VIOLENT FAILURE OF A REMNANT IN A DEEP SOUTH-AFRICAN GOLD MINE

The violent failure of a peninsular remnant at a depth of 2300 m below surface occurred in a mine in the Carletonville Goldfield of South Af rica, severely damaging a stope mining the Ventersdorp Contact Reef (V CR). At the rockburst site the VCR is 1-2 m thick with a lava hangingw all and quartzite/conglomerate footwall. The remnant had been formed a s the result of a fault and 'roll' encountered during mining. Observat ions at the rockburst site led us to conclude that the seismic event, with local magnitude of 2.1, resulted from failure of the remnant with attendant movement into the workings. The event could not be explaine d by a single shear slip. Two different damage mechanisms were identif ied. Firstly, the face and footwall on the east side of the remnant we re violently ejected into the void between the original face and first line of timber packs following failure and dilation of the remnant an d its foundation. Secondly, the hangingwall on the south side of the r emnant fragmented and collapsed when subjected to intense seismic shak ing. This response was due to the presence of a bedding-parallel fault and calcite-coated joints in the vicinity of a 'roll'. The stope supp ort system failed to contain the seismically fragmented rock. (C) 1998 Elsevier Science B.V. All rights reserved.