Morphological features of shear-formed fractures developed in a rock bridge

Rock bridges are commonly encountered in incipiently jointed rock masses, and the problem of their failure has a significant influence on the safety of involved engineering practices. Although many research have been conducted to look into the geometrical or mechanical properties of rock bridges before failure, the properties of them after failure have rarely been investigated. In this study, we carried out an investigation on the morphological features of newly-formed fractures developed in a rock bridge. The influence of the applied normal stress and the joint persistence on the fracture morphology was systematically examined in terms of failure mechanism and Grasselli's model. The research results demonstrated that the development of the fractures in a rock bridge can be attributed to tensile failure mechanism or shear failure mechanism. It was found that the tensile failure mechanism produces more curvilinear and rougher fractures than the shear failure mechanism. Moreover, the fractures developed in a rock bridge were anisotropic with asymmetric asperities along the shearing plane (i.e., maximum possible contact area, A(0), is less than 0.5), which is considerably distinguished from that developed in an intact rock through splitting. The present study would promote our knowledge of rock bridges, and contribute to the development of shear strength criterions.