Hydromechanical properties of 3D printed fractures with controlled surface roughness: Insights into shear-permeability coupling processes

We explore the potentials of three-dimensional (3D) printing to explore hydromechanical processes in laboratory-scale fractures. 3D printing enables replication of designer fractures with quantified and repeatable roughness to examine the interdependencies between mechanical and hydraulic response including, for example, the Barton-Bandis model. The present study successfully probes subtle variations of shear strength and dilation behavior in 3D printed fractures controlled by surface roughness. For constant materials and basic frictional characteristics, shear strength increases with increasing the standard deviation of the surface height with dilation rate principally controlled by the average amplitude of the long period wavelength of the fracture surface and insensitive the secondary (minor amplitude) roughness. Importantly, these sensitivities are manifest in the permeability response. With increasing shear displacement, the fracture permeability first decreases and then increases with oscillations resulting from step changes in fracture-fracture contact architectures. As these distinctive behaviors are consistent with those of real rock fractures, we conclude that 3D printed fractures provide a useful analog to real rock fractures when constraining slip-permeability coupling during shear slip.