Bearing Characteristics of Rock Joints under Different Bolts Installation Angles and Their Underlying Mechanism

To explore the mechanical failure characteristics of bolted joints under different bolt installation angles and the effect of bolting on the shear strength of joints, a numerical model of structural plane anchoring with different bolt installation angles was established based on the improved Pile element, and a series of uniaxial compression numerical tests were carried out to systematically study the effects of bolt installation angle on bolts. The results show that as the bolt installation angle increases, the peak stress of the specimen is first constant and then decreases, and the elastic modulus of the specimen decreases nonlinearly. When the bolt installation angle is lower than 45°, the bearing capacity of the joints is higher. The interaction between the bolt and the specimen’s force is mainly concentrated at the intersection of the structural plane and the area where the nut gaskets are installed at both ends of the bolt. The horizontal stress is higher in the area where the nut gaskets are installed at both ends of the bolt. With an increase in bolt installation angle, the plastic zone volume of the anchored joint specimen increases linearly with an exponential function. When the bolt installation angle is lower than 45°, the plastic zone volume increases slowly, and when the bolt installation angle is higher than 45°, the plastic zone volume increases rapidly. When the bolt installation angle is small, the contribution of the bolt axial force is greater than that of the bolt shear force. In contrast, when the bolt installation angle is large, the contribution of the bolt axial force is lower than the contribution of the bolt shear force. With an increase in bolt installation angle, the contribution of the bolt axial force decreases nonlinearly, the contribution of the bolt shear force increases linearly, and the shear resistance decreases nonlinearly. The optimal bolt installation angle is about 45°, but the optimal bolt installation angle also changes constantly under the influence of factors such as bolt type, rock strength, and external load.