Full-scale field pull-out tests on GFRP/BFRP/Steel nailing bars in soil slopes

Steel bars have been widely used as soil slope nailing in highway engineering to avoid slope instability, while concerns have been raised about their corrosion in an aggressive soil environment. Glass fibre reinforced polymer (GFRP) or basalt fibre reinforced polymer (BFRP) bars are associated with better resistance to corrosion and show potentials in such applications, but their bonding performance with concrete is inferior comparing to steel ones. However, associated research is limited to small-scale specimens in laboratorial conditions, and hence further investigations are required. In this study, full-scale field pull-out tests with a maximum bar length of 5.5 m were conducted on three types of bars (i.e., steel, GFRP and BFRP) embedded by grouting in a soil slope. Test results show that the only failure mode of the specimens was the breakage of bars, which was different from laboratorial results. The maximum pull-out forces were therefore determined by the ultimate strengths of the bars, suggesting that a bonding length of 5 m was adequate to exploit the strengths of the bars with a diameter of 22 mm. In terms of the load-slip behaviors, three types of bars showed similar patterns before the yielding of the steel one. The pull-out load distributions in the bars showed an obvious decrease with the distance to the free ends, and such decreases were more obvious for steel bars. The results demonstrate that despite the significant differences in mechanical behavior between FRP bars and steel bars—particularly their lower elastic modulus and anisotropic properties—GFRP and BFRP bars exhibit comparable or even superior pull-out resistance in soil slope nailing applications, offering a corrosion-resistant alternative for highway slope stabilization in aggressive environments.