Evolution characteristics of overlying strata in inclined thick coal seam fully-mechanized mining faces passing abandoned roadway and comparative experimental study on different backfilling control methods

In inclined thick coal seam fully mechanized caving mining faces, the passage through abandoned roadways exhibits more frequent strata movement and ground pressure manifestations compared to horizontal coal seams due to inclination effects, with significantly exacerbated challenges including rib spalling, roof collapse, and pressurizing of hydraulic support. Taking the 1213-1 fully mechanized caving face in Nancha Coal Mine as an engineering case for roadway crossing operations, this research systematically combines theoretical modeling, mechanical computation, numerical simulation, and industrial experimentation to elucidate the failure mechanisms and stress-strain characteristics of surrounding rock masses in steeply dipping thick coal seams during abandoned roadway crossings, with comparative analysis of control efficiencies between wooden cribbing support scheme and super-high water material backfill scheme. The results demonstrate: ① Through establishing 2 mechanical models analyzing shield load interactions with main roof weighting effects and main roof bending moments at different face-roadway positions, combined with 3D numerical modeling of the 1213-1 face crossing operation, it was revealed that the critical factors controlling surrounding rock failure are the coal pillar width between working face and abandoned roadway along with roadway inclination. Vertical stress redistribution intensifies progressively along the face dip direction during mining advancement, showing reduced stress variation magnitude in areas farther from the abandoned roadway under mining disturbance. However, when the caving face approaches the abandoned roadway, vertical stress fluctuations become significantly amplified, inducing stress concentration phenomena that trigger substantial rock mass deformation. ② FLAC^3D numerical simulations indicate that super-high water material backfill significantly enhances the composite strength of surrounding rock in abandoned roadways, effectively mitigates stress concentration within roadway zones, and substantially reduces roof deformation magnitudes. Conversely, wooden cribbing support demonstrates limited effectiveness, showing minimal differences in vertical stress distribution and deformation patterns compared to unsupported roadway conditions. ③ Field trial comparisons demonstrate that wooden cribbing support scheme yield poor support performance characterized by severe roadway deformation, with structural collapse occurring in high-inclination zones and subsequent roof material leakage. In contrast, ultra-high water material filling provides dense roof support, enhances roadway surrounding rock integrity, effectively controls deformation, and ensures safe stability during fully mechanized caving face advancement through abandoned roadways.