A risk-based methodology for establishing landslide exclusion zones in operating open pit mines

The high consequences of recent large open pit slope failures have increased industry and regulatory interest in establishing exclusion zones beneath an impending pit wall failure. This paper proposes a methodology to delineate an exclusion zone for an impending pit slope failure. The focus of this paper is a framework for the management of life loss risk to the most exposed individual. The probability of the landslide occurring and the probability of the resulting landslide being very or extremely rapid are described in this paper. Set in a probabilistic framework, empirical runout analysis tools are useful for estimating the spatial probability of impact throughout the open pit and establishing exclusion zones. Runout exceedance probability charts calibrated to a large dataset of pit slope failures are provided. The temporal probability that the most exposed individual is present and cannot be evacuated is also described. The resulting risk is mapped across the pit floor by dividing it into square grid cells and calculating the probability of death to the most exposed individual for each cell. The cells can be colour coded to indicate specific risk exposure ranges relative to the exclusion zone set. A conceptual case study is used to illustrate the proposed methods.