Study on physical aperture and fluid flow behavior after dislocation of a rough fracture

Fractures strongly influence fluid flow and shear behavior in rock masses. However, direct testing on natural rock fractures is limited by scale, repeatability, and difficulties in controlling fracture geometry, particularly under dislocation. This study examined the effects of fracture dislocation on physical aperture, roughness, and fluid flow in a single induced tensile fracture of Kuru granite. Furthermore, it combined high-resolution photogrammetry and 3D printing to evaluate the feasibility of using fracture replicas for fluid flow testing. A fracture measuring 6 cm × 6 cm was analyzed using high-resolution photogrammetry, and 3D models of well-matched and dislocated surfaces were used to quantify aperture and roughness. Results showed a nonlinear increase in physical aperture with dislocation up to the maximum tested dislocation of 5 mm, accompanied by a decrease in surface roughness. A custom fluid flow setup was developed to test both natural and printed samples under varying hydraulic pressure gradients. Flow tests demonstrated that dislocation enlarged hydraulic apertures and increased flow rates, following a nonlinear relationship with hydraulic pressure gradient. Forchheimer's analysis indicated that hydraulic aperture (e h ) and the non-Darcy coefficient (β) are direction-dependent and highly sensitive to the magnitude of dislocation, resulting in flow anisotropy, jointly controlled by aperture and roughness. Comparisons between natural and printed samples revealed consistent flow trends but overestimated hydraulic apertures compared to the natural rock. The findings highlight the suitability of 3D-printed replicas for controlled fracture flow studies, while underlining current challenges in replicating natural roughness due to limitations in 3D printing and photogrammetry.