Experimental study on the mechanical properties of GFRP bolts: Insights from failure modes and adhesion strength of the rod-grout interface

In underground float-resisting engineering, glass fiber reinforced polymer (GFRP) bolts are becoming more and more popular as substitutes for conventional steel float-resisting bolts due to their superior mechanical properties and corrosion resistance. The differences in failure modes between GFRP and steel float-resisting bolts, ultimate loads, and bond-slip curves were explained in this paper using full-scale destructive pull-outs. It also demonstrates how various influencing factors affected the adhesion strength at the rod-grout interface of GFRP float-resisting bolts. The results indicated that shear slip and bolt fracture were the predominant failure modes for both GFRP and steel float-resisting bolts. Compared to steel float-resisting bolts of the same specifications, the failure loads of GFRP float-resisting bolts with anchorage lengths of 4.5 m and 6.5 m were 21% and 14% higher, respectively. Compared to steel float-resisting bolts, the adhesive properties at the rod-grout interface of GFRP float-resisting bolt were superior. Anchorage length, bolt material, and bolt diameter are key variables, listed in descending order of influence, determining the adhesion strength at the rod-grout interface of float-resisting bolts. Steel float-resisting bolts with longer anchorage lengths and greater bolt diameters may be replaced by GFRP float-resisting bolts with shorter anchorage lengths and smaller bolt diameters. • Full-scale tests: 8 GFRP and 6 steel bolts show performance comparisons. • GFRP and steel bolt bond behavior and failure modes analyzed with bond-slip curves. • Bolt material, diameter and anchorage length are the main adhesion strength factors.