Thermal-mechanical behavior of deeply buried pipe energy pile group in sand obtained from model test

Abstract

One practical and effective method for shallow geothermal development is energy piling. This research presents the deeply buried pipe energy pile (DBP-EP), which has a wide range of potential applications and can collect deeper geothermal heat from the pile toe. This work conducts a model test investigation of the thermal–mechanical behavior of the DBP-EP group in sandy soil because the construction of the former differs from that of the common inside buried pipe energy piles (IBP-EP). The findings indicate that the heat exchanger tube at the pile toe of DBP-EP will be extended outward for heat exchange with the soil, in contrast to IBP-EP, and that the temperature change at the pile toe is greater than that of the whole. The pile cross-section strain decreases gradually from inside to outside along the radial direction. The axial earth pressure change rule around the pile is larger at both ends and small in the middle. For every 1℃ that the inlet temperature raises, the pile top’s final displacement increases by roughly 0.11‰$D$. At various inlet temperatures, the DBP-EP group heat transfer rate per meter drops by 8% − 23% when compared to the single pile’s. The average axial earth pressure difference surrounding the pile gradually rises when the pile top is not loaded, while the pile side friction difference of the pile group reduces in comparison to that of the single pile. The variations in pile side friction, axial earth pressure surrounding the pile, and pile top displacement of the pile group are reduced when the pile top is loaded because of the dense effect between the pile and the soil. This study contributes to the theoretical understanding of the design and practical implementation of DBP-EP structures.