Performance-based design of energy piles in the framework of Eurocodes

Employing geostructures as structural supports and geomaterials as reservoirs for the extraction and storage of heat represent effective means to meet human activity needs since ancient times. This master thesis focuses on the thermo-mechanical behaviour and performance of an innovative, multifunctional technology that couples the roles for the structural support and energy supply of any type of built environment, i.e., energy piles. The multifunctional role of energy piles involves mechanical and thermal loads applied to such geostructures. These loads pose unprecedented challenges to engineers because they cause variations in the temperature, stress, deformation and displacement in the subsurface that need to be considered during analysis, design and verifications. Prior to this work, a substantial amount of design procedure had been made available to address the mechanical performance of single energy piles or of group energy piles. However, energy pile foundations are subjected to thermal load that made born a new stress and displacement fields into the structures. In this framework (i) limited applications, if available, to quantify the thermo-mechanical behaviour and performance of energy single pile subjected to thermal and mechanical loads; (ii) no simplified procedure were accessible to perform the design of energy pile groups against the action of such loads; (iii) no comprehensive framework for the reliability of the analytical models for general situations (e.g. layered soil); (iv) no simplified procedure that take into account the long-term action for several years of thermal load. To address such challenges, this master thesis was performed to (i) provide a complete and simplified procedure to perform the design of the energy piles group in according with Eurocodes Standards at ULS (e.g., geotechnical and structural) and SLS; (ii) provide an important guideline about the reliability of the analytical models in a real design situation; (iii) provide clarity about the effects of the long-term effects (e.g. stress and displacement fields) during the design situations. The results presented in this thesis suggest the conclusion that (a) the thermal effects change the stress and displacement fields within the pile; (b) in average the best analytical model is layer model and (c) long-term actions have an important role during the stress and displacement verifications.