Effects of soil thermo-plasticity on energy piles

Energy geostructures are spreading rapidly in Europe and all around the world. They represent a renewable and clean source of energy which can be used for heating and cooling of buildings, infrastructures and all kind of environment. This technology couples the structural role of geostructures with the energy supply, using the principle of shallow geothermal energy. Practically, a certain number of pipes are embedded into the concrete structure with a heat carrying fluid which circulates through them and exchanges heat with the ground. In particular, heat is extracted from the ground during winter, to satisfy the heating needs, and injected into the ground during summer, to satisfy the cooling needs. This represents an additional thermal loading, seasonally cyclic, which is imposed to the soil and the structure itself. This work aimes to investigate numerically the long term effects induced by the cyclic thermal loading on the soil around a group of energy piles and on the consequent displacements of the foundation. For this purpose, a finite element numerical model which reproduces an energy pile foundation is presented. The piles are subjected to a seasonally cyclic thermal loading, imposed in terms of injected-extracted thermal power, over several years.