Performance in shear of mechanical hybrid rockbolts

Authors: Knox, G; Hadjigeorgiou, J Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2325_33

Cite As:
Knox, G & Hadjigeorgiou, J 2023, 'Performance in shear of mechanical hybrid rockbolts', in J Wesseloo (ed.), Ground Support 2023: Proceedings of the 10th International Conference on Ground Support in Mining, Australian Centre for Geomechanics, Perth, pp. 495-506, https://doi.org/10.36487/ACG_repo/2325_33



Abstract:
The performance of a rock reinforcement system is a function of successfully matching a rockbolt to ground conditions and the quality of installation. In very heavily fractured ground, the installation of resin or cementitious grouted rockbolts can be challenging. This is due to resin losses within the fractures and voids surrounding the borehole, as well as ‘blown out’ holes and hole closures. Poor installation can result in quality issues which may prevent a ground support system from achieving its specified performance requirements. In adverse ground conditions, where it is difficult to install grouted rockbolts, a mechanical hybrid rockbolt may provide an alternative. The typical configuration of a mechanical hybrid rockbolt is a steel tendon mechanically anchored within a friction rock stabiliser. The rockbolt is installed using a percussion force applied by the rockdrill, and the mechanical anchor is subsequently activated using rotation. This installation process improves the rockbolt’s resilience to hole closures. The absence of a chemical anchoring medium in this configuration reduces the impact of fractures and voids on the performance of the rockbolt. Recent work has focused on quantifying the performance of a mechanical hybrid rockbolt when subjected to a pull or impact test. These investigations employed testing configurations where the loading was applied to the thread of the tendon, or the plate affixed to the tendon. Scant information is available on the performance of mechanical hybrid rockbolts when the rockbolt is subjected to either an axial or shear indirect loading case, which are common in fractured rock masses. This paper describes the methodology and the results of an investigation into the performance of the mechanical hybrid rockbolt when subjected to indirect axial pull testing and shear loading. The investigation was conducted under laboratory-controlled conditions and resulted in consistent and repeatable results.

Keywords: shear testing, mechanical hybrid rockbolt, laboratory conditions

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