Evaluation of Head Restraint Effects on Energy Foundations

Abstract

This paper presents an evaluation of the impact of head restraint on the thermomechanical response of centrifuge-scale energy foundations. Specifically, the head movement and axial strain response of an end-bearing energy foundation installed in a dry sand layer was evaluated during thermal response tests with both load-control and stiffness-control head restraint conditions. During the thermal response test, an axial load is applied to the head of the foundation in either load or stiffness control after spin-up of the centrifuge, then heated fluid with a controlled temperature is circulated through heat-exchanger tubing embedded in the foundation. In both tests, the foundation was heated from a temperature of 23 to 33°C was then maintained until foundation head displacements and axial strains had stabilized. The test performed under stiffness-control conditions was found to expand by a slightly lower amount and had lower axial strains and higher axial stresses near the ground surface. The axial strain distributions lower in the two foundations were similar.