Authors: Karlsson, M; Ihanus, J; Matinlassi, M; Nikkinen, T

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Karlsson, M, Ihanus, J, Matinlassi, M & Nikkinen, T 2022, 'Geotechnical challenges driving the mining method change: transition from sublevel stoping to sublevel caving', in Y Potvin (ed.), Caving 2022: Proceedings of the Fifth International Conference on Block and Sublevel Caving, Australian Centre for Geomechanics, Perth, pp. 713-724,

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Kemi Mine is the largest underground mine in Finland with annual ore production of 2.7 Mt. The mine started as an open pit in 1968 and transitioned to underground mining in 2006. Underground mining started with sublevel stoping (SLS) from 500 level (metres below surface). Current mining is challenging due to geotechnical conditions that affect the stope size and tunnel stability. As mining proceeds deeper in depth, the conditions are anticipated to be more difficult than on the upper levels, thus a change in mining method is required. Historically squeezing ground is the principal mechanism that damages the rock mass in the production area (slow displacement of backs and walls inwards) notwithstanding stope collapses due to the exposure of wedges. Increasing geotechnical difficulties result in a reduction stope, dimensions causing sub-optimal and complex production scheduling. These issues led to a process where alternative mining methods were evaluated to replace SLS and increase ore recovery and production reliability. Sublevel caving (SLC) was shortlisted as one potential alternative and led to a series of studies, evaluations and finally to a limited scale trial mining. The introduction of a new mining method within an operating mine is a huge challenge. During pre-trial and trials the execution team established a number of new routines to mitigate the issues. These included, among others, planned information events for all mine personnel, development of new operating procedures specifically for SLC, and a large number of internal workshops with key personnel involved in the geology, mine planning, operations and support services. This paper presents the background, settings and selection criteria for a SLC mining method at Kemi Mine along with the challenges encountered and steps taken in the change management process.

Keywords: sublevel caving, transition, deep mine, change management

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