Fluid flow in rock fractures is significantly influenced by cyclic shear. This phenomenon arises due to seismic activity or repeated stress changes resulting from excavation, blasting, and operational loads. In this study, experiments are carried out to investigate non-Darcian flow in single rough fractures after cyclic shearing. The evolution of inertial and viscous permeability is analyzed, and a predictive model for non-Darcian flow is established. Cyclic shearing experiments are first conducted to examine shear characteristics and geometric variations, using four groups comprising 24 rough rock fractures. Subsequently, 360 non-Darcian flow experiments are performed to study the evolution of inertial and viscous permeability under cyclic shearing. It is observed that both types of permeability tend to decrease with an increasing number of shearing cycles. The most significant reduction occurs during the first cycle, followed by a slower decline that eventually stabilizes. A predictive model for non-Darcian flow is then developed, considering the geometry before shearing, rock properties, and cyclic shear characteristics. This model is validated against experimental data. Based on the proposed predictive model, a method for determining the critical number of shear cycles is also proposed. These findings contribute to understanding the evolution of non-Darcian flow in fractures subjected to seismic activity or repeated stress changes.

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 nonDarcian 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.

Inertial permeability is a critical parameter that quantifies the pressure loss caused by inertia in fluid flow through rough-walled fractures, described by the Forchheimer equation. This study investigates the size effect on the inertial permeability of rough-walled fractures and establishes a characterization model for fractures of varying sizes. Numerical simulations are conducted on five large-scale fracture models (1 m x 1 m) by resolving the Navier-Stokes equations. Smaller models are extracted from these large-scale fracture models for detailed size-dependent analysis. The results show that the peak asperity height (xi), asperity height variation coefficient (eta), and the fitting coefficient of the aperture cumulative distribution curve