By Lynda Myer
Herrenknecht’s 10.4m, 334m-long TBM, that is due to construct the tunnel across the French-Italian border for the new Lyon-Turin railway has been unveiled, while it is the fourth of seven TBMs delivered to dig the tunnels of the Lyon-Turin line, and the first for the twin tunnels that will cross the border.
In order to boring 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, responsibility of deploying the gripper TBM will be up to the ELYOT group of companies, comprising Eiffage Génie civil, Spie batignolles génie civil, Ghella and Cogéis.
Considering that the geology is almost compact, uniform and stable and the tunnels have over than 2,200m of overburden; and due to geotechnical considerations, such as detachments and convergence, a gripper TBM was chosen for this project. Additionally, 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.
The operation of lining tunnels with shotcrete will be done to the walls during that excavation is undergoing, along with bolts and ribs, whereas fixing the final concrete lining will be done behind the TBM by a 650m-long machine called the Würm (worm).
Passing the border between Italy and France, CO5 construction site on the Mont Cenis base tunnel commences from the Villarodin-Bourget-Modane access adit, crosses through the Ambin massif, and reaches the underground safety site of Clarea.
Through conventional methods digging process of 7.8km of tunnels will be implemented while the 18km-long twin tunnels are excavated. 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.
According to Maurizio Bufalini, general director of Tunnel Euralpin Lyon-Turin (TELT): “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.”
“The job site was exceptional in terms of size, logistics, simultaneous excavation using both conventional and mechanized methods, along with the technical and human resources mobilized, 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,” said CO5 project director Salah Ghozyel.
