PSI - Issue 64

Nicola Fabbian et al. / Procedia Structural Integrity 64 (2024) 1649–1656 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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B. In order to characterize the seepage regimes, an extensive array of monitoring devices was deployed in each borehole, which complains: two pressure (TP) and temperature (TT) transducers, characterized by a precision of 2 kPa and 0.1°C, respectively; a DTS cable for precisely measuring temperature variations throughout the borehole profile; an electrical cable for performing 3D Electrical Resistivity Tomographies (ERT) in cross-hole and time-lapse modalities (beyond the scope of this paper). In each well, the DTS cable is vertically installed in a U-loop configuration and anchored to a pipe like support: after installation, the cable ends are splice together creating a unique optical cable crossing all wells and centrally interrogated. A detailed geotechnical characterization, installation methodology and cable type description are provided in Fabbian et al. (2024). In both test sites the DTS, composed by two multimode fibers, are interrogated according the Raman approach with a Sensornet's Oryx SR DTS. Upon proper calibration with a thermal bath, as described in Schenato et al. (2022), the DTS provides temperature data with a spatial resolution of 2 m and a precision of 0.1°C. The installed DTS comprises a hybrid cable embedding optical fibers and copper wires, enabling its utilization in both passive gradient and active heat pulse methods. This paper deals only with data obtained with passive gradient method. Before this study, only one flood event for each site had been analyzed. To draw more robust conclusions, it is Between October 30 th and November 3 rd , 2023, two consecutive significant floods affected the Adige River and its levee system. These occurrences provided another opportunity to assess the reliability of the monitoring system. Fig. 2 illustrates the pressures (a) and temperatures (b) recorded by transducers positioned at site B during the event, comparing with the same parameters captured by the hydrometric station situated on the left embankment. The initial flood led to a 4.5m surge in the river water level (RWL) within a 12-hour period, maintaining a safety margin of 1.1m below the crest of the levee. In the vicinity of site B, several springs, characterized by a medium discharge of clear water, manifested on the landside just close the levee toe. Conversely, in the central section at site A, there are 3 localized springs exhibiting higher flow rates and a slight transport of fine materials, so they required containment using sandbags. The subsequent flood peak occurred three days later (November 3 rd , 2023), reaching an RWL peak 1.5 m below the first flood. Despite this, the springs remained active also during the second flood peak, albeit with significantly lower intensity. deemed necessary to analyze additional flood events. 3. Observation during the floods of autumn 2023

Fig. 2. Total heads (a) and temperatures (b) registered by transducers on site B during the 2023 flood event (29 October 2023 – 6 November 2023).