Mont-Cenis Base Tunnel: How the Lyon-Turin Rail Link Is Being Buried Under the Alps

The B1M visits a colossal engineering project beneath the Alps, where the Mont-Cenis Base Tunnel will form the core of a new Lyon-Turin railway. The video explains how base tunneling through a mountain base enables near-flat tracks for faster trains, details the drilling and blasting and tunnel boring machine (TBM) work, and highlights the project’s impact on travel times, freight volumes, and CO2 emissions. It also covers the challenges of geology, water ingress, cross-border coordination, funding, and local opposition, painting a vivid picture of one of Europe’s most ambitious infrastructure megaprojects.

Introduction and Project Scope

The Mont-Cenis Base Tunnel is the central element of a 270-kilometre rail corridor between Lyon and Turin, with 57.5 kilometres spent tunneling beneath the Alps. The goal is to halve journey times, reduce road freight, and create a more balanced multimodal transport network across Europe. The cross-border section is managed by Tunnel Europan Leon Turin (TET), with shared governance between France and Italy and substantial EU funding.

Tunneling Techniques and Key Innovations

The project uses a mix of drill and blast for fragile rock and TBMs for more stable segments. Seven TBMs will operate simultaneously, including the Viviana, a 10.4 metre diameter hard rock TBM built to dig a 9 kilometre stretch. The TBM carries a lining system of concrete segments, with a goal of manufacturing 100,000 segments to form stable tunnel rings. A conveyor system removes excavated material, much of which is reused on site for lining and embankments, illustrating the project’s emphasis on material efficiency.

Geology, Water, and Ground Support

Exploration tunnels revealed 80 geological domains, from alluvial deposits to ancient gneiss, each with distinct behaviour. Ground conditions required a combination of methods, including raise boring to access ventilation shafts and four vertical shafts extending from surface to the base tunnel. Water ingress is managed through pumping and treatment, turning a potential risk into a resource for dust suppression and drilling operations.

Timeline, Costs, and Public Response

The project faces a €25 billion price tag, with EU funding covering a significant portion. Delays and local protests have marked its development, but a joint France-Italy-EU timetable approved in 2025 aims to commission the base tunnel by 2033. Once complete, the railway is expected to support up to 22 long-distance passenger services daily and shift substantial freight from road to rail, contributing to decarbonisation goals.

Impact and Future Vision

Beyond France and Italy, the Mont-Cenis Base Tunnel fills a critical gap in the Mediterranean corridor of the Trans-European Transport Network, enabling easier east-west travel and accelerating continental growth while reducing emissions. The project embodies modern civil engineering through a combination of deep tunneling techniques, cross-border collaboration, and a strong emphasis on safety and sustainability.