Numerical study of grout–rock mass interaction effect on distributed optical fibre sensor measurements

Authors: Madjdabadi, B; Valley, B; Dusseault, MB; Kaiser, PK

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DOI https://doi.org/10.36487/ACG_rep/1410_31_Madjdabadi

Cite As:
Madjdabadi, B, Valley, B, Dusseault, MB & Kaiser, PK 2014, 'Numerical study of grout–rock mass interaction effect on distributed optical fibre sensor measurements', in M Hudyma & Y Potvin (eds), Deep Mining 2014: Proceedings of the Seventh International Conference on Deep and High Stress Mining, Australian Centre for Geomechanics, Perth, pp. 457-468, https://doi.org/10.36487/ACG_rep/1410_31_Madjdabadi

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Abstract:
Distributed Brillouin sensing (DBS), used initially in structural health monitoring for bridges and pipelines, is attracting attention in the field of strain measurement in underground infrastructure, including mining. Strain measurements along an effectively unlimited lengthoffer opportunities to capture the deformation field induced by underground excavations beyond the excavation damaged zone (EDZ). The potential benefit of such mine-wide monitoring of the deformation field includes improved calibration of stress–strain deformation models. For underground mines a challenge for rock masses resides in borehole installations that can respond to mining. This response is partly as continuum deformation in extension, compression or shear, or as discontinuum deformation through localised shear or dilation of discontinuities. The objective of this paper is the optimisation of the installation scheme to ensure proper strain transfer to the measuring fibre while being able to accommodate and measure localised strains induced by discontinuities. To this end, a numerical study was conducted to evaluate the grout and grout–rock interface properties’ effects on the strain transfer process from rock mass to the cable. The grout stiffness was found to be the most influential parameter. Also, slippage along the rock–grout interface is not an issue for the strain transfer process since a deep environment provides a high confining stress on the borehole wall resulting in high shear strength at the interface.

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