Effect of nearby piles and soil properties on thermal behaviour of a field-scale energy pile

Abstract

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.