RISK-BASED SLOPE DESIGN: INSIGHTS FROM THE THABAZIMBI FAILURE
DOI:
https://doi.org/10.17159/Abstract
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 the 6th of 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 900m, 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, 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.
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Copyright (c) 2026 Marnus Bester, Thandile Dlokweni, Ian Basson, Corné Koegelenberg
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