SUMMARY:

The chances of reducing the rockburst hazard in mining will be improved once the essential mechanism of the phenomenon is understood. In the deep gold mines of the Central Witwatersrand, the problem has been resolved to some extent; the nature of fractures which cause rockbursts has been clearly established. In the course of pining a large isolated remnant at a depth of 200m below surface, 15 rockbursts occurred over a period of four years with magnitudes, ML, ranging from 1, 7 to 3, 4. In a tunnel subsequently developed about 20m below the mined-out area, the traces of more than 20 burst fractures were revealed and one of these was explored in detail some four years after its origin. The similarities between these man-made fault zones and the crustal faulting of shallow earthquakes is sufficiently marked to suggest that Reid''s concept of an elastic rebound mechanism might explain the intense damage that sometimes results from such events.

1. INTRODUCTION

Because a rockburst in a deep, hard-rock mine is essentially a violent and transient phenomenon, its origin and tend to be obscure. Any chance in the rockmass that may precede unstable failure has no visible or audible effect and the damage caused by the rockburst usually obliterates any after-effects which could yield evidence of its cause. Traces of intensely comminuted fractures are revealed by further enlargement of the stopes or by subsequent development of tunnels in its vicinity. The circumstantial association of these burst fractures with the rockburst process has been noted by Cock et al (1966) and Pretorius (1966). In particular magnitude frequency relationship, the location with, respect to the mine workings and the association between the source of the energy and the deformation of the rock mass have been satisfactorily established-McGarr (1976), McGarr and Wiebols (1977).

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