Overmining Low Factor of Safety Coal Pillars using an Enchanced Monitoring System
DOI:
https://doi.org/10.17159/2411-9717/3756/2026Abstract
Prior to the Coalbrook Disaster in 1960, bord and pillar mining of the number two seam (S2) in the Witbank Coalfields often resulted in pillars with low factors of safety (FoS). At Goedehoop Colliery, S2 pillar stability was affected by top-and-bottom coaling, while at Greenside Colliery, stability was reduced by loading from a Mineral Residue Deposit (MRD). This compromised the stability of the S2 workings, impacting the mining of overlying number four seam (S4). To extend the life of mine, an alternative risk management approach using enhanced monitoring districts was implemented to safely mine the S4 reserves. This paper presents the use of geophone arrays to monitor micro-fracturing in S2 pillars and the interburden between S2 and S4, thereby enabling early detection of potential instability. Risk was assessed through fault and event tree analyses, determining acceptable failure probabilities. Automated seismic data processing distinguished micro-fracturing from noise, supported by extensive evacuation procedures for effective risk management. This facilitated the safe extraction of 4.70 Mt of S4 coal. The study quantifies the efficacy of geophone monitoring in optimizing coal recovery over low FoS pillars and assesses the application of van der Merwe’s (2019) time-based formulae for pillar stability analysis for this project.
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Copyright (c) 2026 Wynand Johannes van Wyk, Wikus Mahne, Graham Priest, Willem Liebenberg, Cornel du Toit
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