Cross-sectional thermo-mechanical responses of energy piles

Despite the widespread research on energy piles, there remain critical knowledge gaps in the cross-sectional thermal responses of concrete energy piles. This paper implements a unique research approach by developing and validating a numerical model with cross-sectional temperatures and strains measured in a field-scale energy pile (diameter = 0.6 m and length = 10 m), strengthening the reliability of modelling for energy piles. The numerical model was used to investigate the influences of inlet fluid temperature, soil thermal conductivity, soil elastic modulus, soil thermal expansion coefficient, and the presence of a nearby energy pile at a centre-to-centre distance of 3.5 m on the cross-sectional thermal responses of an energy pile. These investigations demonstrate the practical significance of the above parameters on the cross-sectional thermal responses of energy piles. The results show that the temperature and thermal stresses were largest at the centre of the pile and reduced with increasing radial distance to the pile's edge, with differences up to 4 degrees C and 2.2 MPa, respectively, between the centre and the edge. A comparison of the cross-sectional results with existing stress estimation methods in the cross-section of the piles, commonly based on average cross-sectional temperature and temperature measured at a single spot, reveals that existing methods lead to an overdesign of 2 MPa. Therefore, the actual temperature and stress variations in the planar cross-section of energy piles should be accounted for in the design of energy piles.