Newcastle Chapter

Three Dimensional Boundary Element Analysis Of Stress At Lkab Mine, Kiruna, Sweden

Dr John Watson, Department of Mining Engineering, University of New South Wales

Mining of iron ore at Kiruna by sub-level caving is now at a depth of 500m below the surface, and stress related problems are being encountered. The purpose of the present investigation is to estimate the the stresses around the drawpoints from which fragmented ore is recovered. The rock may reasonably be taken to be isotropic and linearly elastic. The difficult aspects of the analysis are the need to carry out a mine-scale analysis to obtain results at a one metre scale, and the effect of error in determination of the pre-mining stress field.

Boundary elements of finite and infinite extent with quadratic variation of displacement are used. In a first analysis, the global redistribution of stress around the mine is computed. Results given by this analysis are then taken as input to a more detailed analysis of the part of the mine for which results are required at the one metre scale.

Preliminary results indicate that it may be possible to reduce the incidence of stress problems by careful attention to the sequencing of ore extraction. More definite conclusions cannot be drawn until uncertainties in the pre-mining stress field are resolved, probably by comparison of failures observed underground with those predicted by boundary element analysis rather than by further measurements of stress in the filed.

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