Failure mechanism and 3D physical modeling test of coal face pyramid sliding in steeply inclined working face: A case study

Rib spalling on longwall face is one of the main problems that needs to be solved urgently for achieving safe and efficient mining in steeply inclined coal seams. In order to study the failure mechanism of the coal face in steeply inclined working faces, a 3D physical model of coal face failure is designed in this study; digital speckle technology is utilized to record the deformation and fracture process and failure forms of the coal face; the numerical simulation of coal face stability is carried out from the perspective of "coal face-roof-support" structure; the mechanical model of coal face cone sliding failure is established. The results showed that: when the coal face sustains a large roof pressure, the maximum principal strain reaches 10.76% and the strike displacement is largest. At the same time, the coal face fracture is mainly tensile failure. The maximum displacement along the strike direction is found at the upper part of the inclined seam, followed by the middle and lower part; the serious failure position of coal face along the vertical direction occurs in the upper part of coal face, which is 2/3 of the mining height; the threedimensional displacement of the coal face along the inclined direction is asymmetric. The failure sliding body of coal face starts from the upper layer, then spreads to the lower layer, and finally presents an irregular "quadrangular pyramid" shape. In the "coal face-roof-support" structure, if the support fails or the roof breaks, the coal face will be greatly deformed in depth and height, which will lead to the catastrophe of surrounding rock in the stope. The stability of the coal face can be improved to some extent by properly increasing the working resistance of the support and ensuring the integrity of the tip ⁃to ⁃face roof.