Back analysis of subsidence above old open stopes in an Indian hard rock mine by numerical simulation

Occurrence of surface subsidence above old, shallow open stopes in Badia Section of Mosaboni Copper Mine was noticed in October/November, 1994. As mining in this patch was completed more than 25 years ago, no correct information could be gathered regarding the latest topography of the area and it could not be inferred really how much ground movement took place here because of this subsidence. To find out an answer to this question, a Boundary Element Model study of this subsidence was carried out simulating progressive failure in rock mass. Comparison of the findings of the simulation results with the field observations indicated the model to be realistic and acceptable. Thus the magnitude of maximum subsidence was estimated to be about 0.46 m and a methodology was worked out to evaluate subsidence proneness of the ground above other shallow open stoping areas in this mine. The problem, the approach, the exercise and the findings has been discussed in this paper.