PSI - Issue 64

Lorenzo Brezzi et al. / Procedia Structural Integrity 64 (2024) 1589–1596 Author name / Structural Integrity Procedia 00 (2019) 000–000

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measurement can influence the interpretation of subsequent measurements. Moreover, this measurement is the first available for anchor A1 and allows for the evaluation of deformation evolution in the bar from the installation day. The next measurements campaign was performed on the 14/12/2023, resulting a second dataset for A1, and a first reading for A2, after 48 days from its installation. No measurements were possible on that date for A3. Finally, for anchorage A3 the reference reading was taken only in January 2024, after 83 days from the bar installation. Given the loop configuration of the cable, the strain field is probed twice at each depth and, in Fig. 5 and 6, the strains measured in both the ascending ( up-down ) and descending ( down-up ) cable sections are represented in the plot. The similar ascending and descending strain distributions testified that no relevant bending deformations are detectable. More relevant, but still small variations are observable in the vicinity of the anchor head, in the portion of the bar outside the soil, where effects such as temperature and deterioration of the cementitious mortar are non-negligible.

Inclinometer S5

Inclinometer S4

3.5 m 8.5 m 15.0 m Inclinometer S2

20

20

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8.0 m

4.0 m 18.5 m

2.0 m 10.0 m

8.0 m

4.0 m 18.5 m

1.5 m 10.0 m

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27/10/2023

27/10/2023

27/10/2023

18/01/2024

18/01/2024

18/01/2024

14/12/2023

14/12/2023

14/12/2023

05/10/2023

05/10/2023

05/10/2023

5

5

5

Displacements [cm]

Displacements [cm]

Displacements [cm]

c)

b)

a)

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Fig. 4. Displacements recorded by three continuous inclinometer monitoring systems, composed by sensors at different depth of (a) S2 unit, located close to A1; (b) S4 unit, located close to A2; (c) S5 unit, located close to A3. The depths of the sensor units are reported.

4. Discussion Some initial comments are possible about strain in anchor A1. Fig. 5a shows a distribution of traction strains along the entire bar of around 200 μ ε . The slight level of deformation is probably due to two different effects: in the external 15 m of bar the strain is induced by the installation of the concrete plate, in November 2023, that was slightly pushed against the slope, creating a traction effect on the anchor. At the same time, a slight activation of the reinforcement can be detected in the last 10 m of bar, probably due to some slope movements. This interpretation is confirmed looking at Fig. 5b, where the measurements are reported with respect to the reference reading of December 2023. Some relaxing is detectable in the external 15 m of bar, with a strain that is decreasing in time. No variation is visible instead in the deeper portion of reinforcement. In any case, the level of strain is quite small and it is indicating that the anchor is still almost inactivated. The slope displacements, as visible in Fig. 4a, were almost negligible, confirming a temporary stability of the slope and the effectiveness of the engineering solutions applied. The outer 5 meters of strain exhibit less regularity, attributable to both shallow slope instability and significant temperature variability. As previously noted, temperature compensation was not feasible in the presented graphs. Additionally, regarding Fig. 5, as already mentioned, it is important to consider the selection of reference measurements. While both graphs depict the same measurements, their shapes differ noticeably, leading to varied interpretations. In particular, without the graph in Fig. 5a, the strain trend visible in Fig. 5b would not be immediately interpretable, with the bar seemingly experiencing increasing compression (negative strain). In reality, as noted, this effect is due to a reduction in tension compared to the initial condition and does not correspond to true compression of the bar. Looking at Fig. 6a, the strain behaviour of the external 15 m of bar is similar to what commented of Fig. 5b. Some slight activation can be distinguished in the deeper 10 m of anchor. In this case no reference reading is available related to the date of bar installation (27/10/2023), the first reading was possible only on 14 December 2023.