PSI - Issue 62

Luca Comegna et al. / Procedia Structural Integrity 62 (2024) 484–491 Luca Comegna/ Structural Integrity Procedia 00 (2019) 000 – 000

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on both the previously described litostratigraphic units (Fig. 2a): the upslope part directly rests on the tectonised parent formation, while the downslope part lies on the debris cover.

Table 1. Monitoring campaigns carried out from 1998 to 2019.

Investigation campaign

Depth [m]

Pressuremeter test

Borehole

Inclinometer Piezometer SPT

Sampling

G1 G2 P1 P2 G3 G4 G5 G6 G7 G8 P3 G9

20 15 20 12 25 25 25 35 35 40 20 40 40 38 20 20

x x

x

1998-2003

x x

x x x x x x

2006

x

x x

2015

x

x x

x x

x x

G10 G11 G12

2019

P4

x

The results of four investigation campaigns started between 1998 and 2019 (Fig. 1b, Tab. 1) provided information about the physical and mechanical properties of the involved soils, the displacement and the piezometric regime (Comegna et al., 2021; Comegna et al., 2022). In particular, a total of 16 boreholes were drilled, allowing for the installation of inclinometers and piezometers, the execution of Standard Penetration Tests (SPT), and pressuremeter tests, as well as the collection of undisturbed soil samples. About the embankment, it is an alternation of medium dense to dense layers of silty-sandy gravels and silty sands. The SPT allowed, in particular, to estimate a Young’s modulus E = 40 MPa, and a friction angle φ’ = 35°. Regarding the parent formation, it is a saturated clayey and gravelly silt with sand, including some blocks (as typical of flysch) featured by an overall low Plasticity Index IP = 6%, a quite high consistency index Ic = 2.34 and an average saturated hydraulic conductivity k sat = 2.0E-10 m/s. Regarding the strength parameters, a cohesion c’ = 14 kPa and a friction angle φ’ = 37° have been obtained after some triaxial compression tests carried out in drained and undrained conditions on undisturbed probes. A quite high average residual friction angle φ’ res = 20.4°, consistent with the low Plasticity Index of the soil, has been returned by the results of some direct shear tests. Moreover, an average Young ’s modulus E = 200 MPa has been estimated through the pressuremeter tests carried out until the depth of 27 m. Concerning the debris cover, in situ direct observations allowed the identification of a weathered gravel mixed with highly altered silty sand, but no further data about the corresponding physical or mechanical properties were unfortunately available.