Towards boundary conditions in concrete-rock joint shearing with STAs profile by PFC2D

Abstract

Boundary conditions significantly affect the shear behavior of concrete-rock joints. Most of the joint models have been developed for the constant normal load (CNL) conditions but cannot be directly extended to the more general constant normal stiffness (CNS) conditions, as a ‘normal stiffness (K)’ serves as a spring in such a condition to constantly adjust the normal confinements in terms of the dilation. In this study, the authors attempted to set up numerical modeling of concrete-rock joint shearing by layered over-compaction method based on PFC2D. An obvious extension is that explicit spring-based kinetic equations were employed to govern the travel of the upper shear chamber, by which the system can be dynamically balanced at each timestep to permit CNS conditions. Also, an alternative joint profile consisting of multiple similar triangular asperities (STAs) was defined in the presented modeling, taking account of both varied asperity heights and sizes. The comparisons with laboratory observations, recently published by the authors, demonstrated that the model makes reasonable predictions of shear behavior, especially well capturing the essential mechanisms of STAs profile, including dilation, shearing, and local lift-off. Compared with CNL conditions, the CNS conditions can better mobilize the peak shear strength, maximum normal stress, micro-cracks, and force chain. Results indicate that an adequate choice of CNL or CNS conditions is of significance to evaluate the side resistance, loading capacity, or engineering stability in geotechnical engineering practices.