Definition of the extraction-level layout, including geometry and dimensions of the excavations, is an essential aspect of the design of any block/panel caving operation. The design needs to guarantee that the excavations remain stable and perform as intended during the life of mine, in other words, prior, during and after caving production takes place, a span of time that frequently involves decades. The layout of these excavations involves an intricate network of drifts, access tunnels, drawbells and other excavations. A complex 3D mechanical numerical model that incorporates the extraction level, the undercutting level and the broken material surfaces and which simulates the progression of the undercutting advance and resulting caving propagation was developed. The purpose of the model is to assess the layouts, in terms of stress concentrations and plastic damage in pillars at the extraction level, particularly in the vicinity of the caving front. A method for geotechnical risk-based design under high stress conditions which uses tridimensional numerical modelling and probabilistic methods of analysis to determine the probability of pillar failure is described in this paper. The methodology included three main tasks: (1) evaluation of the factor of safety (FOS) and probability of failure (POF) representative of the stability conditions of the extraction level layout; (2) evaluation of the risk associated with economic losses resulting from impacts on equipment and on production; and (3) generation of a simplified geotechnical risk map to compare several mining years. The results of these analyses enabled the identification of risk mitigation options for those situations where acceptability criteria are exceeded.
