Abstract: To address the instability issues associated with coal pillar spalling in thick sandstone roof strata under high mining heights,this study focuses on the control of coal pillar spalling in the 20113 return airway of the Yushuwang Mine as a case study. The characteristics of spalling failure and the primary influencing factors are analyzed. A quantitative characterization method for fracture degree based on the fractal dimension of borehole fractures,using MATLAB image processing technology,is presented. The evolution of the surrounding rock displacement field under four different optimized support schemes is comparatively simulated. A coal pillar spalling control method,centered on " strong roof control,high-resistance rib protection, and inclined I-beam + anchor net coupling control," is proposed and implemented through industrial field tests. The research findings indicate that:① The primary characteristics of coal pillar spalling include diverse failure modes (high-rib wedge spalling + mid-section rib bulging + S-shaped),extensive failure depth,and severe support anchorage failure. ② The superposition effect of thick sandstone strata,low coal strength,abnormal mine pressure manifestation,and significant pillar compression rod effect are the dominant factors inducing coal pillar spalling. ③ The combined support technology of " hydraulic support working resistance enhancement + anchor net cable + anchor cable I-beam" is the optimal support scheme. After adopting this scheme, the convergence of the roadway roof,floor,and ribs were only 143 mm and 181 mm,respectively,representing reductions of 70% and 72% compared to the original support scheme. The loosened zone ranged from 0. 524 m to 0. 613 m,with no significant cracking on the coal pillar surface,and a substantial improvement in the integrity of the anchored coal body. The support effect was favorable,effectively resolving the instability issues of coal pillar spalling in thick sandstone roof strata under high mining heights. 

Key words: thick sandstone group,coal pillar slope,fractal dimension,numerical simulation,support optimization