ROCK INSTABILITY AND RISK ANALYSES IN OPEN STOPE MINE DESIGN

Modern underground mining methods often call for the excavation of lar ge, often unsupported voids called stopes. In many cases, these are no nentry stopes, with the removal of broken rock (mucking) performed by remote control. With the risk to human safety thus reduced, stability concerns within the stopes are primarily driven by the economics of un planned overbreak and waste rock dilution of the mined ore. In this co ntext, it is appropriate to speak of acceptable risks of instability a nd to optimize design by balancing risk costs with productivity potent ial. Larger individual stopes generally increase productivity while re ducing stability. The modified stability graph is a popular empirical mine design tool that has been calibrated to provide discrete recommen dations for maximum stope dimensions based on a rock quality index. It seems appropriate to extend the method to account for variability in the calibration data and also for variability in each new set of input parameters. A risk template and associated probabilistic techniques a re proposed to supplement the discrete design limits currently establi shed.