Distributed optical fibre sensing for early detection of shallow landslides triggering

Abstract

A distributed optical fibre sensing system is used to measure landslide-induced strains on an optical fibre buried in a large scale physical model of a slope. The fibre sensing cable is deployed at the predefined failure surface and interrogated by means of optical frequency domain reflectometry. The strain evolution is measured with centimetre spatial resolution until the occurrence of the slope failure. Standard legacy sensors measuring soil moisture and pore water pressure are installed at different depths and positions along the slope for comparison and validation. The evolution of the strain field is related to landslide dynamics with unprecedented resolution and insight. In fact, the results of the experiment clearly identify several phases within the evolution of the landslide and show that optical fibres can detect precursory signs of failure well before the collapse, paving the way for the development of more effective early warning systems.

Toward Distributed Fiber‐Optic Sensing of Subsurface Deformation: A Theoretical Quantification of Ground‐Borehole‐Cable Interaction

“…These reference values may or may not be applicable to other DSS field experiments; the strain gradient range depends on geological contexts and deformation scenarios. For ground‐cable strain transfer analysis we consider a fixed‐point or microanchored design (Figure S1), which has become increasingly popular for DSS applications (Hauswirth et al, 2012; Iten et al, 2011; Picarelli et al, 2015; Schenato et al, 2017). We treat each cable section (separated by two neighboring anchor‐like elements) separately and assume an axially uniform strain field within each section.…”

“…The Young's modulus, E c , of a buffered cable may vary significantly depending on whether metal tubes, stranded stainless steel wires, or fiber‐reinforced polymers are employed. Generally though, E c between 0.3 and 75 GPa and r c between 0.45 and 4.5 mm were commonly reported (Iten et al, 2011; Lienhart, 2015; Schenato et al, 2017). Consequently, E c r c ranging from 0.3 to 120 MN/m is analyzed in the current investigation.…”

“…Since the cable can sense both tensile and compressive strains, by using equation 2 a continuous profile of ground deformation (rebound or compaction, or both) can be mapped. Further details of the DSS technology for deformation measurement may be found in Schenato et al (2017).…”

Vertically Distributed Sensing of Deformation Using Fiber Optic Sensing

“…DFOS with Raman scattering has already been known as distributed temperature sensing and utilized for a host of hydrological and geothermal applications (Briggs et al, 2012;Carlino et al, 2016;Curtis & Kyle, 2011;Selker et al, 2006). Recently, by exploiting changes in Brillouin and Rayleigh scattering induced by external strains, the DFOS technology has been utilized for geohazard sensing including earthquake observations (Dou et al, 2017;Jousset et al, 2018;Lindsey et al, 2017) and landslide detection (Huntley et al, 2014;Lienhart, 2015;Michlmayr et al, 2017;Picarelli et al, 2015;Schenato et al, 2017). While a few studies have explored the feasibility of DFOS for subsidence and strata deformation sensing (Murai et al, 2013;Wu et al, 2015), the understanding of data collected from borehole-embedded FO cables has remained elusive and hence precluded its use in many contexts.…”

Multi-source data assimilation for physically-based hydrological modeling of an experimental hillslope

“…A uniform 60 cm-thick silty fine sand was deployed on top of a relatively impermeable basement made of sandy clay soil. More details on the soil properties can be found in Lora et al (2016) and Schenato et al (2017). In the following, we will refer to the two soil types simply as sand and clay.…”