The axial and radial thermal responses of a cast-in-place energy pile, 10 m long and 0.6 m in diameter, installed in unsaturated sand under a six storey building are examined during a heating–cooling cycle. The instrumentation in the pile was configured to compare radial and axial thermal responses at the same elevations and to evaluate the temperature and axial thermal stress distribution across the cross-sectional area of the pile. The magnitudes of the axial thermal strains were more constrained than the radial thermal strains at all depths, leading to the development of axial and radial thermal stresses of up to –4.5 and –0.015 MPa, respectively, for a change in average pile temperature of 24.1 °C. The magnitudes of the radial thermal stresses with changes in pile temperature were significantly lower than the axial thermal stresses at all depths of the pile, indicating that the radial thermal expansion had negligible effects on the development of axial thermal strains and stresses. The temperature distribution over the cross section of the pile showed low variations at all depths, indicating that it would be justified to consider a uniform temperature distribution at least in piles of similar dimensions and with even heat exchanger layouts.

The thermal response of an energy field scale pile that is part of a pair of energy piles spaced at a centre-to-centre distance of 3.5 m (i.e., 6D, where D is the pile diameter), was examined experimentally and numerically. Three field tests were conducted to assess the axial and radial thermal responses of the energy pile: (i) heating of the energy pile alone, (ii) heating of both energy piles simultaneously, and (iii) heating of the other energy pile while the considered energy pile was not heated. Good agreement was obtained between the experimental and numerical evaluations of the energy pile during the tests. A parametric study of the validated numerical model was performed for each of the three tests to understand the effects of varying soil thermal conductivity, thermal expansion coefficient, and elastic modulus on the thermal response of the considered energy pile. The numerical results confirmed the field results that radial thermal stresses in the energy piles were insignificant compared to axial thermal stresses. The impact of elastic modulus of the soil was more significant on the thermal stresses of the energy pile compared to the effects of soil thermal conductivity and thermal expansion coefficient. The thermal stresses of the considered energy pile were not significantly affected when both energy piles were heated simultaneously, even though ground temperature changes between the energy piles were more significant due to thermal interaction. Only minor thermal effects on the non-thermal pile were observed during heating of one of the energy piles for different soil properties.