Geohazards pose significant dangers to human safety, infrastructures, and the environment, highlighting the need for advanced monitoring techniques for early damage detection and structure management. The distributed optical fiber sensors (DFOS) are strain, temperature, and vibration monitoring tools characterized by minimal intrusiveness, accuracy, ease of deployment, and the ability to perform measurements with high spatial resolution. Although these sensors rely on well-established measurement techniques, available for over 40 years, their diffusion within monitoring and early warning systems is still limited, and there is a certain mistrust towards them. In this regard, based on several case studies, the implementation of DFOS for early warning of various geotechnical hazards, such as landslides, earthquakes and subsidence, is discussed, providing a comparative analysis of the typical advantages and limitations of the different systems. The results show that real-time monitoring systems based on well-established distributed fiber-optic sensing techniques are now mature enough to enable reliable and long-term geotechnical applications, identifying a market segment that is only minimally saturated by using other monitoring techniques. More challenging remains the application of the technique for vibration detection that still requires improved interrogation technologies and standardized practices before it can be used in large-scale, real-time early warning systems.

In northern Campania (Southern Italy), the historic center of many towns is characterized by the widespread presence of cavities in the subsoil, excavated over the centuries for quarrying tuff blocks for buildings, along with cathedrals, churches and chapels. A singular feature of these places of worship is, in fact, the presence of a wide and frequently connected network of underground cavities and tunnels, which were used for hydraulic, religious or connecting purposes. The cavity network is often unknown, abandoned or even buried, thus representing a risk for their susceptibility to sinkholes. Such elements are important as cultural heritage of inestimable value and as attractors for tourism; for this reason, the multidisciplinary study conducted on a place of worship in the Caserta area is illustrated herein: the Cloister of Sant’Agostino, in Caserta (XVI century CE). A geological and geotechnical characterization of the subsoil was performed at first. A laser scanner survey of the accessible cavities and the external churchyard was carried out. The resulting 3D model of the underground sector allowed for a clear understanding of the room size, their location, the levels and the path of the corridors. To understand the extension and layout of the crypts, Electrical Resistivity Tomography (ERT) surveys were undertaken in the surrounding areas. The analysis of the ERT measurements revealed some anomalies that could be ascribed to unknown structures (crypts). Finally, numerical methods were applied to estimate the stress state of the soft rocks and the potential areas of crisis, with preliminary assessments of the influence of the presence of cavities on the stability of the subsoil. The results allowed us to improve the knowledge of the study site and provide useful data for the planning of future targeted investigations, underlining how integrated research between applied disciplines can provide indispensable support both in the management and mitigation of geological risks in urban areas and in the sustainable reuse of hypogea.

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.

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.