PSI - Issue 64

Luca Schenato et al. / Procedia Structural Integrity 64 (2024) 1636–1641 Luca Schenato / Structural Integrity Procedia 00 (2019) 000 – 000

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3. Results To verify the persistence of the Rayleigh signature, independently from the interrogator and setup, we first applied the SCA method to measurements collected from fiber-equipped soil anchors installed at a landslide in Italy. The site is at Giucano landslide in the Lumigiana Valley (Fosdinovo, Tuscany, Italy). The landslide was initially triggered in May 2013 after heavy rainfall. It reactivated again in the spring of 2014, following another period of intense and prolonged rains. However, the subsequent years were relatively dry, and the movements ceased. The anchors were installed in the spring of 2018, and a set of reference traces was collected after the cement filing hardened. Then, the anchors were activated by pulling their heads against the concrete slabs, and the fibers in the anchors were monitored for some months. Cola et al. (2019) described and discussed the installation phase and first measurements. Then, the measurements were interrupted due to the impossibility of continuing to reference the initial traces with commercial software implementing the standard correlation. In particular, the original patch cord from the interrogator to the fibers got lost, one cable was respliced, and the interrogator was replaced. Nonetheless, the measurement campaign was successfully resumed in the summer of 2022, using the SCA method. Fig. 1 shows some of the results, including the strain from the last measurement and the preceding ones. The strain curves determined from the analysis performed on the last measurements are consistent with the evolution of the landslides. In particular, the strain curves of anchors 1 and 3 related to the previous measurement session continue to show marked peaks, 3 m spaced apart, corresponding with the nuts used to couple the bars that compose the anchors mechanically (left plot:  ,  and  right plot:  and  ). Furthermore, the deepest nut related peak in anchor 1 (  ), at approx. 8 m depth was absent in 2018, suggesting a significant progressive tension acting on that nut. The more recent strain curve at anchor 3 shows a relevant strain at 1.5 m depth, already present in older measurements. The same curve reveals the depth of the sliding surface at the bedrock interface, which was not so precisely and clearly identifiable from older measurements. The sliding surface can also be identified from the strain of the most recent measurement at anchor 1, yet less markedly than anchor 3. All these data unveil the landslide dynamic, which would not be revealed otherwise without the continuity in referencing the measurements provided by the SCA method.

Fig. 1. (a) Strain measured at smart soil anchor 1 in Oct. 2018 and Jul. 2022, and (b) at smart soil anchor 1.

These results clearly confirm the persistence of the Rayleigh signature: the more recent traces just needed to be appropriately correlated to the reference ones for the signature to be revealed. Additionally, we validated the methodology at another site: a steel-tied arch bridge built in 2016, part of a new local road called “Terraglio Est” in the Veneto region (Italy). Here, we instrumented a continuous fly auger (CFA) pile at its north abutment. Bersan et al. (2018) and Cola et al. (2019a) describe more details about installations and