Synthesis of a benchmark exercise for geotechnical analysis of a thermoactive pile

Thermoactive piles ensure a dual function: they support mechanically the superstructure and at the same time they are used as heat exchanger elements. In comparison to standard design practice, this requires considering the associated thermal loadings from the operation of the heat exchange system. To assess the thermal effects on the mechanical behaviour, different design assumptions and modelling approaches can be used. Therefore, within the framework of European Cooperation in Science and Technology Action TU1405 ‘Geothermal Applications for Buildings and Infrastructures’, benchmarking of a single geothermal pile has been performed. Hence, both heating and cooling of the pile were considered while different rigidities (representing the upper structure) on the pile head were assumed. The results show that a broad range of design assumptions could be used, which unfortunately lead to noticeable differences. Although the main focus was on the methods and assumptions employed, the exercise also opens questions about the influence of transient effects, thermal strains in the ground, temperature cycles and so on. Owing to the complexity of the topic, some of them were just mentioned, while others were addressed in greater detail. In general, the findings emphasise the need for further practice-oriented guidance to be presented in design guidelines and standards.