Potential for rock bursting and slabbing in deep caverns

Case histories reveal that slabbing and surface rock bursts in brittle rock may occur when ratios of the maximum tunnel-induced tangential stress and the small specimen unconfined compressive strength are as low as 0.35. A ratio of 0.5 results in low to moderate instances of bursting. Larger volume rock bursts associated with mine pillar failures do not appear to be common unless the ratio exceeds 1. The occurrence of surface bursts at ratios less than 1 is believed to result from the variation of field stresses within the rock mass and the reduction of intact strength with increasing specimen size, or scale effect. These findings were combined with finite element modeling of deep, multiple caverns to assess the potential for rock bursting during excavation.