Shear Behaviour of Fibreglass Rock Bolts for Various Pretension Loads.

In this paper, after determining an appropriate experimental design and testing scheme to test the shear performance suitably, the impacts of pretension and shear interfaces on fibreglass rock bolts were investigated. For this purpose, at the first stage, the double shear testing apparatus was modified to address the issues and shortcomings of the established testing methodology. Then, 20-tonne and 30-tonne rock bolts were tested with pretension loads of 0 kN, 10 kN, 15 kN, and 20 kN for each test scheme. For this, a 40 MPa small aggregate concrete was used for all samples to simulate the host rock. The grout used to anchor the rock bolts was mixed to the product's recommended guidelines to ensure close resemblance to field mixtures. To maintain consistency, all samples were manufactured with the same concrete and grout recipes. The results of double shear tests revealed that increasing the pretension also increased the confining pressures at the shear interfaces for clean joints. This, in turn, reduced the damage propagating from the bolt at the shear interface and decreased the hinge point bending. The results can be applied for further analytical and numerical studies, which could utilise for a better understanding of the shear behaviour of fibreglass rock bolts. Highlights: Two types of fibreglass rock bolts, the 20-tonne and 30-tonne rock bolts, were tested utilising the modified double-shear apparatus. The double-shear testing apparatus was modified to address the issues and shortcomings of the established testing methodology. The double shear performance profiles of the bolts could be described by three regions categorised as the elastic, strain-softening, and failure regions. Increasing the pretension of each rock bolt type resulted in a reduction in the severity of the recorded shear force dip. The increased pretension yielded less physical damage to the rock bolt propagating away from the shear plane. [ABSTRACT FROM AUTHOR]