Understanding rock mass–backfill interaction in support of deep and high-stress mining

Authors: Grabinsky, MW; Thompson, B; Jafari, M; Counter, DB; Bawden, WF Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2465_89

Cite As:
Grabinsky, MW, Thompson, B, Jafari, M, Counter, DB & Bawden, WF 2024, 'Understanding rock mass–backfill interaction in support of deep and high-stress mining', in P Andrieux & D Cumming-Potvin (eds), Deep Mining 2024: Proceedings of the 10th International Conference on Deep and High Stress Mining, Australian Centre for Geomechanics, Perth, pp. 1349-1364, https://doi.org/10.36487/ACG_repo/2465_89



Abstract:
There is currently a need for better understanding of backfill design requirements at depth or under highstress conditions, or in rock mass with poor quality. It is generally acknowledged that rock mass closure affects backfill performance but there is currently negligible practical guidance for a design engineer. Understanding how mining conditions induce closure onto backfill is essential, as is predicting the reaction of the backfill to passively supporting the rock mass. This paper introduces a new framework for backfill design incorporating closure conditions. Rock mass-backfill interaction is considered using parametric studies that consider the backfill’s ‘loading system’ as a combination of field stress, rock mass stiffness and the evolving geometry associated with ongoing mining. Parameterisation is used so that the extent of potential rock mass closure can be estimated for different mining conditions. Then, stiffness contrasts between backfill and the rock mass are considered. Load transfer from rock mass to backfill must be understood, neglecting initial closure occurring before the open stope is backfilled. The resulting analysis framework predicts the extent to which backfill distress may be an issue and enables assessment of the efficiency of increasing backfill strength and stiffness for a particular design scenario. A critical determination is that opportunities to engineer the backfill’s strength and stiffness to resist initial rock mass closure on the backfill when the adjacent stope is mined is limited to cases where stresses are relatively low and rock mass quality (evaluated using the geological strength index [GSI] or equivalent) is moderate to high. Conversely, in high-stress conditions the initial closure on the backfill may have negligible consequences if the rock mass quality is sufficiently high. These extremes are quantified for a particular mining method and geometry. However, the analysis approach is equally applicable to other mining methods and geometries, and the framework to tackle these different mining problems is provided.

Keywords: rock mass closure, backfill, evaluating backfill efficiency in supporting rock mass

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