Thermo-mechanical behaviour of energy pile considering non-uniform initial ground temperatures

Ground temperature varies along the vertical direction at shallow depths, and its influences on the thermo-mechanical response of energy piles during heating and cooling processes remain unclear so far. The aim of this paper is to fill this gap by performing finite-element numerical analysis based on Comsol Multiphysics software, taking energy piles in the Yellow River flooded area as an example. A three-dimensional numerical model is established and is then validated by comparison with published experimental results. Parametric analyses are conducted with a focus on the heat exchange efficiency, temperature distribution, displacement and axial stress of energy piles caused by heating in summer and cooling in winter. It is found that the ignorance of ground temperature variation could lead to: (a) overestimation of the heat exchange efficiency in both winter and summer; (b) underestimation of pile head displacement in summer and overestimation in winter; (c) overestimation of the axial stress in summer and underestimation in winter.