Economic significance of geotechnical uncertainties in open pit mines

Abstract

The major cost associated with open pit mine operations is waste stripping. While the steepening of slope angles reduces the stripping ratio, and hence operational costs, it also increases the likelihood of failure. Major slope failures incur significant cost elements including clean-up, disruption to mine operation, and damage to mining equipment and in some cases loss of reserves. Geotechnical engineers are often faced with the difficult task of finding the balance between slope optimisation and acceptable risk related to the likelihood of large slope failures. Technological advancements have allowed for the development of larger and deeper open pit operations, but have also created higher economic impact from potential slope failures. Given that the aim of mining operators is to maximise overall profits, it is surprising that most slope designs are based on deterministic design approaches, and limited attention is given to quantifying uncertainties in the geotechnical model. As most major decisions in the mining industry are made by senior management staff and financial staff, any attempt on linking slope stability analysis results with monetary values would improve the critical communication between geotechnical designers and decision-makers. Using Cowal Gold Mine as a case study, this paper illustrates economic risk caused by geotechnical uncertainties. The geotechnical risk estimate is generally subjective due to geotechnical engineers having to rely on limited data and engineering judgement. Geotechnical risk is compared against economic factors that are often perceived as important variables in mining operations.