Influence of coupling mechanism of loose layer and fault on multi-physical fields in mining areas

Coal mining under the geological conditions of a loose layer will lead to the intensification of surface movement and deformation, and mining under the geological conditions of a fault will lead to the living slip of a fault. Mining under both conditions will have a great impact on the safety of coal production. To reveal the evolution law of the coupling mechanism of loose layer and fault on the multi-physical fields of overburden, the numerical simulation method is used to simulate the coupling of loose layer and fault with different thicknesses, analyze the changes of vertical stress on the key strata, the changes of surface subsidence, the evolution of elastic energy on the fault zone and the changes of activated slip area of the fault zone. The simulation analysis shows that the vertical stress change trend of the key strata gradually changes from the "V" shape to the "W" shape at the beginning of mining, and the vertical stress concentration will occur at the fault. The loose layer will promote surface subsidence, and the fault will hinder the surface subsidence to a certain extent. The loose layer and the fault alternately affect the surface subsidence. The elastic energy accumulation on the key strata is mainly concentrated on both sides of the goaf. The elastic energy in the center of the goaf is dissipated. The elastic energy accumulation in the fault zone starts from the shallowly buried fault and gradually develops to the deeply buried fault. The instability of fault activation has gone through the initial stage of activation—the intensification stage of activation—the stable stage of activation. Under the working conditions of no loose layer, thin loose layer, and thick loose layer, the fault zone is the first to undergo living slip, and under the action of an extra-thick loose layer, there is a certain lag in the activation slip of the fault zone.