Distributed fibre optic sensing for sinkhole early warning: experimental study

This paper presents experimental work aimed at proving the feasibility of using Distributed Fibre Optic Sensing (DFOS) as an early warning system for sinkhole detection. 1g experiments were conducted using a plane strain trapdoor and scaled to provide insight into the formation of a sinkhole in sand, in which DFOS cables are laid at selected depths. The DFOS data are compared with the geomechanics of the soil displacement, recorded using Particle Image Velocimetry (PIV). It was demonstrated that the DFOS exhibits a signature strain profile at the location of the sinkhole, allowing a sinkhole to be located using the DFOS data. Differences in the PIV and DFOS data are however apparent, notably the strain magnitudes. Nonetheless, it is possible to estimate the size and location of the sinkhole at depth using the DFOS data. Using a preliminary study of the development of the zone of subsidence, for a range of relative densities, it is then possible to predict the extent of the damage zone at ground surface. Such results show the potential for the incorporation of DFOS in the construction of critical infrastructure to enable early detection of sinkhole formation and thus opportunity for remedial action to prevent catastrophic failures.