Investigating the seepage behavior through rough fractures during rotational shearing

This study explores the effects of confining pressure Pz, shear displacement u, and rotational shear angle θ on the nonlinear hydraulic behavior during the rotational shearing of rough rock fractures. A model for fractures under rotational shear was first established, and subsequent seepage tests were carried out at various flow rates. The data revealed a strong correlation between the hydraulic gradient and flow rate by Forchheimer's law. The coefficients of the inertial and non-inertial terms of Forchheimer's law decreased in two distinct phases with increasing u. Both Pz and θ were found to enhance these coefficients, with the effect being more pronounced at a smaller u. The critical Reynolds number Rec increased by up to 2.58 times as u ranged from 1 to 15 mm, with a higher Pz and the θ corresponding to lower Rec values. The Forchheimer coefficient decreased rapidly with increasing u due to dilatancy effects, and the rate of decrease slowed as these effects diminished. Increases in Pz and θ led to a concomitant rise in β, although the influence of u and Pz on β was mitigated by the increase in θ. By solving the Navier–Stokes equations, simulations of the seepage flow in a fracture under rotational shear were conducted. The simulation results indicate that as rotational shearing occurs, the number of streamlines within the fracture decreases, while the number of vortices increases. The findings may offer some insight for underground space development projects.