Optimization of Crown Pillar Thickness in the Stress Relaxation Zone Surrounding Sub-Level Open Stopes

The excavation of steeply dipping ore deposits using sub-level mining techniques with delayed backfill can cause stress relaxation and concentration in the stope hanging wall and footwall at deeper depths. Designing adequate crown pillars that can withstand significant horizontal stress and prevent the collapse of the hanging wall and footwall is crucial for ensuring safe mining operations. This study developed a methodology for predicting the appropriate crown pillar thickness for depths between 510 and 1000 m based on 240 non-linear numerical models with Mohr–coulomb elastoplastic failure criteria under plane strain conditions with five parameters affecting crown pillar stability. A precise and reliable empirical equation has been devised to compute the safety factor (SF) of the crown pillar. The equation has a high predictive capability with an R² value of 0.85. Design charts were developed for various geo-mining conditions and working depths to estimate the optimal crown pillar thickness.