Authors: Venter, DL; Knox, G

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Venter, DL & Knox, G 2023, 'Effect of mobilised length on the performance of a paddled energy-absorbing rockbolt', in J Wesseloo (ed.), Ground Support 2023: Proceedings of the 10th International Conference on Ground Support in Mining, Australian Centre for Geomechanics, Perth, pp. 507-518,

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Energy-absorbing rockbolts have become widely accepted as a best practice where the anticipated failure mode of the rock mass may result in rockbursts. The prolific application of the paddled energy-absorbing rockbolt within the industry is a result of the installation method and the energy capacity demonstrated through laboratory impact testing and a series of well-documented field trials. The design of the paddled energy-absorbing rockbolt is a debonding length of smooth steel bounded by two anchor points. When a load is applied to the rockbolt, the debonding length of steel bar is mobilised and plastically deforms, absorbing energy. Consequently, the capacity of the rockbolt is directly correlated to the mechanical and geometric properties of the steel bar from which it is produced. The specific capacity of a paddled energy-absorbing rockbolt is determined through split tube impact testing, and it is common practice to calculate an energy absorption rate in kJ/m. Due to the limited data and geometric constraints of the test equipment, these values are often used to calculate the capacity of a rockbolt when the length of the debonding length varies. The variation in the debonded length can result from either a relocation of the anchor points along the length of the rockbolt or a variation in the length of the rockbolt. This paper presents the results of a controlled investigation demonstrating the effect of the debonding length on the performance of a paddled energy-absorbing rockbolt through a series of laboratory-based impact tests. The debonding length of the paddled energy-absorbing rockbolt was varied by altering the length of the tendons produced from the same batch of steel, to limit the variation in the mechanical properties of the samples. The investigation demonstrates that the practice of extrapolating to longer mobilised lengths, using data generated from shorter debonded length samples, can result in an over estimation of the energy absorption capacity of a rockbolt.

Keywords: rock reinforcement design, dynamic impact testing, debonded length, energy-absorbing rockbolt

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