The development and application of destressing techniques in the mines of INCO Limited, Sudbury, Ontario

Rockbursts are the result of the sudden release of stored strain energy derived from the stresses induced by mining at depth or to a high extraction ratio. Control methods range from modifying geometries to altering the rock properties by destressing. The physical expression of the release of stored strain energy includes dog-earing, core disking, slabbing, pillar failure and bursting. A review of the historical development and a comprehensive list of the various methods of destressing are outlined. Special interest is paid to destressing of pillars, culminating in the description of the destressing of 25 Pillar, a regional pillar at INCO's Stobie Mine (world's largest destress blast to date). The destress slot, which was designed to promote failure in the core of the pillar, provides a slot along which mining can safely proceed. The risk of bursting has been reduced for the safely proceed. The risk of bursting has been reduced for the possible extraction of 1.8 million tons of ore between the 550 and 520-m levels.