DFOS-based inclinometers: challenges and potentialities in monitoring slow landslides

Abstract

In recent decades slope engineering greatly benefited from the use of optical fiber sensing technology which offers a few advantages over conventional landslide monitoring approaches, including distributed measurements over long distances, and remote, real-time monitoring. Among various uses of Distributed Fiber Optical Sensors (DFOS) in the geotechnical field, the one related to the setting up of a smart inclinometer for monitoring slow landslides interacting with structures and infrastructures seems to be the most interesting and advanced for its usefulness in the detection of soil deformation and, in perspective, for implementation in Landslides Early Warning Systems. However, there is still the need to face technical and interpretation issues. In this regard, starting from the data collected for two years in a complex gravitative landslide, where both conventional and DFOS-based inclinometers were installed, the constraints and potentiality of the new inclinometer are highlighted. The tested Smart Inclinometer, adopting a sensing technique based on the Brillouin scattering phenomena, revealed its capability to capture the main features of the landslide phenomena while revealing that, when the entity of both vertical and horizontal strain components is comparable, an accurate analysis is required to compensate for the thermal effect and the vertical soil deformation along the depth. After compensation, the data monitored with the new DFOS-Inclinometer is consistent with the results of the traditional inclinometer, demonstrating its reliability and feasibility. Moreover, the novel device, returning both the strain components, can serve also as a series of multi-extensometers of very high spatial resolution in turn demonstrating the advantage of DFOS-based inclinometers over conventional displacement measuring techniques.