Rock mass response to mining induced over-stresses in a sub-level-caving operation, case study at the Kiruna Mine, Sweden

2001

Emmanuel Henry, Michel Plouffe, Martin Côté, Daniel Sandström,

The Kiruna Mine, operated by Luossavaara-Kiirunavaara AB (LKAB), is a large-scale sublevel caving operation located in the Arctic Sweden. Iron ore is extracted at a rate of 60 000 tpd from a four-kilometre long, 80 to 100 m thick and 60 degree dipping orebody. Actual production depth is 800 m under the top of the footwall and about 550 m under the average regional ground level. Because no support is left between the footwall and the hangingwall and despite the relatively low mining depth, extraction results in the formation of a huge stress shield that modifies the original stress field and concentrates it just beneath the mining level. Effects of stress concentrations on the rock mass are monitored through field observations and a seismic system. Severe stress-induced deterioration of openings is visible to a certain radial distance from the mining level: pillar crushing and fault slips are more and more common and extended. The seismic system, installed in collaboration with CANMET, confirms the field observations and completes them in the rock mass: fault slips and major seismic events are recorded. The system proves its effectiveness to outline the extension of the dynamic response of the rock mass, which actually seems much larger than field observations let think.

Keywords: Seismic monitoring, Pillar crushing, Fault slip mechanism, Stress shield, Numerical modelling, Sub-level-caving