Numerical simulation of fractured water-conducting zone by considering native fractures in overlying rocks

The height of the fractured water-conducting zone(FWCZ) is vital to the mine safety and the ecological environment protection of the mining areas. Previous numerical simulation method which judge the range of the fractured water-conducting zone through plastic zone can not fully reflect the failure mechanism of overburden. In order to predict the height of FWCZ more accurately, the fracture criterion of rock in the presence of native fracture is proposed by combining the fracture criterion of stress intensity factor with the Mohr-Coulomb yielding criterion. Native fracture field was constructed with self-affine fractal model and the finite element analysis software COMSOL Multiphysics was utilized to apply the native fracture field and the rock fracture criterion to the numerical simulation of the FWCZ's development in Qingdong Coal Mine. The results show that the height of FWCZ reaches 92.5 m when considering the native fractures. In contrast with the traditional "plastic zone" method and empirical formula method, the ratio of the height of the FWCZ to the mining height in the proposed method is closer to the field measured value, indicating that the fracture field generated by the self-affine fractal model can appropriately simulate the complex and disordered distribution of native fractures in rock mass. Therefore, the proposed method could better reflect the development mechanism of fractured water-conducting zone.