Destress blasting or preconditioning, a rockburst control measure, has been tried to control strainbursts since the beginning of the 20th century. The concept of destress blasting evolved from the observation that the zone of highly fractured rock immediately surrounding some deep underground openings seems to offer some shielding to both the occurrence of and damage from rockbursts. It was argued that extending and maintaining this zone of the fractured rock ahead of a face can reduce both the occurrence and effects of rockbursts. Destress blasting was again re-evaluated for South African gold mines in the late 1980s. The current practice in South Africa has notable departures from the original concepts of destress blasting with the main objective of destress blasting being to activate already existing fractures rather than initiate new ones, and locating the blastholes in zones that are already fractured. Also, the position and depth of destress blast-holes should be confined to the already fractured zone for an effective application. The aim of destress blasting is to In North America, destress blasting is more widely practised, particularly on sill and crown pillars in deep, narrow-vein mines. The following summarize the prevalent notions for destress blasting particularly applied to pillars and stopes of the steeply dipping veins of metal mines in North America.
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