Investigations on thermomechanical behavior of energy piles considering bearing stratum effects at pile end

As a new type of energy-saving technology, the energy piles have received increasing attention due to their dual functions of load bearing and heat transferring. The application of thermal loads poses new challenges for the design and serviceability performance of the energy piles. However, in the existing theoretical studies, the stress-deformation characteristics of the energy piles subjected to the combined thermomechanical loading under different bearing conditions have not been fully revealed. In this study, an analytical model for the energy piles under different bearing conditions is established based on the framework of the elastic analysis theory, taking into account the effects of the end-bearing layer. The model is validated against the field test data. This study focuses on analyzing the effects of geotechnical conditions and geometrical parameters of the piles on the load transfer and displacement behavior of the energy piles. The results show that the thermally induced axial loads increase with the stiffness of the bearing layer. Compared to the floating-bearing piles, temperature variations will cause greater thermal stress in the piles bearing on stiff soil strata. The stiffnesses of the end-bearing layer, surrounding soil and pile head are the critical factors affecting the magnitude and distribution of the thermally induced stress and displacement. The normalized calculated results obtained from the analytical model can be used to estimate the thermally induced stress and displacement of the energy piles in practice and provide a reference for the design and calculation of the energy piles under different bearing conditions.