Modeling of softening and hardening behaviors of the shear strength of rock joints

In shear tests of rock joints, constant normal load(CNL), constant normal displacement and constant normal stiffness(CNS) conditions are used. Compared to the first two conditions, Shear stress-displacement curves display more complicated in the case of CNS condition. Aiming to evaluate shear behavior of rock joints under CNS, an extension was made to model strength softening and strength hardening processes in a unified form on the basis of the approach which takes strain softening process as a series of stress drop and plastic flow, and the corresponding formulation was presented. Shear behavior was modeled under various CNS conditions. The results show that shear stress-displacement curve displays in strength softening mode when the normal stiffness is small but that strength hardening mode appears while the normal stiffness increases. The shear stress-shear displacement curves, normal displacement-shear displacement curves and normal stress-shear displacement curves were compared with test results and good agreements between them were observed, which indicates that the presented procedure is reliable. Furthermore, the shear behavior of rock joints was studied under different combinations of the initial normal stress and the normal stiffness. © 2018, Science Press. All right reserved.