A cohesive-frictional elastoplastic constitutive model for rock joint

Rock joints always have a smaller strength, and it plays an important influence on the overall strength of rock mass. The mechanical behavior of rock joints is mainly governed by the surface topography, normal stress, and failure degree. In this study, a series of direct shear tests for four different rough rock joints under five normal stresses was carried out. The shear and normal stiffnesses were first determined, and the shear shrinkage effect was represented by a shear-normal coupling coefficient. Assuming that the strength of the joint is composed of frictional and cohesive parts, the evolutions of cohesion, friction angle with joint roughness coefficient (JRC), and plastic shear displacement are obtained. The dilatancy behavior is described by the dilation angle, which is considered a function of JRC, plastic shear displacement, and normal stress. A cohesive-frictional elastoplastic constitutive model is hence proposed. The theoretical curves under constant normal stress conditions of the proposed model are in good agreement with the experimental results. The shear behaviors under constant normal stiffness and constant normal displacement conditions can be predicted using the new constitutive model.