3. Full Scale Geothermal Energy Pile Studies at Monash University, Melbourne, Australia

Geothermal energy piles are dual-purpose structural elements that provide structural support to built structures and act as heat exchange units to supply space heating and/or cooling. This chapter presents results from two studies conducted on full scale geothermal energy piles installed at Monash University, Melbourne, Australia. Study 1 focused on the thermal and thermo-mechanical behavior of a single pile, installed in December 2010. It showed that the pile and the ground required at least more than twice the heating time to return to initial thermal conditions. Furthermore, it has been found that the pile shaft capacity increased after the pile was heated and returned to the initial capacity (i.e., initial conditions) when the pile was allowed to cool naturally. This indicated that no losses in pile shaft capacity were observed after heating and cooling cycles. A variance in average vertical thermal strains was observed at the end of the heating periods. These were almost fully recovered at the end of the cooling periods indicating that they were of an elastic nature. Study 2 involved a group of energy piles (two piles) installed in October 2014 as part of the pile foundations system of a multi-story residential building. They will become operational at end of year 2015 when the superstructure is completed. Initial observations related to concrete curing indicate that concrete was initially in tension due to the cement hydration process but reversed to compressive strains once it cooled down and its temperature was in equilibrium with the surrounding soil.