Performance and Reliability of a Fiber-Optic Smart Extenso-Inclinometer for Long-Term Landslide Monitoring

Landslides represent a major natural hazard worldwide, particularly in areas characterized by complex geological settings. In many cases, especially where large volumes are involved or where rapid evolution is possible, conventional mitigation measures prove ineffective. Consequently, landslide risk reduction increasingly relies on the development of monitoring-based Early Warning Systems (EWS), capable of detecting precursory deformation phases prior to failure.

This research focuses on the application of distributed fiber-optic sensing technologies for landslide monitoring, with the long-term objective of improving predictive capabilities for both slow-moving and potentially rapid landslide phenomena. In perspective, this monitoring approach shows strong potential for early warning applications in rapid landslides, particularly in pyroclastic soils, where static liquefaction processes may develop and trigger very fast kinematics evolving into destructive mudflows with catastrophic consequences, including loss of life. However, full-scale experimentation on rapid landslides is extremely difficult to pursue, as it would require dedicated pilot sites and the occurrence of rare, rapidly evolving failure events, whose initiation mechanisms are often hard to capture in real time.

For this reason, the technology is currently being tested and evaluated in slow-moving landslide settings, which allow controlled long-term monitoring of deformation processes. In this context, a Smart Extenso-Inclinometer (SEI), based on distributed fiber-optic sensing and stimulated Brillouin scattering technique, has been tested. The system enables continuous soil strain measurements with centimetric spatial resolution, providing both horizontal and vertical strain components and overcoming several limitations of conventional inclinometer techniques.

Field monitoring activities have been carried out in Italy (Centola) and at the Brandstatt landslide observatory (Lower Austria). Although characterized by slow-moving kinematics, the Brandstatt site represents a key test case, as it exhibits higher deformation rates (in the order of cm/year) compared to others slow-moving landslides commonly monitored in Italy. Moreover, it offers a unique opportunity to assess the long-term performance, reliability, and maximum deformation capacity of fiber-optic sensors under conditions where traditional instrumentation has become unserviceable due to excessive deformation.

Preliminary results demonstrate that distributed fiber-optic measurements are consistent with conventional data while providing additional insight into complex deformation mechanisms, including both horizontal and vertical strain components. These findings support the potential of fiber-optic monitoring as a valuable tool for detecting precursory deformation processes and for bridging the gap between slow-moving landslide monitoring and early warning strategies for rapid slope failures.