Analysis of progressive failure of a mine slope in a Western Australian open-pit gold mine

Development of time-dependent rock mass strength and deformation models is a strategic research direction of CSIRO Exploration gr Mining. A component of this research is the numerical modelling of mine slopes with a history of time-dependent failure. During 1990, approximately two years after excavation, a slope in the Eureka open-pit gold mine in Western Australia failed on three occasions. The failures were analysed using a finite difference code with Mohr-Coulomb and ubiquitous-joint models, and excavation of the mine was simulated in four stages. The numerical results show that the failures each started as a local yield region near the prevailing toe of the slope, and this yield region propagated upwards due to strength deterioration of the rock mass. Steeply dipping, pervasive foliation played an important role and formed approximately one third of the failure surface. The strength deterioration may have resulted from softening due to water adsorption and through local yield and propagation of defects.