Trapezoidal Failure Behavior and Fracture Evolution Mechanism of Overburden in Extra-thick Coal Mining in Weakly Cemented Strata

The abnormal evolution and highly accurate prediction of mining-induced fractures in extra-thick coal play an important role in mine water disaster prevention and ecological environment protection. The evolution mechanism of mining-induced fractures during the mining of extra-thick coal in weakly cemented strata has attracted wide attention. In this paper, the fracture propagation test and PFC numerical simulation are carried out to analyze the evolution rule of overburden fractures in extra-thick coal mining. Based on the elastic foundation beam and fracture damage theory, we derive a trapezoidal fracture model and realize automatic calculation. Finally, taking the 61,605 working face mining of Longwanggou Coal Mine (LWGCM) as an engineering background, the failure characteristics of overburden are studied and verified by microseismic dynamic monitoring. The results show that the overburden failure in mining face is trapezoidal evolution, including shear fractures (93.8%) and tensile fractures (6.2%). The overburden failure height predicted by the trapezoidal fracture model is consistent with the numerical simulation and microseismic monitoring, the relative errors are − 1.1% and − 2.7%. This provide a new method for the accurate prediction of overburden failure height in extra-thick coal mining in weakly cemented strata.