Observation of mining-induced faults in an intact rock mass at depth

Abstract

Stoping of a highly-stressed remnant in a deep South African gold mine was accompanied by considerable seismic activity and some significant rockbursts. The larger seismic events were registered some 60 km away at a World-wide Standard Seismograph Network (WSSN) station. Several shear ruptures were encountered subsequently in a tunnel driven to follow the mining faces. A careful study based on detailed exploration of two of these ruptures proved them to be the source of two of the larger rockbursts. The ruptures were essentially planar features of considerable areal extent with shear displacements of up to 100 mm of a normal dip–slip sense. Certain striking features were revealed by a scanning electron microscopic study of some of the fresh cataclastic rock-flour which formed part of the comminuted filling of these ruptures. These provided strong evidence for extremely violent fracturing phenomena in the faulting process. A proper understanding of these phenomena could provide useful insight into the source mechanism of rockbursts and the control of the accompanying damage. Because of the many similarities in morphology of the faults and in the nature of the seismic signals it could be argued that the rockburst rupture is a microcosm of the pristine earthquake. Understanding of the mechanics of the rockburst shear rupture might therefore have some relevance in the study of the earthquake source.