Laboratory investigation of effect of gouge material on closure during shearing

In this work, the effect of gouge materials on the non-linearity of the closure curve during shear was investigated in the direct shear tests by using mortar fracture replicas of sizes ranging from 100 mm to 200 mm, which were reproduced from a tensile fracture created in granite. Monotonic shear loading was applied at normal stresses of 0.3 and 1 MPa for shear displacements of 2 and 20 mm. The results showed that the non-linearity of the closure curve during shear increases with the presence of the gouge materials/debris that are produced in the shearing process. This is mainly because the gouge is soft to easily deform under the applied normal stress and the gouge materials are distributed non-uniformly around the contact areas. Thus, the normal stiffness during shear decreases not only with the decreasing matedness between the surfaces, but also with the presence of gouge materials.