Method for determining the width of protective coal pillar in the pre-driven longwall recovery room considering main roof failure form

A pre-driven double recovery room is widely used to safely remove longwall equipment in longwall coal mining. The stability of protective coal pillars is a crucial factor influencing surrounding rock deformation and failure in the pre-driven double recovery room. It is significant to characterize the loading mechanisms of protective coal pillars subjected to front abutment pressures to meet the enhanced design. In this study, surrounding rock deformation and protective coal pillar stress analysis of the recovery room are investigated through two case studies presented in the 15205 and 15206 panels of 5(-2) coal seam at the Hongliulin Coal Mine in Shaanxi Province, China. It was observed that the surrounding rock deformation and protective coal pillar stress of the recovery room is quite different from adjacent panels of the same coal seam. It was also observed that the roof-to-floor convergence of the recovery room in the 15206 panel is 30% less comparison with 15205 panel and the increase in the protective coal pillar stress in the 15206 panel is 50% less comparison with 15205 panel. Further, the periodic weighting data and the failure form of the main roof have been analyzed after establishing an evaluation model for load estimation and derivation of the formula for evaluating the width of the protective coal pillar. It was noticed that the main roof break position has a significant impact on the width of protective coal pillars. It was also noticed that the critical width of the protective coal pillar in the recovery room of 5(-2) coal seam is 23.8 m. The optimized protective coal pillar width is obtained applied in both the 15207 and 15208 panels and found that the stability of surrounding rock of the recovery rooms is ensured.