Analysis of energy pile groups subjected to non-uniform thermal loadings

Sequentially coupled thermal-stress finite element analyses were performed to investigate the mechanical behaviors of an energy pile group subjected to non-uniform thermal loadings. The group effect was highlighted by comparing the thermo-mechanical responses with those of the single pile case. Due to the thermal interactions between piles, the group piles’ temperatures were higher than that of the isolated single pile. If only part of the piles served as heat exchangers, i.e., the pile group was thermal loaded unevenly, there were differential deformations between the heated and the non-heated piles. Due to the pile-raft-pile interaction, the axial forces of the piles changed significantly. The location of the heated pile had an important influence on the thermally induced axial force, while the effect of the soil's coefficient of thermal expansion was not significant. Inspired by the numerical result, a simplified method was proposed to capture the main characteristics of energy pile groups and to facilitate the design. The proposed method was developed in the framework of the traditional load transfer approach, and the pile-raft-pile interaction was included. By applying different temperature increments to different piles, the non-uniform thermal loading was modeled. The proposed method was verified by comparing with the finite element analysis results and the data collected from the literature.