Long-term stability analysis of open pit mine slopes : a case study of Wearne mines in Limpopo

Abstract

The main objective of the study was to conduct a long-term stability analysis of the slope, which due to blasting and continuous mining activity may deteriorate in its strength and since there is very little slope stability monitoring done, the analysis is warranted. Several methods were applied to achieve the objectives. These methods include Kinematic analysis, Limit equilibrium and Numerical modelling. The kinematic analysis method made use of the discontinuity orientation and the slope orientation to determine the probability of different types of failures occurring. These failures include planar, wedge and toppling. Limit equilibrium method was used to determine the Factor of safety (FoS) of the slope by analysing the driving forces and the resisting forces of the slope. OPTUM G2 which is a numerical method was then used to simulate the failure of the slope in the presence of different length or depths of discontinuities. Lastly the ROCFALL which is also a numerical model was also used to determine the extent at which the rock will travel down the slope in case of failure. The results produced by the kinematic analysis showed that the slopes are most likely to experience toppling failure more than planar and wedge failures. The Limit equilibrium results on the other hand showed that the slopes were stable based on its FoS value. OPTUM G2 proved that the increase in the length of discontinuities reduces the strength of the slope. Lastly, the ROCFALL models showed that the slopes geometries are well on balance and the presence of safety berms will prevent the rock rolling to the lower benches.