Since the commencement of mining at Tau Lekoa Mine in 1991, large wedge or dome collapses have been problematic. Crush pillars are used to prevent these and the current layout has been derived through iterative design. The span between crush pillars is based on an empirical relationship between the fallout thickness and span. Crush pillar spans are designed to limit the potential fallout height to a thickness that is controllable by means of internal support. The correlation between the span and fallout height is statistically poor and may mask underlying contributing factors. Observed thickness often deviate significantly from the design prediction and seem to cluster in certain areas. Geotechnical and mining data has been collected and statistical distributions have been determined to allow a probabilistic approach to the design of stable spans. A statistical analysis of eighty large collapses has also been conducted. Use of programs such as @RISK and J-Block have been made in assessing the risk associated with different spans and geotechnical conditions. Ultimately, the aim is to develop an optimised pillar layout that is beneficial from both a safety and economic perspective.
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