Regular fracturing of hard rock around deep level stopes enables mechanical rock breaking to be an effective alternative to standard drilling and blasting. Numerical modelling of the failure processes around highly stressed, advancing stopes shows that an initial pattern of regularly distributed failure is followed by the onset and development of localized bands of shear failure in which additional inelastic deformations are concentrated. The further development of a regular fracture pattern is subsequently reduced or even inhibited to such an extent that areas of, unfractured rock ("hard patches"), which reduce the effectiveness of any mechanical rock breaking method drastically, may be encountered. The mechanisms identified from the numerical analyses indicate mining strategies which can be used to prevent the development of, localized failure.
L"occurr.nce systematique de fractures autour des excavations minières à grande profondeur fait de la destruction mecanique de roches une alternative valable vis-à-vis à la methode classique d"explosives. Des simulation. numeriques de mecanismes de rupture autour de tailles ont indique que l"occurrence initiale de fractures systematiques est suivie par l"occurrence de zone de fractures de glissement, caracterisees par la deformation supplementaire non-elastique. La probabilite d"avoir une fracturation regulière et systematique est donc diminuee et peut même être nulle, si des zones de roches intactes et dures sont presentes. Ceci diminue la possibilite d"appliquer effectivement la destruction mecanique de roches. Les simulations numeriques ont indique des strategies minières, qui peuvent être appliquee pour eliminer des fractures locales.
Regelmassige Bruchbildung in Hartgestein in tiefen Grubenbauen ermöglichen eine mechanisierte Gewinnung als effektive Alternative zum herkömmlichen Bohren und Sprengen. Numerische Modelle des Bruchvorganges in hochgespannten, fortschreitenden Abbauen zeigen, dass ein urspruenglich vorhandenes Muster von regelmmassig auftretenden Bruechen gefolgt wird von Enstehung und Entwicklung örtlich begrenzter Bandern von Scherbruechen wozu sich zusatzlich inelastische Verformungen konzentrieren. Eine weitere Entwicklung von regelmassigen Bruchstrukturen wird folglich verringert oder sogar gehemmt bis zu einem solchen Ausmass, dass Gebiete unzerbrochenen Gesteins ("harte Stellen") entstehen können; diese reduzieren die Effektivitat einer mechanisierten Gesteinszerstörung drastisch. Die aus den numerischen Analysen abgeleiteten Mechanismen zeigen mögliche Abbaustrategien, die benutzt werden können, um die Entwicklung von lokalen Bruchvorgangen zu verhindern.
Inelastic deformations and. tress distributions around deep level stopes result in problems such as rockbursts and excessive closures, which are areas of great uncertainty to the South African gold mining industry. Although it is generally accepted that some basic mechanisms control the inelastic deformations and stress distributions, th.se mechanisms are still not fully understood and have not been described or modelled satisfactorily.
Previous research in this respect has concentrated mainly on underground measurements and observations of deformation. and strain changes around excavations and has provided a wealth of data. Interpretation and analysis of such data has been reported by many of the researchers involved (Legge, Herrmann, Jager, Brummer etc). Brummer (1987) even proposed basic deformation mechanisms.
he identification of mechanisms based on field data is, in the deep level gold mining context, a cumbersome task for two reasons:
firstly, many factors which influence the data can not be assessed properly and therefore affect the data in a random and unquantifiable manner,
secondly, the chronology of fracture formation is difficult to interpret as the exposures of fractures are often records of individual fractures and superimposed on one another before exposure. (Brummer, 1987).
