Thermal design of quadratic segmental precast concrete driven energy piles

• Thermal analysis and design of segmental driven energy piles. • Effects of ground surface boundary conditions on the long-term performance of energy piles. • Use of G-functions for the thermal design of long quadratic driven energy piles. • Semi-empirical G-functions are faster and less computationally expensive. • Thermal performance of driven energy piles for two case studies in Norway. This paper introduces a novel thermal design methodology for segmental quadratic precast concrete energy piles. While thermal analysis methods for energy piles have been extensively studied, no previous research has specifically focused on long segmental quadratic concrete driven energy piles. Additionally, previous studies have applied fixed temperature boundary condition at the pile/ground top surface, which is the incorrect representation of the interface between the pile/ground surface and the building at the top. The main contributions of the present study are the development of semi-empirical G-function design charts, using a heat flux boundary at the pile/ground surface, and covering a wider range of energy pile lengths and soil and concrete material properties. A 3D finite element model was validated with thermal response tests on quadratic energy piles, and later employed to produce G-functions, applicable to longer segmental quadratic piles. The G-function design charts simplify the thermal design for practicing engineers and require minimum computational effort for long-term analysis. The results reveal that the pile/ground surface boundary conditions can affect long-term thermal performance by approximately 20%, though their influence is negligible in short-term analyses. The developed G-functions were employed to investigate two case studies in terms of ground temperature prediction for a quadratic driven energy pile under apartment blocks located in Oslo and Røros, respectively. The case studies showed that quadratic driven energy piles can cover 60%, and 48% of the heating demand for well insulated buildings in Oslo and Røros, during the design life of the buildings without adversely affecting the ground temperature.