Abstract: Energy piles are piles equipped with heat exchange pipes through which a heat-carrying fluid circulates and exchanges heat with the ground. This technology couples the structural role of classical pile foundations with heat exchangers for energy supply. In order to analyze the bearing characteristics of energy piles in clay, it is necessary to determine the temperature response of the pile and the ground, so as to investigate the effects of temperature on mechanical behavior of the soil. With the use of the finite element software ABAQUS, a numerical approach has been developed to evaluate the thermal response. In this method, the heat transfer process is simplified as the thermal convection between the fluid and the pipe wall, the thermal conduction in the pile, and thermal conduction in the ground. Validation of the proposed method is carried out by comparing the computed results with the theoretical solutions and data from literature. A thermo-bounding surface model is implemented into ABAQUS. The ability of the model to describe the temperature effects on mechanical behavior of clays is verified by several examples. Based on the numerical heat transfer method and the implemented constitutive model, the long-term performance of a free-head energy pile in normally consolidated clay is analyzed. In the analysis, three different load levels are considered. The effects of the seasonally cyclic thermal loading on pile settlement, shaft friction, and axial force are studied in detail.

Key words: energy pile, clay, cyclic thermal loading, thermo-plasticity, mechanical behavior