Effects of Head Restraints on Radial Thermal Responses of an Energy Pile Embedded in Cohesive Soil

This study presents field tests on an energy pile embedded in cohesive soil and subjected to building loads. The effects of head restraints on the radial thermal responses of the pile were comparatively analyzed. The results reveal that the beam foundation provided poor insulation between the atmosphere and the near-surface soil layer. The radial thermal influence radii at the mid-depth of the energy pile ranged from $3.5D$ to $1.5D$ ($D$ is the pile diameter) when operating from 24 h to 8 h daily. When additional mechanical loads were applied to the pile heads, the axial thermal strains decreased, and the radial thermal strains increased; the ratios of axial thermal strain to radial thermal strain decreased by 83% for piles embedded in clay/silty clay and by 18% for piles embedded in dense sand; the responses of radial and axial thermal stresses increased by 33% and 11%, respectively, for piles in clay/silty clay and by 11% and 48%, respectively, for piles in dense sand.