Thermo-mechanical performance of energy pile groups

Thermal active piles have demonstrated to be among the most suitable and effective application of energy geostructures. This research was aimed at providing insights on the thermomechanical performance of such foundations. It was shown that soil and structure mechanical properties have a similar impact on the overall response of the foundation when subjected to vertical loads and uniform temperature variations. This suggests that a unique design strategy can be applied to achieve good performance.

The local performance of single energy piles was investigated with respect to potential effects of concrete cracking. Numerical analyses showed that the structure is able to accommodate the imposed strains simply by providing a minimum ductility capacity. The latter corresponds to the minimum reinforcement ratio for conventional reinforced concrete ties.

The question of potential induced geotechnical failure was also examined, and attention was drawn on the fact that imposed displacement loads, such as the temperature variation, cannot cause a collapse by loss of equilibrium due to the intrinsic ductile behavior of a pile embedded into the soil. However, induced plastic strains at the soil-pile interface might cause undesirable settlements under serviceability working conditions. It may be concluded then that stability criteria can be met by simple conceptual design, whereas settlements criteria require some additional analyses.

It is hoped that such outcomes can help to achieve an optimized, cost-effective and more resilient design of thermo-active foundations, which have a great potential to shift the built environment under the light of the sustainable development.

Project information: Swiss National Science Foundation N°174575, COST Action TU1405.