Different types of energy piles with heating-cooling cycles

Energy piles are a new kind of foundation that can exchange heat with the surrounding soil. The long term thermal mechanical behavior of energy piles is important to the safety of the structure. Because different heat exchange piles may be used in practice, a comparative analysis under the same heat input is needed. This model test was conducted to assess the effects of cyclic heating and cooling on the thermo-mechanical behavior of semi-floating energy piles. Three types of energy piles with heat exchangers in U-shaped, spiral, W-shaped configurations were subjected to three heating and cooling cycles and a constant working mechanical load in dry sand. Results showed the pile temperature, horizontal earth pressure and thermal strain after heating and cooling cycles nearly recovered to the initial levels. The thermal stress increased gradually after each heating-cooling cycle. With a working load equal to 50 percent of the ultimate capacity, the settlement of each pile accumulated at the end of each cycle. In the end, the settlement of a W-shaped heat exchanger pile was larger than other two piles reaching 0.56% of the pile diameter. The displacement produced in each heating and cooling cycle decreased as the cycle increased.