Nonlinear Dilatancy Seepage Model of Single Rock Fracture with Shear Broken

The seepage behavior of a single fracture under the coupled shear–seepage condition is important to the stability of rock mass, especially when shear broken. In this study, coupled shear–seepage tests are conducted on regular tooth single rock fracture with radial fluid flow. The shear failure and changes in the dilation angle were investigated with 1.27, 1.59, 1.91, 2.23, and 2.55 MPa normal stress; the nonlinear seepage behavior was analyzed with 0.2, 0.4, 0.6, and 0.8 MPa hydraulic pressure, and shear broken. The results show that during the shearing process, the nonlinear changes in shear strength, normal deformation, and the dilation angle show great differences with shear displacement, which could be divided into the peak shear, softening shear, and residual shear displacement sections under the influence of shear broken and gouge material. In the peak shear displacement section, normal deformation increased rapidly when the dilation angle was constant; in the softening shear displacement section, normal deformation increased slowly when the dilation angle rapidly decreased, and the normal deformation and dilation angle tended to be stable in the residual shear displacement section. The relationship between the hydraulic gradient and flow rate was consistent with Forchheimer’s law, and the linear and nonlinear term coefficients in Forchheimer’s law show a negative power and negative exponential function with shear displacement, because the joint surface roughness and the degree of the uneven aperture decreased with the influence of shear broken and gouge material. In addition, the values of the mechanical aperture were much larger than the hydraulic aperture, the ratio between the mechanical and hydraulic apertures increased, and decreased nonlinear taken peak shear displacement as the dividing point. Finally, the nonlinear dilatancy seepage model was established by considering the changed dilation angle and hydraulic gradient during the shear process. This study could be a basis for the coupled shear–seepage analysis of network rock mass and similar studies.