Internal mechanism of asymmetric deformation and failure characteristics of the roof for longwall mining of a steeply dipping coal seam

Stability control of the roof is the key to safe and efficient mining of the longwall working face for a steeply dipping coal seam. In this study, a comprehensive analysis was performed on the roof destruction, migration, and filling characteristics of a steeply dipping longwall working face in an actual coalmine. Elastic foundation theory was used to construct a roof mechanics model; the effect of the coal seam inclination angle on the asymmetric deformation and failure of the roof under the constraint of an unbalanced gangue filling was considered. According to the model, increasing the coal seam angle, thickness of the immediate roof, and length of the working face as well as decreasing the thickness of the coal seam can increase the length of the contact area formed by the caving gangue in the lower area of the slope. Changes to the length of the contact area affect the forces and boundary conditions of the main roof. Increasing the coal seam angle reduces the deformation of the main roof, and the position of peak deflection migrates from the middle of the working face to the upper middle. Meanwhile, the position of the peak rotation angle migrates from the lower area of the working face to the upper area. The peak bending moment decreases continuously, and its position migrates from the headgate T-junction to the tailgate T-junction and then the middle of the working face. Field test results verified the rationality of the mechanics model. These findings reveal the effect of the inclination coal seam angle on roof deformation and failure and provide theoretical guidance for engineering practice.