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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Keywords: Geotechnical Investigation; Levee Monitoring; DTS Applications; Seepage; Real scale test.

1. Introduction Understanding and monitoring the structural integrity of levees present significant challenges due to their extensive length and the spatial variability of the soils forming both the embankment body and its foundation. This variability is especially pronounced in mountainous environments and areas with ancient paleo-beds. Monitoring systems play a pivotal role in this context by identifying areas susceptible to significant seepage and potential weak points prone to failure (Radzicki et al. 2021). Recent studies have highlighted temperature as a reliable indicator of seepage within levee structures and their foundations (Bersan et al. 2018; Cheng et al. 2021; Abbasimaedeh et al. 2021; Li et al. 2022; Dalla Santa et al. 2023). Temperature changes under regular flow conditions are primarily influenced by seasonal heat transfer from air to soil. However, during unusual seepage movements, significant water movement from upstream sources could causes notable temperature fluctuations. This indicates that substantial leakage can lead to temperature changes, signaling preferred flow paths, cracks, voids, permeable sections, and potential internal erosion. Integration of traditional field monitoring with distributed temperature sensors (DTS) for detecting and monitoring temperature variations emerges as a compelling approach. Two methods can be adopted to detect seepage by DTS: the passive gradient method and the active heat pulse method. The first one relies on observation of temperature alterations within the levee due to the seepage but requires temperature gradients. Conversely, the active heat pulse method involves hybrid sensor cables integrating optical fiber and copper wire. By briefly heating the sensor cable it is possible to detect areas with heightened water saturation or flowing regions which exhibit higher thermal transfer and more rapid cooling down. DFOS, renowned for its high spatial accuracy and continuous monitoring capabilities, is particularly adept at monitoring extensive structures (e.g., Zhou et al. 2022; Brezzi et al. 2023; Hottges et al. 2023). Despite its prevalence in various engineering applications and dam monitoring (e.g., Bekele et al. 2023), its application in monitoring river levees remains relatively limited due to a scarcity of published experiences in real-scale condition and the interpretation of measurement results. DFOS installations play a crucial role and are feasible in both new and existing embankments (Schenato 2017; Rabaiotti et al. 2023). In the latter scenario, cables can be buried using various methods, such as horizontal trenches or vertical boreholes. Given the potential applicability, both possibilities were tested by the authors at real-scale sites and presented in Fabbian et al. (2024) and Cola et al. (2021). Both installation methodologies present advantages and disadvantages; therefore, to draw accurate conclusions, it is necessary to proceed with multiple measurement campaigns at different hydraulic levels and river temperatures. This paper presents the application of DTS in two different configurations within the Adige River levee and discusses the The Adige Valley in Northern Italy has a history marked by significant floods, starting from the catastrophic embankment collapses of 1882, which resulted in the failure of ten distinct sections, the events in 1966 causing the entirely submerging of Trento, and, finally, the collapse of levees near Salorno in 1981 (Amabile et al. 2020; Zwanenburg et al. 2018). Following these events, the Mountain Water Authority of Bolzano Province undertook an intensive program for the “structural health” evaluation of Adige levees, promoting investigation and monitoring activities, but also experimental studies and modelling of the levee response. The current course of the river is the results of anthropogenic interventions undertaken in the late 19th century, primarily involving the construction of linear embankments to channel and straighten the river bed. The new levee system often intersects with the old course, and past levee collapses often occurred at these intersections. The proximity to the highway and railway, parallelly running to the levee, amplifies the potential risk of a collapse in terms of impact on people and economy. Given this context, this study focused on two test sites situated along the right levee embankment close to the village of Salorno (Fig. 1). The first site was realized in 2016 and considers a stretch of 350m where moderate piping phenomena were previously observed. To address this issue, a 10m-deep jet-grouting seepage cutoff wall was constructed in the late measures obtained in these two installations during a flood event occurred in autumn 2023. 2. Real-World Applications of Monitoring Technologies on Adige River Levees