Water Loss (WL) is a global issue. In Italy, for instance, WL reached 36.2% of the total fresh water conveyed in 2020. The maintenance of a water supply system is a strategic task that requires a huge amount of investment every year. In this work, we focused on the use of Distributed Fiber Optic Sensors (DFOS) based on Stimulated Brillouin Scattering (SBS) technology for monitoring water pipeline networks. We worked on High-Density Polyethylene (HDPE) pipes, today the most widely used for creating water pipelines. By winding and fixing the optic fiber cable on the pipe’s external surface, we verified the ability to detect strain related to pressure anomalies along a pipeline, e.g., those caused by water leakage. We performed two experimental phases. In the first one, we assessed the sensibility of sensor layout on an HDPE pipeline solicited with static pressure. We investigated the viscoelastic rheology of the material by calibrating and validating the parameters of a Burger model, in which Maxwell and Kelvin-Voigt models are connected in series. In the second experimental phase, instead, we focused on the detection of the pressure anomaly produced by leakage in a pipeline circuit set up with running water moved by a pump. The theoretical and experimental studies performed returned overall positive feedback on the use of DFOS for the monitoring of HDPE water pipelines. Future developments will be focused on more detailed studies of this monitoring solution and on the industrial production of “natively smart” HDPE pipes in which DFOS cables are integrated into the pipeline surface during the extrusion process.

We present a case study of a Structural Health Monitoring (SHM) hybrid system based on Brillouin Distributed Fiber Optic Sensors (D-FOS), Vibrating Wire (VW) extensometers and temperature probes for an existing historical water penstock bridge positioned in a mountain valley in Valle d’Aosta Region, Northwestern Italy. We assessed Brillouin D-FOS performances for this kind of infrastructure, characterized by a complex structural layout and located in a harsh environment. A comparison with the more traditional strain monitoring technology offered by VW strain gauges was performed. The D-FOS strain cable has been bonded to the concrete members using a polyurethane-base adhesive, ensuring a rigid strain transfer. The raw data from all sensors are interpolated on a unique general timestamp with hourly resolution. Strain data from D-FOS and VW strain gauges are then corrected from temperature effects and compared. Considering the inherent differences between the two monitoring technologies, results show a good overall matching between strain time series collected by D-FOS and VW sensors. Brillouin D-FOS proves to be a good solution in terms of performance and economic investment for SHM systems on complex infrastructures such as hydropower plants, which involve extensive geometry combined with the need for detailed and continuous strain monitoring.

The problem of levee embankment control during high flows is crucial for flood risk management in floodplains. Levee defense lines are often hundreds of kilometers long and surveys during emergencies are not easy tasks. For these reasons, levees monitored with in situ sensors and a suitable Information Technology (IT) real-time data communication and integration infrastructure, so-called “smart levees”, are gaining increasing interest as a crucial protection technology in floodplains. The paper presents the conceptualization of a prototype of a levee smart revetment, based on the integration of an optical fiber (OF) cable into a steel double-twisted wire mesh. In this paper the feasibility of this kind of revetment is firstly assessed. The flow pattern of overtopping water on the embankment is discussed, thus producing a raw estimation of the shear stress acting on the revetment in the field. A sample case is then analyzed in both numerical and laboratory tests. For this purpose, a numerical Finite Element Model (FEM) to describe the mechanical behavior of a double-twisted wire mesh when loaded along its own plane is presented. Numerical results indicate that the related strain, relatively low as compared to the steel wire yield stress, can be fully detected by the optical fiber continuous Brillouin sensor. This has been validated by the experimental activity performed and a digital twin of the prototype of the smart revetment, suitable for virtually testing the product under any load and constraint conditions and tailoring the production process, has been created.

The ubiquitous optical fiber infrastructure already installed for telecommunications purposes represents a precious asset for pervasive sensing. The telecom fiber plan can be used not only for controlling the network integrity itself, but also for monitoring the road traffic, for large breaches and damages detection in civil structures, for the supervision of utilities health, and for the prompt detection of seismic and natural hazards. Nowadays, systems based on distributed acoustic sensing (DAS) are successfully applied also in telecom links, to provide measurements with very high resolution and spatial accuracy in localization. In particular, DAS systems appear very attractive to operate as fiber seismometers for early earthquake detection. However, DAS back-scattering approach requires complex and expensive DSP and storage of a huge amount of data, not generally compatible with the budget of large-scale sensing applications. Interferometric solutions constitute a possible alternative, but usually they employ ultra-stable laser sources, characterized by laser coherence length longer than the sensing fiber to monitor. For extensive applications of optical sensing in the pervasive fiber telecom infrastructure, sustainable in terms of cost, energy efficiency and reliability, we propose to adopt the interferometric approach, but constructing the interferometer itself directly embedded inside the multi-fiber telecom cable, where two fiber operate as interferometric arms. No stringent requirement is necessary for the laser sources and typical telecom DFB lasers are employed together with a simple detection scheme. In this paper we show how the proposed “in-cable” sensor is used over the deployed telecom network to monitor geo-hazards. In particular, its operation to detect risks of landside affecting the safety of a railway in the north side of the Lake Iseo, Lombardia is presented. Two standard single-mode fibers of the 48-fiber telecom cable installed in a conduit under the sidewalk running alongside the railroad tracks by an Italian operator are employed to realize the sensor. Not only traffic events such as travelling trains, car passages on a railroad crossings and pedestrians crossing the track are detected, but above all the fall of rocks obstructing the tracks are identified. Suitable machine-learning allows to classify and discriminate dangerous events for the safety of the railway from nuisances caused by the noisy and hostile environment, that can be sources of annoying false alarms. Providing integral measurements, this interferometric sensor does not localize the event, but gives early warning of possible risks for the railway, detecting in real time landslides and notifying the alarm in a proactive way. Other applications related to the monitoring of tunnels and viaducts, river embankments and shallow landslides triggered by rainfalls are also demonstrated. This work was partially supported by the Italian Government through project PRIN 2022 SURENET and by the European Union under the Italian National Recovery and Resilience Plan (NRRP) of NextGeneration EU, partnership on “Telecommunications of the Future” (PE00000001 - program “RESTART”) in the project SENSING NET.