Anisotropy of non-Darcian flow in rock fractures subjected to cyclic shearing

Non-Darcian flow in rock fractures exhibits significant anisotropic characteristics, which can be affected by mechanical processes, such as cyclic shearing. Understanding the evolution of anisotropic non-Darcian flow is crucial for characterizing groundwater flow and mass/heat transport in fractured rock masses. In this study, we conducted experiments on non-Darcian flow in single rough fractures under cyclic shearing conditions, aiming to analyze the anisotropic evolution of inertial permeability and viscous permeability. We established quantitative characterization models for the two types of permeability. First, we conducted cyclic shearing experiments on four sets of 24 rough rock fractures, investigating their shear characteristics. Then, we performed 480 non-Darcian flow experiments to analyze the anisotropic evolution of viscous permeability and inertial permeability of these rock fractures. The results showed that viscous permeability exhibited significant differences only in the orthogonal direction, while inertial permeability exhibited differences in both orthogonal and opposite directions. With increase in the shear cycles, the differences in the orthogonal direction gradually increased, while those in opposite direction gradually decreased. Finally, we established characterization equations for the two permeabilities based on the proposed directional geometric parameters and validated the performance of these equations with experimental data. These findings are useful for the quantitative characterization of the evolution of non-Darcian flow in fractures under dynamic loading conditions.