New Smart Extenso-Inclinometer for monitoring slow moving landslides

Landslides are a serious hazard globally and the exposed areas require a strong effort for their surveillance and protection of populations and infrastructures at risk. When the volumes involved in complex gravity-driven processes are enormous, it would be difficult or impossible to implement active works for landslide hazard mitigation. Therefore, a better understanding of the underlying processes is necessary. A possible way to go forward is to implement a monitoring system in an affected area which allows to observe possible accelerations of the movement in order to implement appropriate mitigation strategies. In active slow landslides, inclinometer monitoring is a valuable resource despite its limitations, such as low spatial resolution, time-consuming activities, unserviceability in case of high deformation of the inclinometer casing.

To overcome these challenges, a new Smart Extenso-Inclinometer (SEI) has been developed. This instrument is realized by disposing of four patented NSHT (New Smart Hybrid Transducers) transducers, based on fiber-optic sensing technology, on the outer surface of an inclinometer casing, enabling traditional measurements to be conducted simultaneously. The adopted sensing technique is based on the stimulated Brillouin scattering phenomena which allows detection of strain and temperature changes along the NSHT with a spatial resolution up to 20cm.

To test the effectiveness of the new device in different contexts and conduct an in-depth investigation of the landslide mechanics, some SEIs were installed at the study area of Centola (Italy) and at the Brandstatt landslide observatory in Lower Austria (NE Austria). In the first site, an active landslide system involves a layer of landslide debris and a conglomeratic formation which extensively outcrops above the marl-clayey Mesozoic formation. Here, n.2 SEIs have been installed to couple manual inclinometric measures. The Austrian study area represents a good example of a potentially deep-seated, complex slow-moving earth slides system that involves clay-rich lithological formations and deeply weathered materials. This slope exhibits surface geomormological features often indicative of continuous, slow landslide activity, which is also shown by traditional inclinometer measurements in selected locations across the slope. Here, n.1 SEI has been installed in an inclinometer casing in the most active sector of the slope instability.

The first monitoring results show that the strain profiles obtained with the innovative instrument are consistent with the inclinometer data in revealing the main characteristics of both monitored slope movements. Moreover, the use of SEI added information not recognizable with the conventional inclinometer, as it revealed not only the horizontal but also the vertical component of soil strain, so acting like a distributed extenso-inclinometer. This is particularly important in scenarios such as the one of Centola , where the displacement components in horizontal and vertical directions are of the same order of magnitude.

The ongoing research activity demonstrates the effectiveness of the SEIs, highlighting the advantages of distributed soil strain detection compared to traditional displacement measurement techniques, for accurate and long-term monitoring of complex landslides.