PSI - Issue 84

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

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volume, P1 maintains more favorable thermal gradients. In contrast, P6 experiences faster soil overcooling due to limited thermal availability, leading to a rapid decrease in heat exchange and a near cessation of thermal transfer after 3–4 days, when the pile–soil interface temperature approaches that of the circulating fluid. After determining the heat fluxes of the two reference energy micropiles under snow-melting condition, the study evaluates whether an idealized viaduct abutment supported by energy micropiles can satisfy the thermal demand required for pavement heating using Eq. (1). Assuming a reference paved surface of 100 m² and a snow-free area ratio of A r = 0.5, the thermal energy required to melt a portion of the pavement was determined. Finite element simulations calculated the local heat flux (W/m²) for P1 and P6.

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Fig. 3. (a) total thermal power provided by edge micropile P1 (black line) and the central micropile P6 (grey line) of the foundation over 7 days of operation in snow-melting mode; (b) comparison between the energy demand as a function of A r and the total thermal power supplied by the energy foundation. The thermal power of a single micropile (Fig. 3a) was obtained by multiplying the local flux by its effective length, and the total foundation power was scaled to the full width (25 m) to convert 2D results into an equivalent 3D output. The results (Fig. 3b) show that the system supplies more power than needed during the first two days but fails to meet demand in the subsequent days up to the end of the 7-day period. This indicates that continuous operation leads to a progressive reduction in thermal output, so periodic pauses or thermal recovery cycles (Lupattelli & Salciarini, 2025) are important for maintaining long-term efficiency. 4.2. Thermo-mechanical behavior The following graphs of Fig. 4a-b provide a depiction of the temporal evolution of stresses and settlements as a function of depth for the two micropiles, P1 (in black) and P6 (in grey), when the geothermal system is subjected to thermo-mechanical loads. The results show that the Peak tensile stress occurs on day one of snow-melting, especially in P6 due to stronger cooling and nearby piles; P1 experiences less stress. Afterward, stresses become compressive (- 20 kPa at the tip to -100 kPa near the head). Thermal contraction causes minor tensile stresses, but the steel tube carries tension and concrete handles compression. Micropile heads are restrained, settling about - 4.5 mm; at 2 m depth, thermal effects add 2– 3 mm, while pile tips settle less. Peak cooling initially lifts 2 m depth by 5 mm, later stabilizing around - 5 mm .