Mechanical/Hydraulic Aperture of 3D-Printed Joints in Relation to JRC and Surface Geometry

A thorough understanding of the hydro-mechanical behavior of rock joints is essential since joints typically serve as weak planes and fluid channels within rock masses. Joint roughness, among other factors, dominates the mechanical and hydraulic behavior of rock joints directly. Since 1970s, the joint roughness coefficient (JRC) has been used extensively to quantify joint roughness. As a result of using this variable in empirical equations, we can now anticipate the fluid flow characteristics under stresses. However, the validity of utilizing a single parameter to express the complicated geometry of joint surfaces should be testified. We used three-dimensional (3D) printers to produce a large number of joint samples with similar JRC (2 - 4) but varying surface geometry, including matched and mismatched joint surfaces. The mechanical and hydraulic apertures (E and e) of the printed joint samples were determined utilizing high confining pressure, permeability/porosity measurement equipment (YOKO2). The relationship between E and e can thus be quantified. The results indicate that the stress-dependent mechanical apertures of matched and mismatched joints with similar JRC is significantly different and result in the difference in e-E relationship. However, the measured e-E relationship is quite similar for matched or mismatched smooth joints regardless of joint surface geometry. To conclude, JRC is an appropriate index of smooth joint roughness for representing the stress-dependent e and E and accompanying e-E relationship.