Effects of roughness on permeability evolution and frictional behavior of fractures under shear

Our experiments investigate the role of roughness in fracture permeability and frictional behavior using artificial fractures with controlled roughness. The results show that (1) Rougher surfaces indicate higher frictional stability and frictional strength due to the presence of cohesive interlocking asperities during shearing, which suggest that rougher fractures are difficult to reactivate. (2) Rough fracture surfaces show velocity strengthening behavior in the initial shearing stage and their strengthening behaviors evolve to velocity neutral and velocity weakening with greater displacement, which means that rough fractures become less stable with shearing (3) The surface roughness exerts a dominant control on permeability evolution over the entire shearing history. Permeability evolves monotonically for smooth fractures but in a fluctuating pattern for highly roughened fractures. A higher roughness is likely to result in more cycling between compaction and dilation during shearing. Significant permeability reduction may occur for rough samples when asperities are highly worn with wear products clogging flow paths. (4) There is no conspicuous correlation between permeability evolution and frictional behavior for rough fracture samples when fractures are subject to sudden sliding velocity change. These lab-scale experimental results reveal the role of rock surface topography in understanding the reactivation and permeability development of fractures.