Stability study for the footwall at Rana Gruber, Norway

摘要

The Rana Gruber is an iron mine in the North of Norway, 30 km east of Mo I Rana. The mine is located in a foliated gneiss host rock, and the ore body is about 70 m wide and more than 300 m deep. Due to steep dip and continuation at depth of the ore body, it is expected to reduce the mining cost by changing the mining technique to sub-level caving. Many underground works have been considered such as field tunnel, transport tunnels, drilling tunnels, shafts and etc. This paper presents a study to evaluate the stability of the footwall. It is because many infrastructures such as ventilation shaft, field drifts, the ramp, the crusher unit and the operational road can be affected from the footwall instability. However, this paper is focused only on the footwall stability in relation to the location of the operational road, which is located about 100 m from the mine edge. Different numerical models have been established in connection with site observations for reasonably predicting the development of fractured zone on the footwall corresponding to the mining progress. It is found that it may not be necessary to relocate the operational road. It is also recommended to use extensometers systematically installed to measure the displacement for verification and monitoring.