The spatial, temporal and energy related aspects of fracturing ahead of a-gold mine stope at a depth of 2160 m are described with reference to microseismic activity monitored by a small-scale array of accelerometers. The indicated location, extent and orientation of fractures ahead of the advancing stope correlated well with a numerical analysis based on Excess Shear Stress. Changes in the nature of fracturing during the remnant stage of mining are described, and are discussed with reference to the increased amount of energy released by mining at this stage. A correlation between the Gutenberg and Richter b-valuea of microand macro seismic data and the fractal dimensions of the source region is confirmed, and provides useful information regarding the source dimensions and mechanisms of seismic activity.
Les aspects spatiaux, temporaux et lies à l'energie de la formation des fissures en avant d'un gradin d'une mine d'or à une profondeur de 2 160 m sont decrita en tenant compte de l'activite microsismique controlee par un deploiement peu etendu d'accelerometres. L'emplacement indique, l'etendu et l'orientation des fractures en avant du gradin avancant ont bien correspondu à une analyae numerique basee aur extrème contrainte de cisaillement. Lea changements dans la nature de la formation dea fiasures pendant la phase remnante des operations minières sont decrits et sont discutes en tenant compte de la quantite augmentee de l'energie degagee au cours des operstions minières à cette phase. Une correlation entre les b-valeurs de Gutenberg et de Richter des points microsismiques et mecrosismiques et les dimensions ‘fractsl’ de ls region d'origine est confirmee, et a fourni d'information utile en cs qui concerne les dimensions d'origine et les mecanismes de l'activite sismique.
Die raumlichen, zeitlichen und energiebezogenen Aspekte der Bruchbildung im Vorfeld eines 2 160 m tiefen Abbauortes in einer Goldmine werden beschrieben hinsichtlich der mikroseismischen Aktivitat, die von einer beschrankten Anordnung von Beschleunigungsmessern ueberwacht wird. Die so bestimmten Werte fuer Lage, Umfang und Orientierung von Bruechen im Vorfeld eines vordringenden Abbauortes standen in guter Wechselbeziehung mit einer numerischen Analyse, welche die ueberschussige Scherspannung zur Grundlage hatte. Veranderungen in der Art und Weise der Bruchbildung wahrend der Schlussphsse des Abbaus werden beschrieben, und werden in Bezug auf den Anstieg der durch den Abbau in dieser Phase freigesetzten Energie diskutiert. Eine Wechselbeziehung zwischen den von Gutenberg and Richter bestimmten b-Werten fuer mikro- und - makroseismische Daten einerssits, und den fraktsldimensionen des Ursprungsortes andererseits, findet Beatatigung, und lieferte nuetzliche Information ueber die Dimensionen des Ursprungsortes und ueber Mechanismen seismischer Aktivitat.
A complete understanding of the fracture and deformation processes occurring in the vicinity of the deep gold mine stopes of South Africa is essential for the safe and efficient extraction of these gold bearing strata. The behaviour of the-rock mass in this region has important implications for stope layout and support design, for developing mechanized mining methods, for determining why rock ahead of the face fails in an unstable manner, occasionally resulting in rockbursta and, most importantly, for the safety of the many people who work at the stope face.
The pattern of fracturing occurring ahead of the. stope face as the high mining induced stresses exceed the strength of the surrounding intact rock mass has been studied for a number of years (McGarr 1971, Roering 1978, Legge 1985 and Brummer and Rorke 1984). To gain a greater overall understanding of these processes of fracture and deformation, a cuboid microseismic network of 25 m side was installed symmetrically about the reef horizon ahead of an advancing stope face.As the stope face moved through the network many thousands of microseismic events were captured and recorded, yielding information concerning the temporal and spatial distribution of fracturing, and the energy content and frequency of occurrence of microseismic emissions accompanying the fracturing.
A great deal of seismic research has been conducted on the South African goldfields, and has involved the use of macro-, mini-, and microseismic networks, spanning seismic events with local magnitudes ranging from -4 to +5. Hicroseismic studies have included those by Brink and O'Connor (1983) on rockburst prediction, and by Pattrick (1984) who designed the system used in this study and applied it in an earlier experiment.
The microseismic network was installed on a gold mine which is situated in the Klerksdorp district some 160 km from Johannesburg. The reef being mined at this site was the Vaal Reef which, stratigraphically, lies near the middle of the Central Rand Group quartzites. The Vaal Reef is a tabular, laterally extensive gold-bearing conglomerate, which in this region of the mine is about 1,1 m wide and dips at 8° to the west.
