Effect of block caving mining disturbance on the permeability characteristics evolution of fractured rock mass

Disturbances caused by block caving mining can significantly change the geometric parameters of rock fractures and affect the hydraulic characteristics of the rock mass. In areas with heavy rainfall, there is a high risk of water gushing into mining roadways if the overlying rock mass becomes highly permeable. Therefore, it is extremely important to find out the changes in permeability characteristics of surrounding rock mass under caving mining disturbance. In this research, fracture parameters, including fracture orientation, aperture, density, and trace length, before and after mining activities, were obtained via fracture mapping. Discrete fracture networks were established based on these fracture parameters using the Monte Carlo method, and then seepage simulations were carried out with a MATLAB program. The variations of permeability characteristics of rock mass under block caving mining disturbance, including representative elementary volume for permeability (REV-P), principal permeability direction, and principal permeability coefficients, were obtained. Results show that this seepage simulation method can accurately calculate the permeability coefficients, compared with field test results. After mining disturbance, the mean trace length of fractures and REV-P size increase by about 40%; the principal permeability direction changes from 164.53 to 143.63°, and the maximum principal permeability coefficient increases by 6.6 times, which is mainly influenced by the changes of fracture trace length and aperture due to block caving mining disturbance.