Thermal activation of tunnel infrastructures: insights from three Italian case studies

Half of the energy consumption of the European Union is comprised by heating and cooling, which are largely dependent on energy fossil fuels. In contrast, renewable energies only represent 18% of the heating and cooling production. This Thesis focuses on the integration of energy geostructures, namely tunnels, as renewable sources for heating and cooling applications. The research explores the concept of energy tunnels which are characterized by both thermal and structural behaviors and the harnessing of the ground temperature. In particular, the study addresses the thermal activation of tunnel linings, where heat exchanger pipes are embedded to capture geothermal energy in an efficient way. The present Thesis provides an insight INto the current state of the art, which involves several projects around the world such as the Turin Metro Line 1 and 2, the Lainzer tunnel in Vienna, the Stuttgart-Fasenhoff Tunnel, amongst others. The Thesis focuses on the study of three different projects in Italy such as the Subport Tunnel in Genova, the Trento ring road tunnel and the Cortina d'Ampezzo tunnel. For each project, a brief description of the works is provided as well as their geotechnical, geothermal and hydrogeological frameworks. Based on the geothermal characterization of each site, homogeneous sections with similar geothermal properties along the chainage of the tunnels are identified with the purpose of estimating the total geothermal potential along the chainage. For this purpose, nomograms derived from the literature that provide the geothermal potential with respect to the ground temperature and the groundwater velocity are consulted. Finally, the work includes the creation of a 3D finite element model for the case study of the Subport Tunnel of Genova. The model is created to have a better understanding of the role of the seawater temperature in the evaluation of the geothermal potential. Following a sensitivity analysis, the outputs of the numerical model are thoroughly discussed and motivated.