Experimental study on the pullout behaviour of rockbolts with steel fiber-reinforced grout under constant confining pressures

Deep underground excavation in civil and mining engineering motivates the development of high-strength rockbolting reinforcement. A feasible way to promote the performance of the fully grouted rockbolt is using additives to ameliorate grout properties and thus the bolt-grout interfacial behaviour. Here, we investigated the mechanical behaviour of fully grouted rockbolt specimens in the steel fiber-reinforced grout (FRG) under various constant confining pressures to pullout loading by the self-developed laboratory-scale rockbolt pullout system. We found that the bond strength of the FRG rockbolt specimen can be more than three times high of the plain grout one. The higher the fiber proportion, the greater the bond strength of the FRG rockbolt. When a constant confining pressure was applied, the bond strengths of all the grouted rockbolt specimens were considerably elevated and the bolt rod failure was observed for the FRG rockbolt specimen under 1.0 MPa confining pressure. Compared with the plain grout one, the post-peak failure of the FRG rockbolt specimen of a much higher bond strength was less brittle. The wavy steel fiber performed better in bond strength enhancement and grout cracking mitigation than the straight one mainly due to the crack bridging effect facilitated by its rough geometry. Our experimental studies suggested that FRG rockbolting is promising in reinforcing roadways/tunnels in the deep underground environment.