203 Figure 8 - Location of cross-section for safety factors analysis 3.1. Safety factor distributions and evolution for the analysed pillar variants For the 4×4 m pillar scenario, the model indicates a generally “smooth” and spatially distributed roof-deflection process; however, the computed stability indices locally drop below SF = 1, which directly implies insufficient a non-acceptable stability margin for safe operation (Figure 9). Consequently, despite the favourable deformation character, this variant is rejected due to mechanical instability and collapse risk. Figure 9 - Safety factors distribution (excavation 4 × 4 m pillars) - left; and safety factor changes on the analyzed cross-section A-A’- right For the 8×8 m pillar scenario, the model predicts high SF values in the mining-front zone and in the area between the front and the liquidation line, reflecting strong short-term stability. Nevertheless, this geometry results in an overly stiff system during the early extraction stages; critically, once the operation advances into the liquidation zone—where remnant pillars are cut to the common post-critical size of 4×3 m—the model indicates a sudden and strongly localised loss of load-bearing capacity, associated with abrupt roof deflection (Figure 10). This behaviour is interpreted as unfavourable from a hazard perspective because it may promote dynamic cracking and potentially act as an impulse for higher-energy seismic events.
RkJQdWJsaXNoZXIy MTM0Mzk2