Discrete Element Numerical Simulation Method for Permeability Stress Sensitivity of Persistent Fractured Coal Samples

The stress sensitivity of the persistent fracture and primary joint directly affect the stress and permeability of elastic and shear fracture coal samples in fluid–solid coupling simulation. Therefore, the method to select the parameters of the primary joints and persistent fracture affects the accuracy and reliability of the numerical simulation. This paper introduces the discrete element flow coupling simulation program based on the cubic law. The research on the relationship between flow rates and model parameters, including the mesh number, practice length, aperture, model size, and pressure difference, were performed. The fitting formulas of the flow rates and model parameters were obtained by numerical simulation. Based on the experimental study on the stress permeability of the elastic coal sample and the persistent fracture coal sample, the fluid–solid coupling simulation parameters selection method of the initial joint and persistent fracture is presented. The numerical simulation results with the calculation parameters under triaxial equi-compressive and deviatoric loads are in good agreement with the experimental results, indicating that the method herein can well simulate the relationship between the stress and permeability of the coal samples.