In Morwell Open Cut brown coal mine, the overburden 'firehole'
materials which have resulted from ancient coal fires vary-from hard
baked clays to firm laminated lacustrine clays. The need to pre-strip
designated areas to reduce the slope height and attain safe digging
conditions for the bucket wheel excavator operation is now accepted
practice at the open cut mine. In this study, the inherent spatial variability of undrained shear strength
of the clay materials has been incorporated in a visco plastic, finite
element based, probabilistic slope stability analysis. Data on the costs of
initial pre-stripping, excavation and slope failure are collected to provide
an economic basis for the optimisation of the design of the overburden
batters in Morwell Open Cut. This improved stability modelling is
enabling costly pre-stripping to be minimised while ensuring acceptable
slope stability conditions and minimising the risk to personnel and plant.