Experimental study on shear mechanical behavior of bolted rock joints and rock-bolt interaction mechanism

Rock bolting controls shear slip along rock joints, yet the deformation coordination and mechanical response during shearing are not well understood due to complex bolt-rock interaction. This study systematically conducted direct shear tests to investigate how the joint roughness coefficient (JRC), normal stress, and bolt inclination affect the shear behavior of bolted joints. A custom-designed monitoring system was employed to continuously measure the bolt axial force throughout the shearing process. Results indicate that JRC strongly influences bolt deformation and axial-force mobilization through dilatancy, thereby governing the peak and reinforced strengths of the joint. Higher normal stress suppresses joint dilatancy and reduces the bolt’s shear contribution, while bolt inclination controls the balance between axial and shear forces. 45° inclination showed the best overall shear performance. Monitoring data reveal the bolt’s axial force variation during shear displacement progresses through four stages: initial adjustment–relaxation, elastoplastic, hardening, and deformation-failure. This classification tracks how axial force evolves under compatible coordination. Correspondingly, the bolted joint’s shear process develops through elastic, plastic, failure, and residual stages, revealing the mechanical interaction mechanism between the joint surface and bolt at different stages. The study provides an experimental basis for understanding shear behavior of bolted joints and optimizing rock bolt support design.