Thermo-hydro-mechanical response of energy-piled walls under varying wall configurations, pipe layouts, and seepage conditions

Energy-piled walls combine earth-retaining and thermal energy-harvesting functions; however, their thermo-mechanical behaviour remains less understood than that of energy foundation piles. This study investigates the coupled thermo-hydro-mechanical response of energy-piled walls using 3D, time-dependent, coupled finite-element models over a six-month heating period, focusing on the effects of wall type, pipe layout, seepage, and thermo-induced pore water pressure. Key findings indicate that: (i) wall type and thermal boundaries influence lateral displacements, with magnitudes remaining below ±2mm under all conditions examined; (ii) the 4U-shaped pipe layout may be preferred over the spiral layout due to generally lower thermo-induced stresses; (iii) seepage enhances heat exchange capacity but introduces wall-slab-seepage interactions that invert bending moment distributions at excavation depth, with behaviour controlled by permeability thresholds ($$k \ge {9.09}\times {10}^{-13}{\textrm{m}}^{2}$$ for seepage-dominated; $$k < {9.09}\times ^{-17}{\textrm{m}}^{2}$$ for pore-pressure-dominated behaviour); (iv) peak tensile stresses can exceed concrete capacity, particularly at slab-pile connections, indicating potential localised cracking. The findings are synthesised into a conceptual framework that accounts for these coupled interactions and provides quantitative design guidance across diverse wall configurations, pipe layouts and ground conditions.