PSI - Issue 84

Alice Vitaletti et al. / Procedia Structural Integrity 84 (2026) 191–198

194

3.1. FEM modelling A three-dimensional numerical model was developed in Plaxis 3D to simulate the rotational sliding mechanism of the mapped landslide, which extends approximately 80 x 175 m, with a maximum sliding surface depth of 15 m (Fig. 2a). The model comprises three distinct soil regions: stable soil, landslide volume, and sliding surface (Fig. 2b), all defined using the Hardening Soil (HS) constitutive model (Schanz et al. 1999). A coarse-grained soil type was assigned based on the available geological information for the study area. In the absence of site-specific investigation data, the soil was assumed to be homogeneous, with identical physical and mechanical properties attributed to both the stable soil and the altered surface, except for the strength parameters. These values were calibrated through a sensitivity study based on back-analysis, in which cohesion (c’) and friction angle ( φ ’) for both the stable soil and the landslide volume were varied independently within ranges reported in the literature (Duncan & Wright 2005). The stiffness parameters were selected according to typical values for coarse grained soils (Brinkgreve et al. 2024). Specifically, the secant stiffness modulus ( 5 0 ) was set to 30.00 ∙ 10³ kN/m², while the tangentstiffness ( ) and the unloading/reloading stiffness ( ) were derived using empirical equations, resulting in values of 36.01 ∙ 10³ kN/m² and 110.80 ∙ 10³ kN/m², respectively. The same values were assigned to the sliding surface, while strength parameters were reduced to represent residual conditions. Table 1 summarises the assumed strength parameters for the three soil regions defined in the numerical model.

a

b

c

Fig. 2. (a) FEM model, including the soil volume and the bridge structure (numbers 1-3 refer to the bridge piers) . (b) Section plane π of the 3D model. (c) Bridge foundation structure.

Table 1. Strength parameters assumed for different soil regions.

Parameter

Stable soil Landslide volume Sliding surface Unit

Cohesion (c’)

35

25 28

5

kN/m 2

Friction angle ( φ ’) 35

26

°

The bridge interacting with the landslide is included in the numerical model and consists of six spans with a deck length of 243 m. Since the aim of the study was to evaluate the effect of the landslide on the foundations, specific simplifications were introduced for the superstructure. The piers were modelled as linear-elastic beams, and the deck as a single beam with a simply supported scheme. The foundation system comprises six reinforced-concrete piles, each 1 m in diameter and embedded to a depth of 20 m, connected by an 0.8 m thick footing slab (Fig. 2c). The groundwater level was assumed at a depth of 7.5 m below ground surface, approximately midway through the sliding surface, to account for pore water pressure effects on slope stability and the structural response.