Characterization of arching effect and failure mode of longwall panel floor

The stress arching mechanism of longwall panel floor were studied by theoretical analysis, numerical simulation and field observation. The study results show that: the direction of the principal stress on the floor is deflected in the process of mining, so the concentrated stress of floor transmits along an arching line. The goaf floor went through a process of high unloading, which intensifies the degree of crack propagation and fracture of the floor. Microcracks in floor are likely to connect with each other to form a macroscopic fracture surface, which leads to a significant volume expansion of goaf floor. There is a terrace-like tensile plastic zone in the goaf floor and an arched shear failure zone exists outside the tensile plastic zone. Field monitoring results reveal that the goaf floor is dominated by unloading tensile failure, and the floor in front of the mining face is dominated by shear failure.