Numerical simulation study on the mining pressure law and collaborative failure of soft-hard interlayer working face

Aiming at the problem that the roof of the soft-hard interbedded coal seam is prone to delamination and caving without warning during coal mining, taking the No. 2201 working face of a certain mine as the engineering background, a numerical simulation was carried out to study the mine pressure laws and fracture characteristics of the working face with soft-hard interbedded roof. The results show that: when the working face advances 32 m, the roof undergoes the first caving. The fracture angles of the rock formations on the working face side and the open-off cut side are 50° and 47° respectively, and a stable three-hinged arch structure is formed between the roof and the two sidewalls. The roof rock formations are mainly damaged by tension, and then it evolves into vertical stress of mutual extrusion. The overall fracture and the development of cracks are irregular, resulting in large-amplitude, high-frequency and long-time fluctuations in the working resistance of the supports. The tangential tension of the cracks in the soft rock layer induces the failure of the hard rock layer, and the fracture of the hard rock layer intensifies the damage of the soft rock layer in the reverse direction. The two form a mutual feedback mechanism of failure, making the overall strength of the interbedded roof significantly lower than that of a single hard rock layer. This study reveals the disaster-causing mechanism of the coordinated fracture of the soft-hard interbedded roof, which can provide a theoretical basis for roof control.