Optimizing Stope Panel Spans at an Eastern Bushveld Platinum Mine by Probabilistic Analysis

Geotechnical data can be used to optimize the support design for a specific geotechnical environment. The current legislative environment in South African mining drives rock engineers to design support layouts which attempt to engineer out situations of noncompliances, therefore possibilities to optimize support designs are limited. The modelling of optimized support designs can nevertheless be used to substantiate the current support designs and mine layouts. A study was recently conducted to optimize the stoping panel lengths at a platinum mine in the Eastern Bushveld. The mine extracts the shallow-dipping UG2 chromitite seam at depths ranging from 30 to 400 metres below surface, using labour-intensive narrow-reef stoping. Geotechnical data was collected using scanline mapping, after which the data was processed and analysed. This allowed the authors to define the mine's geotechnical environment in terms of the joint set orientations and characteristics, as well as the likely key block shapes and sizes. A probabilistic analysis was used to compare a range of mining layouts, panel spans and support designs for the defined geotechnical environment. Within the application, a database of synthetic key blocks was created based on the joint set orientations and characteristics. This was calibrated against the mine's actual fall of ground database. The number, volume and failure mechanism of likely falls of ground were then generated for alternative scenarios, using a common synthetic key block database. The results of the individual analyses were then analysed and a hazard profile was produced for each option, based on the block size distribution. Finally, the different hazard profiles were benchmarked against the hazard profile of the current mining layout and support system, providing the mine's management team with sufficient information to make a decision regarding changes.