Numerical investigation of fibre optic sensing for sinkhole detection

This paper forms part of the SINEW project (SINkhole Early Warning) and continues the work from Möller et al. (2022), where 1g experiments demonstrate the feasibility of using Distributed Fibre Optic Sensing (DFOS) for sinkhole early warning. This experimental campaign highlighted an order of magnitude difference in the strain between the soil and the cable that remains unexplained and weakens the confidence in the technology and/or the experimental method. This paper uses 3D finite element analyses to further examine this discrepancy and the soil-cable interface. The results further support the experimental findings and demonstrate that the DFOS signature strain profile is induced by the horizontal movement of the ground, and enhanced when sufficient coupling at the soil-cable interface is achieved. This result holds when modelling is scaled to realistic confining pressure and its significance is twofold. First, this needs to be accounted for in the DFOS laying technique. Second, particles of cohesionless soils undergo relatively high horizontal displacement away from the centre of the sinkhole, and this means that DFOS cables are able to detect subsidence away from the centre of the sinkhole. The paper illustrate this result and the signature strain profile expected in this case.