Influence of dynamic test method on the performance of a mechanically anchored hybrid rockbolt

Authors: Abreu, R; Swart, C

DOI https://doi.org/10.36487/ACG_repo/2625_05

Cite As:
Abreu, R & Swart, C 2026, 'Influence of dynamic test method on the performance of a mechanically anchored hybrid rockbolt', in D Cumming-Potvin & J Wesseloo (eds), Ground Support 2026: Proceedings of the 11th International Conference on Ground Support in Mining, Australian Centre for Geomechanics, Perth, pp. 1-16, https://doi.org/10.36487/ACG_repo/2625_05

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Abstract:
Dynamic rock reinforcement is a critical component of ground support strategies in high-stress underground mining environments, and requires a thorough understanding of how support systems respond under seismic loading. This paper investigates the dynamic performance of mechanically anchored hybrid rockbolts when subjected to both continuous-tube and split-tube laboratory testing configurations. It then explores how a hybrid bolt design can be adapted to include chemical anchorage to improve bolt performance in various loading scenarios and to increase installed bolt longevity. Mechanically anchored hybrid bolts are typically designed for rapid, mechanised installation without the use of resin or grout. These systems comprise a yielding tendon integrated within a mechanically anchored friction unit and are installed using percussive force, followed by rotation of a nut to pretension the assembly and activate a mechanical expansion anchor. This bolt style offers an effective alternative to bonded anchors in conditions where resin or grout is impractical, while delivering improved installation efficiency and suitability across a wide range of ground conditions. Dynamic rockbolts are commonly qualified using laboratory impact testing methods intended to simulate in situ seismic loading. The 2 principal approaches are: continuous-tube, direct-impact testing which simulates rock mass strainburst behaviour split-tube, indirect impact testing which simulates block ejection scenarios. To date, published dynamic testing of hybrid bolts has overwhelmingly favoured continuous-tube methods, which align well with the design of hybrid bolts and their reliance on faceplate loading to activate the end-anchor and facilitate energy absorption through controlled tendon yielding. Limited investigation has been conducted into the performance of mechanically anchored hybrid rockbolts under split-tube, block ejection, loading conditions. In this configuration, the friction unit can partially insulate the yielding tendon from the host-tube or rock mass displacement forces, disrupting the load path between the supported mass and the tendon. This can interfere with proper function of the bolt’s wedge anchor and yielding mechanism. The bolt is then reliant on frictional slip or localised component failure of the friction unit before load transfer to the tendon and activation of the expansion anchor can occur. The paper characterises the load transfer mechanisms acting on the yielding tendon under both dynamic test methods, compares the performance of a conventional hybrid bolt design in continuous- and split-tube configurations, and evaluates targeted design modifications intended to optimise load transfer in both loading scenarios. The outcomes demonstrate improved dynamic performance and repeatability, supporting broader qualification of hybrid bolts for a range of dynamic ground conditions.

Keywords: dynamic ground support, hybrid rockbolt, yielding rockbolt, dynamic rockbolt testing

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