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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3.2. Site B: DFOS installed in vertical borehole

Fig. 4b and 4c depict the temperature recorded by DTS during the peak of the flooding event along boreholes S2, S3, and S4, respectively positioned on the landside berm, on the embankment top, and on the riverside berm. Again, the temperature distribution shown in the graph is derived from linear interpolation of the measured data along the boreholes, considering the horizontal distance between the wells, which is approximately 10 m. On the countryside berm (above S2), the air temperature was specified, while on the Adige side, river temperature was assumed in the node wet by the river and air temperature in the other. In both cases the average temperature of the respective day was assigned, according with data recorder at the hydrometric station. The temperature distributions during the flood are here compared with the temperate distribution observed with DTS on September 27 th , 2022, (Fig. 4a) when the river water level was low and a pre-flooding temperature were recorded. It is noteworthy that normally the water table (WT) is at 6-7 m below the embankment crest (S3), thus about 3.5 m below the landside berm (S2). Consequently, during summer, solar radiation and air temperature influence the soil temperature above the WT, resulting in the highest temperatures by the end of summer (up to 25°C). In Autumn, as the air temperature decreases also the levee body cools down, as it is evident in Fig. 4a (max 18°C). During the flood event, due to rain water infiltration, the shallow soil layers on the landside and the upper part of the embankment rapidly saturated, leading to a reduction of approximately 3-6°C in soil temperature. The temperature decrease is stronger on the landside, while, the riverside cools down slowly, as evidenced in Fig. 2b by the transducer TT10, located at 3-4 m below the berm along the river. Noticed in Fig. 4b that a warm core persists during the event in the center of the levee body. Finally, in the last measurement, obtained after the rain subsided (Fig. 4c), the warm core appears to have cooled and extended towards the field side, influenced by a wedge of cooler water entering from the river and traveling along a sandy layer located approximately 10m below the embankment crest. No variations of temperature are observed below 12 m of depth from the embankment crest, indicating that deeper soils are almost not at all involved in water seepage or influenced by temperature variations in the river or outside the river.

Fig. 4. Temperature distribution obtained interpolating DTS measured along boreholes S2, S3 and S4 at: a) 27/09/2022 11.25 b) 31/10/2023 15.30; c) 03/11/2023 12.10. The comparison among temperatures measured by traditional transducers with those recorded by DTS reveals a general agreement in temperature trends. For instance, both systems show no temperature variations below 12 m of depth below the embankment crest. The TT10 sensor, situated on the river side berm at a depth of 3 m, recorded a temperature change of 1.4°C from October 31 to November 3, which is consistent with the DTS measurements obtained at the same position. Furthermore, even the smallest temperature variations near the TT2 (countryside berm)