An investigation of Westonaria formation lavas (WAF) and it's influence on the rock engineering design at Goldfield's No.4 (Ya Rona) shaft pillar extraction

Durapraj, Shyandra
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Geological complexity has always been a large contributor to instabilities at the mines on the Far West Rand. Part of the problem lies in the unknown nature of many of the rock types and formations that overlie or underlie the conglomerate reef bands within the rockmass. One of these little known rock types is the highly altered Westonaria Formation Lavas (WAF), which has impacted significantly on the stability, production sustainability and the rock engineering designs at many of the mines in the area. The Ya Rona Shaft Pillar Extraction is one of the mining operations where WAF has determined the course of many interventions. Failure of the WAF has occurred at mines that had not identified it as a potential hazard, which has led to large-scale fall-outs, significant damage to excavations, particularly shafts, and more importantly, operational downtime. Under this risk profile, Ya Rona shaft would not be able to sustain a profitable production profile should failure of the WAF occur. This research report investigates the WAF rock type, why it poses such a threat to stability, and how it influences rock engineering design where it is encountered. Using the available literature, rockmass rating systems and numerical modelling of the Ya Rona Shaft Pillar Extraction, classification of WAF will be attempted. Moreover, the research report will show what mitigation measures may be required to achieve stability under the WAF conditions, and also provide a guideline for rock engineering design under WAF conditions within a shaft pillar extraction.