Numerical study of the response of a group of energy piles under different combinations of thermo-mechanical loads

Energy piles are rapidly gaining acceptance around the world because they represent a renewable and clean source of energy that can be used for the heating and cooling of buildings, and the de-icing of infrastructures. This technology couples the structural role of pile foundations with an energy supply using the principle of shallow geothermal energy. The exploitation of geothermal energy represents an additional thermal load that is imposed to the foundation and the surrounding soil. Because the primary role of energy piles is the stability of the overlying structure, this aspect must be ensured even in the presence of the additional thermal load. This study summarises the results of 3-D thermo-hydro-mechanical finite element analyses that investigated the behaviour of a group of energy piles for which field data were available. This allowed the nearly unique validation of the numerical approach with experimental data and a confirmation of the reliability of the results. The work provides a summary of the foundation behaviour under both conventional and extreme thermal loading conditions with reference to a geothermal operation of the piles for cooling and/or thermal energy storage applications within one season. The interaction between the piles is studied and the thermally induced group effects analysed. Attention is dedicated to the vertical stress and displacement developments in the piles. The results presented in this study outline crucial aspects that may be considered by engineers for the geotechnical and structural designs of such geostructures.