Fiber optic based technology can be used as an unmatched tool for monitoring, detecting and analyzing the deformation in soil slopes or any type of ground movement during the pre-failure stage. It is crucial to monitor hazard-prone regions to save human lives and assets. The effectiveness and sensitivity of DFOS technology are promising for possible use as a reliable early warning and forecasting system. Also, it can play a crucial role in the construction and post-construction period of engineering projects such as tunnels, pipelines, bridges, or open road cuts.

Exploiting its high spatial detection range (up to 2 km of fiber length) the sensor cable can be deployed all across the potentially unstable areas even when their location is not known apriori, and to measure the displacement of the unstable soil mass with respect to the stable ground along the cable length. Thanks to its high sensitivity and spatial resolution, the sensor cable can detect and monitor the development of small strain within the ground movement.

Wires&Bytes offers a number of cables that serve for detection of slope or ground movements such as Non-metallic MultiSense, UniTEF, or CreepGuard.

MultiSense product fits well to this application as it combines strain-coupled and strain-free fiber configuration. Strain sensing fibers in the armor layer can be stranded to the customer specified helix lay-length, tuning the strain sensitivity of the cable and customizing it to a magnitude, exceeding the physical possibilities of uncabled optical fibers. For strain values beyond 1% we recommend considering the deployment of loose tubes in the armor layer. For all the other strain rates equal or lower than 0.15%, the central loose tube will be needed for temperature compensation or for organizing the loop for stimulated Brillouin scattering interrogation.

Further, its unique feature of pressure-strain transduction, MutiSense cable is acoustically very sensitive to pressure changes in the environment, in this case with the soil in which it is deployed. This feature needs only 1 single-mode fiber in the stranded layer, and it will provide even more useful data to a monitoring specialist and data analyst, which will be unprecedented and critical for future decisions. Both in the lab and in the industry MultiSense has been proven to exhibit high seismic sensitivity using standard telecommunication fibers only and this contributes to the cost efficiency in the projects. The sensitivity is comparable with Rayleigh backscatter enhanced optical fibers and it can be extensively used when the cable is deployed in the soil for various and independent data acquisition.

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Picture credit: Oregon Department of Transportation