No abstract

Energy pile foundation technology has received increasing attention as a means for reducing energy requirements for space heating and cooling and cutting down the emission of carbon dioxide. Energy piles provide a means for efficiently transferring heat to and from the soil underlying a structure, providing a heat source for heating and a heat sink for cooling of spaces within the structure. Currently the design of energy foundations relies heavily on empirical methods, owing to a limited understanding of coupled cyclic thermo-mechanical effects on pile behavior, particularly long-term performance in clay. Moreover, there is lack of field data since it is expensive and time-consuming to carry out field trials. Based on theoretical derivation, geotechnical centrifuge modelling permits the simulation of heat diffusion phenomena at a rate N 2 times (where N is scaling factor) than in prototype. It is thus beneficial to assess long-term behaviour of energy piles by the use of centrifuge modelling technology. In this study, a new heating and cooling system developed for centrifuge modelling at the Hong Kong University of Science and Technology (HKUST) is described. The heating and cooling system is comprised of an array of thermoelectric coolers and an electrical-resistance heating coil. Ethylene glycol is used as a heat exchanger fluid to transfer the thermal energy from the heating and cooling system to tubular aluminum model piles via insulated piping with the help of a pneumatic pump. The heating and cooling system is able to control the temperature of the pile over the range from 3°C to 90°C. To assess the long-term serviceability of energy piles in stiff clay, a centrifuge model test was carried out where five cycles of heating and cooling were applied to a single energy pile under a sustained working load at 40g. Test results revealed that a ratcheting settlement pattern was induced after cyclic thermal operation.