An experimental investigation on the dynamic shear characteristics of wet joints

Abstract

This study investigated the dynamic shear behavior of planar granite joints under dry and wet conditions using the impact-induced direct shear test. The effects of shear rate and normal stress on the dynamic shear properties were examined on dry and wet joints under four different normal stress conditions. Dynamic shear stress and shear displacement were measured by stress wave acquisition and digital image correlation method, respectively. Dynamic friction coefficients were calculated using the Mohr-Coulomb criterion. Additionally, fracture energy was calculated and compared with nano-indentation tests. The results revealed that moisture significantly alters the dynamic shear response of rock joints. Although both dry and wet joints exhibited dynamic shear stress–displacement curves consisting of two stages, namely a shear stress accumulation stage and a slip stage, the wet joints displayed notably greater strength degradation. A linearly decreasing relationship between maximum shear displacement and normal stress was observed for both joint types. Within the shear displacement rate range of 4–6 m/s, both dry and wet joints exhibited a negative rate effect, wherein dynamic shear strength decreases with increasing shear rate. Wet joints showed a significant 53.2 % reduction in dynamic friction coefficient, compared to 33.9 % for dry joints. Nano-indentation tests further revealed differences in microscale mechanical behavior between dry and wet joints. Compared to dry joints, wet joints showed a 74.2 % increase in maximum indentation depth and a 50.69 % reduction in fracture energy. These findings suggest that wetting-induced strength weakening of rock joints was governed by reductions in fracture energy and frictional properties.