Influence of Top-Coal Stopping and Presplitting Roof Cutting on Stability of Withdrawal Channel in Final Mining of Fully Mechanized Top-Coal Caving Face in Extra-Thick Coal Seam

With the increased extraction thickness in fully mechanized top-coal caving faces in extra-thick coal seams, the caved gangue in the goaf is unable to effectively support the roof, resulting in aggravated deformation of the pre-driven withdrawal channel. Taking the No. 221304 working face in the No. 13 coal seam of Xiaojiawa Coal Mine as the engineering background, this study combined theoretical analysis, numerical simulation, and field measurement to investigate the effects of the top-coal caving stopping position, suspended roof length, and presplitting roof cutting on the stress and deformation of the rock surrounding the withdrawal channel. The results indicate that the convergence of the roof and floor and that of the two ribs of the withdrawal channel decrease in a staged manner with the increase in the top-coal caving stopping distance, but increase nonlinearly with the increase in the suspended roof length. With the increase in the presplitting roof-cutting height, the surrounding rock deformation first decreases significantly and then tends to level off. When the roof-cutting height is 30.5 m, the reductions in roof displacement and rib convergence reach 33.46% and 37.76%, respectively. When the roof-cutting height is further increased to 35.0 m, the improvement becomes insignificant. Therefore, the reasonable roof-cutting height for the No. 13 coal seam is determined to be 30.5 m. Field monitoring results show that the convergence of the roof and floor and that of the two ribs of the withdrawal channel are reduced by 41.2% and 36.8%, respectively, and the distance between the stopping line and the terminal mining line is shortened by 15 m. The research results provide a useful reference for determining the top-coal caving stopping position and roof-cutting height, and for improving the stability of the surrounding rock of the support withdrawal channel during the final mining stage of fully mechanized top-coal caving faces with thick and hard roofs in extra-thick coal seams.