Effect of Shear Direction Change on Shear-Flow-Transport Processes in Single Rough-Walled Rock Fractures

Abstract

Understanding the shear-flow-transport processes in rock fractures is one of major concerns for many geo-engineering practices, yet the effect of shear direction change on the flow and transport properties through rough-walled rock fractures has received little attention. In this study, a series of shear tests on artificial fractures with different surface roughness are conducted, in which the shear direction is altered perpendicularly. The distribution of apertures and its evolution during shearing are evaluated, which are further applied to simulate fluid flow and solute transport through fractures in the directions parallel and perpendicular to shear direction using a finite element method code. The effect of shear direction change on flow and transport properties of rock fractures is systematically investigated. The results show that when the shear direction is changed perpendicularly during shearing, the normal displacement changes from increasing (i.e., dilation) to decreasing (i.e., closure) with increasing shear displacement. The final normal displacement depends on the competition between dilation and closure induced by the shear in two directions, which directly determines the aperture distribution thereby affecting the flow and transport processes through fractures. The closure is more significant for the fracture with a smaller JRC, resulting in a more dramatic decrease in equivalent permeability. The historical shear stress can either promote or block the solute transport depending on the distributions of void spaces and contact obstacles induced by shearing in two perpendicular directions. The Peclet number decreases during shearing in spite of the magnitude of historical shear displacement, indicating that the dispersion becomes much significant with shearing due to the increasingly concentrated contact areas and flow channels.