First cross-border TBM unveiled for Mont Cenis base tunnel

The 10.4m, 334m-long machine is the fourth of seven TBMs delivered to excavate the tunnels of the Lyon-Turin line, and the first for the twin tunnels that will cross the border.

The ELYOT group of companies, comprising Eiffage Génie civil, Spie batignolles génie civil, Ghella and Cogéis, will deploy the gripper TBM to excavate 18km of one of the two tubes of the Mont Cenis base tunnel, between the Villarodin/Bourget-Modane access adit in France and the Clarea underground safety site in Italy.

A gripper TBM was chosen because of the geology of relatively compact, uniform and stable formations; the depth of the tunnels, with more than 2,200m of overburden; and geotechnical considerations, such as detachments and convergence. There are also the high temperatures present at such depths, which were highlighted by the exploratory tunnel of La Maddalena in Chiomonte, which was used to establish the TBM’s specification.

While excavation is under way, shotcrete support will be applied to the walls, along with bolts and ribs. Behind the TBM, a 650m-long machine called the Würm (worm) will fix the final concrete lining.

CO5 construction site on the Mont Cenis base tunnel crosses the border between Italy and France. It starts from the Villarodin-Bourget-Modane access adit, passes through the Ambin massif, and reaches the underground safety site of Clarea.

At the same time as the 18km-long twin tunnels are excavated, 7.8km of tunnels will be dug using conventional methods. In addition to these works, all connected and logistical works will be carried out. In total, around 15km of tunnels will be built using the conventional method, including the underground safety area at Modane.

Maurizio Bufalini, general director of Tunnel Euralpin Lyon-Turin (TELT), said: “It is the fourth TBM that we have come here to receive in Schwanau and, as ever, it is always a great thrill. Its twin will be ready in February, and then it will be the turn of the two Italian TBMs. We will then have no fewer than seven of them digging to complete the 57.5km tunnel, the longest railway tunnel in the world.”

CO5 project director Salah Ghozyel said the job site was exceptional “in terms of size, logistics, simultaneous excavation using both conventional and mechanised methods, along with the technical and human resources mobilised, all of which are constrained by the single access point provided by the Villarodin-Bourget/Modane access adit”.

“All this means that the group of companies and all those involved will need to be truly adaptable,” he said.