Coaxial load development along grouted plain strand cable bolts determined by distributed fibre optic strain sensing

Authors: Forbes, B; Vlachopoulos, N; Diederichs, MS

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DOI https://doi.org/10.36487/ACG_repo/2325_32

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Forbes, B, Vlachopoulos, N & Diederichs, MS 2023, 'Coaxial load development along grouted plain strand cable bolts determined by distributed fibre optic strain sensing', in J Wesseloo (ed.), Ground Support 2023: Proceedings of the 10th International Conference on Ground Support in Mining, Australian Centre for Geomechanics, Perth, pp. 479-494, https://doi.org/10.36487/ACG_repo/2325_32

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Abstract:
This paper is focused on the mobilisation of coaxial load and displacement along grouted plain strand cable bolts during laboratory coaxial pull testing. In comparison to the existing body of work on cable bolts, this research has investigated grouted cable lengths in excess of a metre. As a result, the load distributed along the cable bolts was not uniform during loading and required many discrete sensing locations to be measured. To this end, a high spatial resolution distributed fibre optic strain sensing technology was used to measure a nearly continuous coaxial load distribution along each cable bolt that was tested. Load development length was measured to increase from the loaded end to the free end of the cable with increased coaxial load. The measured load distributions indicated that the predominate anchoring force of cable bolts was the result of frictional resistance at the cable–grout interface and not dilational slip and shearing of grout flutes. Furthermore, this determined that a grouted length in excess of 2.5 m would be required to fail a typical 15.24 mm diameter cable with an unconstrained end (typical loading condition of tie-backs and toe-grouted cables bolts).

Keywords: cable bolt, fibre optic sensing, physical testing, pull test

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