Thermomechanical Effects of an Operating Geothermal Energy Pile on Adjacent Single-Row Piles: Field Test and FE Study

Geothermal energy piles combine the functions of load bearing and shallow geothermal energy utilization. When geothermal energy piles work together with adjacent nongeothermal energy piles, the mechanical behavior of the nongeothermal energy piles remains poorly understood. In this paper, a single-row pile group foundation is investigated, in which an operational geothermal energy pile is connected to several conventional piles through a cap beam. Field monitoring was conducted, and a two-dimensional thermomechanically coupled finite-element (FE) model was developed and validated against the measurements. We investigated the effects of pile spacing S, the relative stiffness of the cap beam Era, and the intermittency ratio n on the response of adjacent nongeothermal energy piles. The results showed that the mechanical response of adjacent piles caused by the geothermal energy pile is concentrated near the pile side and decays rapidly with increasing dimensionless spacing S/D. When S/D ≥ 8, the thermally induced stresses in the adjacent piles at the upper part of the cap beam at about 2S from the geothermal energy piles decay to about 10% of the peak value, and the pile–pile thermal interaction is acceptable for engineering practice. Increasing the cap beam stiffness amplifies the upper beam tensile stresses at geothermal energy piles, but the effect on nonadjacent piles is limited. The influence range and interaction threshold based on S/D are proposed, which can provide a reference for the spacing arrangement of geothermal energy piles in single-row pile group foundations and beam–pile coordination design.