PSI - Issue 84

Arianna Lupattelli et al. / Procedia Structural Integrity 84 (2026) 845–851

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equal to four times the pile diameter (i.e., 0.80 m). In the 2D plane-strain formulation, the out-of-plane rows of micropiles were idealized as continuous linear (wall-type) elements with equivalent stiffness properties per meter length in the out-of-plane direction (i.e., 25 m). The bottom and later boundary of the soil domain have been placed at a depth of 50 m from the ground surface, and at 25 m from the slab lateral edges, respectively (Fig. 1). The 2D numerical model uses a differentiated mesh: quadrilateral elements for the elongated micropiles, and triangular elements for the superstructure and soil for greater flexibility.

P1

P6

Fig. 1. View of the 2D numerical model implemented in COMSOL Multiphysics, and zoom of the energy-micropiled foundation.

The coupled thermo-mechanical problem involves heat transfer, mass transfer, and deformation phenomena, which are numerically solved in a time-dependent framework. The equilibrium and energy equations for the porous medium are as follows in Eq. 2 (Lewis & Schrefler, 1998): ⋅ + =0 (2) where ∇ denotes the divergence, σ ij the stress tensor, ρ the bulk density of the porous material, and g i is the gravity vector. The heat transfer mode considered is conduction, described by Eq. 3: − ⋅ ( ) = 0 (3) where T is temperature, ρC p and λ are the volumetric heat capacity at constant pressure and thermal conductivity, respectively. Both the micropiled foundation and the soil are modeled as linear elastic materials. For the purposes of the study, a previously well-characterized soil is selected. Accordingly, the soil profile is assumed to be uniform, consisting of a homogeneous layer of Beauchamp sand (Rotta Loria, 2021), fully saturated, with the equivalent thermo-physical properties of the fluid and solid phases. The foundation is made of concrete, and the micropile stiffness is calculated using a composite section with a 140 mm diameter steel tube of 10 mm thickness (Lupattelli et al., 2023a) along the full length, combined with grout assumed to have a stiffness of 12 GPa (Naus, 2010); the adopted properties are summarized in Table 1.