Li, J, Ferreira, JV & Le Lievre, T 2014, 'Transition from discontinuous to continuous paste filling at Cannington Mine', in Y Potvin & T Grice (eds), Proceedings of the Eleventh International Symposium on Mining with Backfill
, Australian Centre for Geomechanics, Perth, pp. 381-394, https://doi.org/10.36487/ACG_rep/1404_30_Li
Cannington Mine is an underground multi-metal mine that uses the sublevel open stoping mining method. The majority (>95%) of the void created by this mining method is filled with paste, a mixture of process tailings, cement and water. For each void to be filled all level openings are sealed with a fibrecrete fill wall. The cemented paste fill allows for a continuous retreating sequence between primary and secondary (or tertiary) stopes. Backfilling is an integral part of the mining cycle; consequently a reliable and productive paste fill system is required with integration between both surface infrastructure and the underground paste filling strategy.
To mitigate the risk of fill wall failure due to the pressure imposed on each fill wall by uncured paste fill a discontinuous filling strategy (or stop and cure process) was used at Cannington Mine. When the paste fill level in a stope was passing a level opening with a fill wall present, paste filling was stopped or slowed to allow the paste fill to cure. This discontinuous paste filling strategy caused 15-20% of paste fill downtime, each stop and cure usually involved changing to fill an alternate stope and required fill line flushing to clear paste from reticulation network after completion of and before starting up each fill run, and fill line changing.
A project was established in mid 2011 to investigate the effects of continuously paste filling behind a fill wall. The project involved numerical modelling of the strength of fibrecrete fill walls with various dimensions (width, height and thickness), correlated data gathered from in situ fill wall pressure monitoring, using pressure cells with varying vertical rate of rise, and different paste fill cement contents. The data analysis led to operational procedure updates allowing continuous paste filling and the establishment of a wall thickness design tool.
Project outcomes saw continuous filling behind both arched and flat fibrecrete fill walls, which resulted in a 15% reduction in paste fill down time; it allowed a reduction in fibrecrete fill wall thickness, which reduced fibrecrete consumption by 30% on average; and led to a reduction in paste fill line changes, which increased paste crew productivity, and decreased the frequency of cold joints caused by flushing in paste fill masses. A continuous paste fill strategy was successfully implemented and has been applied without incident since project completion in early 2012.
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