Shear behaviour of fibreglass rock bolts for ground reinforcement

Shear behaviour of fibreglass rock bolts for ground reinforcement

Glass-Reinforced Polymer (GRP) bolts are increasingly used in Australian coal mines as a means of rib support in heading development and for coal-face equipment recovery. Unlike metallic rock bolts, GRP bolts are made through pultrusion resulting in anchor bolts with differing performance characteristics to that of steel. Therefore, previous studies of steel rock bolts could not be utilised to describe the load transfer characteristics of their fibreglass counterparts. This thesis expanded on the shear load transfer mechanisms of fully grouted fibreglass rock bolts utilising a double shear system. Analytical and numerical models were also developed to simulate the shear performance of the fibreglass rock bolts. Two experimental test schemes were carried out. The first with clean shear interfaces and the second with infilled shear interfaces comprised of sandy clay, applied to a thickness of 5mm. Two types of fully grouted rock bolts; 20-tonne and 30-tonne were tested with pretension loads of 0kN, 10kN, 15kN and 20kN. It was found that increasing the pretension also increased the confining pressures at the shear interfaces for both clean and infilled joints. This in turn reduced the damage propagating from the bolt at the shear interface as well as reducing the hinge point bending. Infilled shear interface samples experienced a decrease in the failure displacement while also resulting in an increase to the peak shear force. The analytical model was developed utilising the Fourier transform, energy balance theory and linear elastic theory. The result was an empirical relationship that could determine the double shear performance of fibreglass rock bolts with close agreement to the experimental data. Coefficients were incorporated to facilitate model calibration and tuning. Finally, three-dimensional (3D) modelling was utilised to conduct numerical simulations of fibreglass rock bolts subjected to single shear and double shear scenarios. The numerical model was calibrated against experimental data and then extended to conduct a sensitivity analysis on fibreglass rock bolts subjected to variations of the double shear test parameters. Scenarios included rock bolt installation angles, shearing rates and various host rock strengths. The combined experimental, analytical and numerical studies provide a comprehensive understanding of the shear behaviour of fibreglass rock bolts. By studying the impact of pretension and shear interfaces, this research has successfully modelled the shear failure mechanisms of 20-tonne and 30-tonne fibreglass rock bolts.

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