Experimental study of a borehole repairing and strengthening device for improving the performance of resin-anchored bolts in soft and broken surrounding rock

During the process of resin-anchored roof bolting in soft and broken surrounding rock, the fractures in the borehole wall can result in resin loss, affecting resin distribution and anchoring quality. In the paper, we developed a borehole repairing and strengthening device (BRSD) for resin-anchored bolt systems. Theoretical analyses, numeric al simulations, laboratory experiments and in situ test were performed to explore the resin flow characteristics given fractures, as well as the working principle of the device. The key parameters of the device were then optimized, and the working performance of the device was verified. The results indicate that the resin and the curing agent rapidly flow into the fractures subjected to bolt mixing. Increasing resin loss, fracture aperture, and number of fractures can cause the mean bonding stress to exceed the ultimate bonding strength of the interface between the resin and the surrounding rock. The developed BRSD has a good working performance. The resin mixer enables the resin to be discharged at a higher flow velocity from the resin container. The rib for resin daubing of the resin container can effectively and quickly daub the resin into the fractures. The device can reduce the number of fractures and the fracture aperture and form a regenerative borehole wall composed of rock fragments and resin in large broken areas. As a result, the anchoring length and the bearing capacity of the anchoring system are significantly improved. This study may provide a theoretical reference for the stability control and anchoring quality improvement of soft and broken surrounding rock.