Recent case histories of the application of the empirical destressability index methodology

The destressability index methodology for the assessment of the likelihood of success of large-scale confined destress blasts in underground mine pillars was developed empirically, based on documented case studies in hard rock mines. Since its introduction it has been successfully employed to design such blasts at several seismically active mines. This article presents two recent case histories of the application of this methodology. The first case study was at the Fraser Copper Mine in the Sudbury Basin, where a choked destress blast was detonated to stress-shadow a seismically active cut-and-fill mining horizon. Vibrating wire stress cell data were recorded over a period of two years after the blast, which shed some light on the stress remobilisation process that followed this choked destress blast. The second case study was at the Onaping Mine, also in the Sudbury Basin, where a deep seismically active remnant waste pillar was targeted.