Underground infrastructures and the importance of the people’s safety and structures robustness are relevant and contemporary issues in the civil engineering industry. The demand for this infrastructural typology has developed to such an extent that the need for a better and cost-beneficial knowledge of the risks is necessary. This thesis aims at bridging and developing further the knowledge on Fire safety engineering and structural engineering on the particular topic of spalling failure. Another objective of this thesis is the discussion over the possible replacement of the used procedures used to assess and guarantee tunnel safety. Both from a fire safety and structural engineering point of view, prescriptive measures and solutions are mostly proposed to accomplish a safe tunnel design. This causes the design to be non optimised and in some cases more costly than what is actually needed. From the fire safety side, the use of pre-given fire curves is put under discussion. Research has been conducted to asses which are the origins of the most widely used curves. Studies have also been performed to develop a practical analytical engineering method to analyse and estimate the consequences of a given fire scenario tailored to the specific tunnel under consideration. Subsequently the results of the analytical models have been compared with the results obtained with advanced Computational Fluid Dynamics tools. Finally, more complicated scenarios have been studied with the use of this software. On the other hand, from a structural engineering point of view, a new model able to describe the spalling mechanism has been proposed. The model predicts the spalling time for NSC elements and at the same time verifies which is the optimal thickness for the piece to spall. On top of that the possibilities for further use of the model in the description of the spalling mechanism for HSC and PPFRC elements have been investigated. Finally this two topics have been combined together and conclusion have been drawn.