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Thermoactive geostructures are considered an economically suitable and environment-friendly solution for heating and cooling buildings. Energy tunnels have gained growing interest in recent years because of the large ground volume involved in heat exchange in comparison to building foundations. Heat exchange is obtained by embedding a circuit of pipes into the precast concrete lining, resulting in a reduction of the initial costs of installation with respect to standard low-enthalpy geothermal solutions. In this paper, thermal activation of the twin tunnels of the II line of Warsaw metro, Poland, is considered with the aim of evaluating the geothermal potential of the line. Thermohydraulic finite-element analyses were performed on a number of representative cross-sections, considering site-specific hydrogeological conditions based on the Engineering Geological Database of the Capital City of Warsaw. Results demonstrate that the thermal activation of the two 1·6 km-long tunnels could exchange up to 5·3 and 5·8 GWh in the heating and cooling seasons, respectively. Furthermore, the influence of the local geological conditions on the exchangeable heat rate was investigated. The results form a basis for a preliminary assessment of the shallow geothermal energy utilisation potential for the design of further extensions of the metro line in Warsaw.

Intensive development of railway infrastructure in Poland is associated with significant support provided for that purpose by the European Union, especially, by investments in the modernization of existing railway lines. Together with the improvement of the infrastructure in less developed countries, an interoperability of rail system at the international level is sought through the technical harmonization, mostly by the introduction of European regulations and technical standards. The paper presents the main requirements associated with the geotechnical aspects of design of railway embankments, mostly relating to their overall stability and maintenance of serviceability. Some aspects of the European standards as well as international, national, and internal regulations, are discusses in the context of challenges encountered by designers. The main geotechnical issues are associated with safety requirements, loading conditions, geometry of railway embankments, as well as the scope of geotechnical investigation necessary to make an informed decision on a final design solution.

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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.