Geometric and mechanical properties of a shear-formed fracture occurring in a rock bridge between discontinuous joints

Abstract

Rock bridges are commonly encountered in rock engineering practices and play a significant role in the stabilization of rock masses. Under shear loading, they are supposed to provide resistance not only at before-failure stages, but also at after-failure stages, and this is not fully understood yet by now. To promote the solving of this problem, the present study tried to discover the geometric and mechanical properties of a shear-formed fracture occurring in a rock bridge between discontinuous open joints through laboratory experiments. After careful preparation of sandstone specimens containing discontinuous open joints, a series of direct shear tests were carried out under constant normal load (CNL) conditions. Once the rock bridge failed, another two sets of cyclic loading were subsequently applied to the specimen to examine the after-failure properties. The geometric properties of the newly formed fracture in rock bridge area, including undulating angle, fracture roughness, and fracture aperture, were systematically examined and analyzed with respect to the applied normal stress and joint persistence. Furthermore, the failure mode was dependent on the normal stress and joint persistence and also influenced the properties of the shear-formed fracture. Accordingly, different fracture types occurring to the rock bridges were summarized and described in terms of geometric morphology. The findings in present study would enhance our understanding of the influence of rock bridges, especially at after-failure stages, on engineering practices such as rock slopes.