Applicability of an interferometric optical fibre sensor for shallow landslide monitoring – Experimental tests

Optical fibre-based sensors have found a variety of applications throughout engineering and science in the measurement of strain and temperature. Current commercially available sensing technologies are able to provide strain measurements in the order of microstrain across tens of kilometres of range. The strong demand for reliable sensing tools in engineering geology allowed for the advancement of the optical fibre technology which has settled in this field during the past decade. Among the variety of sensing approaches, interferometric fibre optic sensors have rarely been tested for detection of ground movement. In this work we present the results of six laboratory scale experiments in which simulated rainfall induced shallow landslide model made up of non-cohesive soil is equipped with a newly developed coherent fibre optic sensor. Results indicate that a phase of early precursors of instability could be identified by the sensors in all six experiments, two to eight minutes before slope failure. The sensing system proved to be reliable in detecting the evolution of slope stability at shallow depths of up to a few meters depending on the sensors' burial depth, hence stating the emergence of a simple and cost-effective approach for detailed strain monitoring. The proposed sensing technique could therefore provide a viable and cheaper alternative to commercially available optical fibre interrogators and furnish quantitative monitoring data for shallow landslide monitoring in soil-like materials. In order to be efficient for the detection of such failures with a significant precursory window, sensors should ideally be placed in the vicinity of a sliding surface or landslide boundary, which is an achievable task given the high sensing range and multiplexing capabilities of optical fibre sensors.