By T. Dlokweni, M. Bester, C. Koegelenberg, I. Basson
Certain degrees of safety, economic, and financial risk are implicit in any mining operation. At Thabazimbi Mine, slope stability was one of the major sources of risk, largely due to data uncertainties. Consequently, a risk-based approach in slope design was followed.
On 6 June 2015, a slope failure occurred in Thabazimbi Mine’s Kumba pit, involving approximately 65 million tonnes of rock failing into the pit and the valley below. Although the failed mass moved rapidly and resulted in a run-out distance of approximately 900 m, controls
had been put in place to successfully evacuate all personnel. Risk assessment during the onset of
failure supported the decision to not compromise the safety of personnel in any way, leading to
unavoidable equipment loss. This contribution presents the failure as a case study in the context of a risk-based approach to slope design as well as the importance of implementing geotechnical controls to effectively manage slope instability risk. Furthermore, a comprehensive back-analysis was performed,
on a fully constrained 3D model, utilising 3DEC software, to gain insights into the failure
mechanism. In conclusion, lessons from the Thabazimbi slope failure are valuable as they demonstrate the importance of following a risk-based approach in slope design to effectively manage safety
and financial risk in open pit mines.
Risk-based slope design: Insights from the Thabazimbi failure