Review of Pillar Design and Cutting Practices in Geotechnically Challenging Ground Conditions

Sound pillar design and cutting practices maintain the integrity of mining operations. This paper evaluates pillar design and cutting practices in geotechnically poor ground conditions at one of the platinum mines along the Zimbabwean Great Dyke. Both numerical and empirical methods were used to analyse and improve the current system. The effects of overbreak together with pillar robbing have led to a decrease in safety factors of insitu pillars. Scaling of pillars and a decrease in actual safety factors gave an acute reflection that the current pillar design needs to be improved. The gathered results of regional pillars show that larger than design pillars were left to support potential fall zones resulting from persistent shallow north dipping structures. Pillar scaling was also influenced by the presence of geological structures. Undersized pillars and the existence of steeply dipping faults and sympathetic joints reduce pillar strength. The failed pillars are no longer contributing to the overall mine stability but provide local support due to the residual strength. New pillar design (7m by 4m) which takes into consideration the current structural data need to be implemented in a bid to improve safety. Staggering of pillars reduces the catastrophic consequences that may be spread over to the neighboring ends, hence causing pillar run. Numerical modelling softwares such as MAP3D and EXAMINE2D can be used for optimum pillar design as they show stress distributions as well as strength tension factors. The findings of this study can be adopted by other platinum mines within the same geological location since they are mining the same type of deposit using the same mining method.