Study on the deformation and failure mechanisms of a coal wall in a deeply buried longwall working face with a weak roof

Coal wall spall causes serious mining difficulties, especially in deeply buried longwall working faces with a weak roof. To study the deformation and failure mechanisms of the coal wall, the physical model experiments that were conducted using a special loading device that can simulate the formation process of the bearing pressure on the roof rock seam. Combined with numerical simulation, the dominant factors were obtained by sensitivity and weight analyses. The results show that in the advancing process of a working face, the coal seam undergoes a complex fracturing process and the fracturing of the coal seam is closely related to the distance from the coal wall. Both experiment and numerical simulation show that the fracture surfaces near the front face of the coal wall are tensile, but the fracture surfaces away from the front face of the coal wall are shear and tensile or shear. The failure degree of coal wall spall is mainly affected by mining depth, mining height, cohesion, and internal friction angle. These results are useful for understanding the deformation and failure of coal wall.