Numerical simulation of fluid-solid coupling of fractured rock mass considering changes in fracture stiffness

The fluid-solid coupling simulation of fractured coal and rock is helpful to study the influence of the fracture structure on the stress sensitivity of the permeability. Therefore, a key factor in improving the reliability of such a numerical simulation is selecting parameters that match measured laboratory results. This paper firstly illustrates the use of a common inversion method to select the fluid-solid coupling parameters through the constant joint stiffness method (CJSM). The main principle, application range, and the shortcomings of this method (CJSM) are analyzed: It can be used to simulate the measured results in a lower stress range. However, the stress sensitivity of permeability is zero when the stress reaches the critical stress (the stress where the hydraulic aperture reaches the residual hydraulic aperture). In order to solve this problem, a numerical simulation method for fluid-solid coupling using the varying joint stiffness method (VJSM) is proposed based on the characteristic that the compressibility of a fracture decreases with increasing stress. In this method, the compressibility of the hydraulic aperture can be changed by increasing the joint stiffness during the loading process. Thus, the hydraulic aperture can continuously change and there is no need to set the residual hydraulic aperture. Finally, fluid-solid coupling simulations under different stress states were performed using the VJSM in this study. The numerical simulation results were basically consistent with the experimental results, which indicated that a fluid-solid coupling simulation using the VJSM can match experimental results very well and can be further used to study the influence of the persistent fracture angle on the permeability.