Long-term Performance of Energy Piles Subjected to Cyclic Thermal Loading in Sand

In order to improve the design of the energy pile, the long-term performance of a freehead energy pile in dry sand was analyzed by using a sequentially coupled thermal-stress analysis approach. In the analysis, the bounding surface model was used to describe the mechanical behavior of sands under cyclic loadings. The effects of the seasonally cyclic thermal loading on the pile displacement, the shaft friction, and the factor of safety were studied in detail. It was found the temperature cycles leaded to the accumulation of the settlement at the pile head, and the accumulated settlement increased with the static working load level and the temperature cycle number. The location of the null point controlled the relative displacement pattern between the pile and the soil, which affected the distribution and the development of the shaft friction. Due to the volumetric contraction of sands, the negative friction was induced at the upper part of the pile,and the shaft friction at the lower part of the pile was reduc