Shear creep characteristics and creep constitutive model of bolted rock joints

The shear creep behavior of bolted rock joints is closely related to the long-term stability of bolt-reinforced high slopes and underground caverns. To investigate the controlling effect of bolts on rock joint shear creep, limestone samples from the Wudongde dam site area in southwest China were collected and processed, and multistep shear creep tests were conducted on both bolted an unbolted rock joints. The results show that the shear creep of bolted rock joints includes the instantaneous strain stage, transient creep stage and steady-state creep stage, yet the accelerating creep typically occurs instantaneously and is unobservable. By comparing the shear creep process of bolted and unbolted rock joints, it is observed that the presence of bolts decelerates the deterioration of joint surfaces, resulting in a shorter duration of transient creep and lower creep rate. Furthermore, the bolt alters the creep failure mode of the rock joint from brittle failure to plastic failure. Based on experimental results, the reinforcement effect of the bolt through joint creep is analyzed, and the stress evolution during creep is divided into three stages, i.e., the stress-compatibility stage, the stress-compensation stage, and the stress-limitation stage. We summarize how the bolt compensates for stress loss caused by joint surface deterioration through increased shear and axial forces, thereby reducing the creep rate and creep deformation of the rock joint. Based on the stress compensation mechanism of the bolt, a B-Q-N (Burgers-shear force Qo-axial force No) creep constitutive model for bolted rock joints is proposed. When the creep behavior of the unbolted rock joint and the anchorage parameters are known, the B-Q-N model can describe the shear creep behavior of bolted rock joints without experimental data for parameter identification, as well verified by our tests.