Development of Novel Braided Fibreglass (FG) Rock Bolts with Robust Shear Strength Properties-Part II: Large-Scale Mechanical Performance Evaluation

Abstract The limited shear capacity and brittle failure of conventional pultruded glass fibre-reinforced polymer (GFRP) rock bolts continue to restrict their application, despite advantages such as corrosion resistance and cuttability. To address this, our earlier study (Paper 1) developed braidtrusion-manufactured prototypes of GFRP rock bolts infused with graphene–epoxy matrices and identified two optimised designs, RE6 (22 mm) and RE7 (35 mm), that demonstrated promising improvements in shear capacities in guillotine shear tests. While these laboratory-scale findings confirmed the potential of the new manufacturing process, they did not capture the full spectrum of loading conditions experienced underground. This paper presents the second stage of the research programme, focussing on the large-scale mechanical evaluation of the RE6 and RE7 prototypes. A comprehensive experimental scheme was undertaken, including concrete-embedded double-shear tests, double-embedment pull-out tests, axial tensile tests, and torsion tests, designed to replicate realistic service conditions. The results demonstrated that shear capacity was strongly influenced by diameter: RE7 achieved a peak double-shear load of 266.9 kN compared with 185.5 kN for RE6, both showing stable post-peak behaviour. In axial pull-out tests, peak capacities of 414.6 kN (RE7) and 309.7 kN (RE6) were recorded, with failure governed by progressive debonding rather than abrupt rupture. Double-embedment tensile tests returned high peak loads with controlled post-peak softening rather than brittle failure, RE6 reached 330.5 kN at 15.1 mm and RE7 452.7 kN at 19.4 mm, with debonding governed by rib–grout interaction and no tendon damage observed. Torsion tests revealed maximum torques of 1.02 kN·m for RE7 and 0.50 kN·m for RE6, with no damage observed. By linking the manufacturing innovations reported in Paper 1 with systematic large-scale validation, this study established a modified manufacturing process of fibreglass rock bolts as high-capacity, energy-absorbing alternatives to steel rock bolts, capable of addressing the shear limitations that have historically constrained GFRP applications in mining and civil ground support.