Effect of joint microcharacteristics on macroshear behavior of single-bolted rock joints by the numerical modelling with PFC

Joint properties play a controlling role in the strength of rock mass. In response to the situation that existing researches on bolting mechanism of bolted rock joints principally concentrate on the macroelements, such as rock properties, bolting angle and joint morphology, the direct shear tests on unbolted and single-bolted rock joints under the conditions of different normal stress and different joint microproperties by numerical calculation method of particle flow (PFC) were carried out in this paper to reveal the microbolting mechanism and study the influences of joint properties. Subsequently, a comprehensive comparison of microfailure characteristics between unbolted and single-bolted rock joint demonstrated that during the shearing process, a triangle extrusion reinforcement area emerges around the bolt, where microcracks are extremely developed and rock blocks are considerably fractured, but it also improves the anti-shearing efficacy of rock joint. Meanwhile, both the macroshear behavior and microfailure characteristics of single-bolted rock joints with different joint microproperties was analyzed by comparing the shear stress-shear displacement curves and crack development. Specifically, the shear stiffness of single-bolted rock joints enhances with the increase of joint tangential stiffness, and the augmentation of joint tangential stiffness or friction coefficient intensifies the shearing resistance of single-bolted rock joints, whereas the joint normal stiffness was proven to share a negative correlation with the shear strength of single-bolted rock joints. Besides, the shear stiffness of single-bolted rock joints decreases approximately linearly with the increasing joint thickness. In addition, the thicker the joint, the lower the peak shear stress of single-bolted rock joints. With the increase of joint thickness, the crack number of single-bolted rock joint failure decreases, and the particle confinement of bolt is enhanced.