Main challenges for the New Mont Cenis base tunnel

Year 2025 will mark a turning point in the construction of the Mont Cenis base tunnel with the start of systematic tunnel boring machine (TBM) excavation, after awarding and start of the main works on the French and Italian sides in recent years. This step follows more than 20 years of studies and reconnaissance work, which have led to the creation of an exceptional project, which, once completed, will be the longest twin‐tube railway tunnel in the world. The article first traces the study and reconnaissance phase, trying to show the complexity and considerable effort that was necessary to go forward with the current ongoing project. In particular, very significant means of study and reconnaissance were necessary to allow the start of the works in acceptable and controlled technical conditions. Then, the article presents the design choices that were made to address the technical challenges and requirements related to the expected functionality. In addition to the technical aspects and the vast range of complex situations that can be encountered, the main works were started following specific contractual models, aimed at a more equitable sharing of risks, in particular considering the impact of implementation times on the cost of the work. In conclusion, the main technical, environmental, and implementation challenges that characterize the project will be highlighted, making it unique and innovative. At the end of December 2024, the excavation progress for all works is 25 %.