Fibre optic sensing for strain field measurement in geotechnical laboratory experiments

Strain measurement inside the soil body in three-dimensional (3D) experiments is a real challenge for physical modellers in geotechnics. The use of fibre optic sensing offers the possibility of continuous measurement of the strain at depth with high spatial and temporal resolution in small-scale laboratory experiments. Despite the technology not being fully ready yet for centrifuge experiments, this is an important development in geotechnics. This paper explores the capacities of distributed fibre optic sensing (DFOS) as a solution for direct soil strain profile measurement at depth. A series of small-scale plane-strain experiments is used to simulate the simple case of the formation of a downwards subsidence. DFOS cables are laid in the soil specimen, and strains are directly compared with the soil movement, recorded with cameras through particle image velocimetry. Results indicate the ability of DFOS in detecting soil movements and underline the typical signature strain profile expected during this type of experiments. Finite-element analyses are carried out to further underpin the consequences of performing these tests at 1g and extend the findings to potential applications in 3D and on the geotechnical centrifuge. This shows promising results for detection of soil strain profiles inside the soil body in 3D.