Research on nonlinear seepage characteristics of rough intersection fractures

Intersection fractures are an important component of the fractured networks in rock masses, and studying the seepage characteristics of intersection fractures is of great significance for revealing the seepage patterns of the entire fracture network in rock masses. By establishing a numerical model of intersection fractures and setting different Joint Roughness Coefficients (JRC) and intersection angles, the Navier-Stokes equations were solved to investigate the nonlinear seepage characteristics of intersection fractures. The results show that there is a nonlinear relationship between the hydraulic gradient and flow rate in intersection fractures,which can both be fitted by the Forchheimer equation. The fracture roughness has a significant impact on the nonlinear seepage characteristics of intersection fractures. As the roughness increases,the critical Reynolds number (Re_c) decreases and the non-Darcy coefficient (β) also decreases. Through analyzing the local flow states,it was found that there is an obvious flow deflection effect after the fluid flows through the intersection, and the water flow tends towards the direction with lower pressure and higher velocity. The existence of this phenomenon was verified by calculating the proportion of outflow. Comparing the maximum velocity and pressure under different initial flow directions, it was found that the seepage direction has a significant impact on the seepage characteristics of intersection fracture.