Investigating shear behaviour of fibreglass rock bolts reinforcing infilled discontinuities for various pretension loads

In this paper, eight shear tests were carried out utilising a double shear with infilled shear interfaces after determining an appropriate experimental design and modified testing scheme. For this, two rock bolts, 20-tonne and 30-tonne, were tested with modified double shear testing apparatus at different pretension loads. The infilled test scheme was conducted with 5mm thick sandy clay infilled shear interfaces. A 40MPa small aggregate concrete was used for all samples to simulate the host rock. Based on the shear profiles, it was found that all samples followed a three-part failure profile consisting of elastic, strain softening and failure regions. The results of double shear tests revealed that the 20-tonne rock bolt saw a significant overall decrease of approximately 30% in its failure displacement response as opposed to the 30-tonne samples’ which saw a 6% increase. Also, it was concluded that the 30-tonne samples outperformed the 20-tonne rock bolts by up to 30%, irrespective of initial pretension settings. Comparing the physical failure characteristics of the samples found that both the 20-tonne and 30-tonne samples exhibited the same response to increased pretension. As the pretension increased, the angle experienced at the hinge point also increased incrementally.