A comparison study on the long-term thermomechanical performance of energy piles under three climatic conditions

Abstract

Energy piles provide a profitable solution for both structural support and space cooling and heating of residential and commercial buildings. Nevertheless, very few details have been reported on the long-term thermomechanical performance of energy piles concerning the influence of climatic conditions. In this paper, a numerical study is performed to elucidate the long-term thermomechanical behaviour of energy piles under three typical climatic conditions by considering thermal demands of a reference office building. Pile and soil temperature fluctuations, thermal pile axial force, and thermally induced pile head displacement are determined and compared. The results show that the surrounding soil thermal imbalance under climatic conditions with nonsymmetrical thermal demands is more significant than that under climatic conditions with balanced thermal demands. Moreover, notably lower thermal axial forces are induced at the end of thermal cycles under climatic conditions with nonsymmetrical thermal demands. However, the thermally induced pile head displacements are much larger under such climatic conditions, and longer thermal operations are needed to reach the steady state. The study suggests that the use of the unified design method of energy piles subjected to different climatic conditions may adversely affect the design effect. Besides, compared with the thermal forces, energy pile design should pay more attention to the adverse effects of thermally-induced pile head displacement on normal service.