A Unified Soil–Structure Interaction Method for Load–Settlement Design of Energy Piles

Energy piles are a dual-purpose geostructure system designed to serve both as load-bearing foundations and as a means of utilizing geothermal energy for heating and cooling buildings. Due to their dual function, the behavior of energy piles under temperature variation at the pile-soil interface is significantly more complex than that of traditional piles. This study introduces a simplified analytical method for predicting the load-settlement curve of energy piles by incorporating the effects of softening skin friction, hardening end-bearing resistance, and soil-pile interaction. The uniqueness of the proposed method lies in its ability to predict the load-settlement response of energy piles under specified pile head loads or settlement conditions by solving a cubic equation while also being able to separate end-bearing and skin-friction resistances - a capability not available in existing approaches. The proposed model was validated against a well-documented case study, including reported interface shear testing and full-scale field tests for energy piles. The comparison results demonstrate a close agreement between the proposed approach and the behavior observed in the field. The findings demonstrate that the proposed method improves upon existing approaches for designing energy piles and offers a valuable tool for determining the thermal-mechanical behavior of energy piles, particularly in softening scenarios.