Shear behavior of rock joints reinforced with fully-grouted and energy-absorbing bolts subjected to shear cycles

In geotechnical engineering, rock bolts are commonly used for reinforcement, while the surrounding rock mass bears varying degrees of shear loads. The shear rate affects the stability of bolted rock joints, especially in projects susceptible to dynamic shear loads. In laboratory experiments, fully-grouted bolts and energy-absorbing bolts were used as research objects, and artificial rock specimens with rough joints were fabricated to analyze the shear characteristics and damage mechanisms of bolted rock joints under cyclic shear conditions and different shear velocities. The results showed that as the shear rate increased, the shear strength of bolted rock joint specimens decreased. Degradation of asperities resulted in no obvious peak shear stress in the specimens. Energy-absorbing bolts exhibited greater deformation capacity, with significant necking phenomena and the ability to withstand larger shear displacements. In contrast, fully-grouted bolts, which have threaded surfaces that provide higher bonding performance, exhibited a reduced capacity for plastic deformation and were prone to breaking under smaller shear displacements. Although the shear stiffness of specimens reinforced by energy-absorbing bolts was slightly lower than that of fully-grouted bolt specimens, they demonstrated greater stability under various shear rates. The absorbed shear energy showed that energy-absorbing bolts had superior coordinated deformation capabilities, thus exhibiting greater absorbed shear energy than fully-grouted bolts. Overall, fully-grouted bolts are more suitable for projects requiring higher rock shear strength and overall stiffness. In contrast, energy-absorbing bolts are more suitable for coping with dynamic or fluctuating load conditions to maintain the relative stability of jointed rock masses.