Centrifuge modelling of energy piles subjected to heating and cooling cycles in clay

Energy pile foundation can expel and extract heat into and from the ground in summer and winter, respectively. The discharge and extraction of heat induce cyclic thermal load in piles and may lead to serviceability problems. So far, the effects of cyclic heating and cooling on the heave and settlement of energy pile have not been fully understood. In this letter, a new in-flight heating and cooling system developed to control cyclic temperatures of energy pile in centrifuge is described. This system is able to control cyclic temperatures in an energy pile between 3℃ and 90℃. By using this system, two centrifuge energy pile tests were carried out to investigate the effects of cyclic heating and cooling between 9℃ and 38℃ on the long-term displacement of single energy pile in slightly and heavily overconsolidated kaolin clay. Under a constant working load, distinctive ratcheting displacement mechanism was observed for both energy piles during five cycles of heating and cooling. The pile embedded in slightly overconsolidated clay (OCR=1.7) continued to settle but at a reduced rate and reached at 5.7%D (pile diameter). This is believed to be caused by thermally accelerated creep and irreversible contraction of slightly overconsolidated clay. In comparison, a settlement of 3.1%D was observed for pile constructed in heavily overconsolidated clay (OCR=4.7). The observed ratcheting settlements of piles have a clear implication on the serviceability design of energy piles.