiated around the underground footprints. The geometry of these features has been defined by the underlying geology and rock mass conditions, block cave progression and the excavation of an open pit through earlier subsidence at San Manuel. In recent times displacement may not be observable to visual inspection but can be detected by some monitoring techniques. This paper presents a case study evaluation of the subsidence features and their possible long-term behaviour using historical and new monitoring data. The study highlights the appreciable gaps in the geotechnical data and monitoring record, and the attempts to maximize understanding through publicly available aerial imagery. Important data sources (i.e., development plans, crack mapping) and monitoring techniques (i.e., drone surveys, InSAR) are each examined with regards to the required precision, limitation, and the actual value to this evaluation. The datasets were further evaluated to understand post-operation subsidence to verify where the bulk of the displacement has already occurred. The consolidated findings were compared against conceptual block cave behaviour established in industry and empirical break-break relationships.

Keywords: open pit, caving, subsidence, geotechnical, stability

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