Mechanisms of deterioration in a bored raise in brittle rock

Abstract

In this study, several wall deterioration mechanisms are identified for a 3 m diameter bored raise at a hard rock mine in Sudbury, Ontario, Canada, through taking high precision LiDAR scans, recording seismicity, and direct field observations in the raise. It is found that four factors influence the deterioration of the raise, which are stress change as the excavation is made, local geological structure, slashing-induced stress changes, and scouring of the raise as it was cut and as broken rock was dumped down the raise. It is also found that these multiple factors are often working simultaneously, leading to overbreak beyond the original bored dimension. The findings are useful for improving understanding of brittle rock failure, achieving a better understanding of the deterioration mechanisms for mechanical cut raises in hard rock, calibrating numerical models, and making better engineering decisions for ground support and precondition blasting to improve the health and safety for workers.