Study on the Fracture‐Orientation Effect of Hard Roof Breakage Characteristics in Karst Mine Mining

ABSTRACT Southwest China commonly faces the complex challenge of coal seam mining within densely karstified regions. Taking Guizhou's Yudai Coal Mine as the study context, this paper employs theoretical analysis, numerical simulation, and physical experiments to investigate the failure mechanisms of karst cavities post‐mining, the migration mechanisms of overlying rock fractures, and stress distribution patterns within karst environments. Through analysis, the critical stress conditions for cave collapse were determined. By configuring caves of varying shapes and hard rock layers of different thicknesses, it was found that circular caves exhibited the highest stability, followed by irregular caves, with square caves demonstrating the poorest stability. The thinner the hard rock layer, the greater the disturbance to the karst cavities and overlying rock, resulting in increased subsidence of the overlying rock. The fissures generated by the instability of karst cavities within fracture zones exert a certain guiding and attracting effect on mining‐induced fractures, while also exerting a certain hindering effect on mining impacts. Following the fracturing of the overlying strata, the periodic pressure step distance exhibits a marked increase upon reaching the karst cavities, causing post‐mining displacement and strain of the overburden to concentrate at the karst cavities and the left‐hand goaf. Therefore, mining operations conducted beneath hard roof strata in karst mining areas can implement reinforced support measures for the hard roof overlying karst cavities. This prevents stress concentration caused by cavern collapse. The findings of this research may provide valuable reference for the safe extraction of coal seams in karst environments.