LININGS | TECHNICAL
The ‘Wurm’ lining and installation system used for the southern lots of the Gotthard Base Tunnel PHOTO CREDIT: HERRENKNECHT
mode TBM with a diameter of 10.02m is to excavate the tunnel on the Italian side using segmental lining. The excavated material generated by the project
will be reused across national borders. For the first time in Europe, the circular economy principle is being applied here on a binational jobsite. Another six railway base tunnels are under
construction or already completed to facilitate crossing the Alps with similarly flat routes: in Switzerland and Austria, these are the Gotthard (57km), Brenner (64km in total), Koralm (32km), Semmering (27km), Ceneri (15.4km), and Lötschberg (34.6km) tunnels.
1.1 Geological parameters The Mont Cenis Base Tunnel will cross the outer Alps on the French side and the inner Alps on the Italian side and is located in one of the most complex geological systems in Europe. Here, very diverse rock types such as granular soils (alluvial deposits), gneiss, granites and rock formations (schist) are encountered, requiring different excavation methods depending on the geological sector being traversed. In order to get an accurate picture of the geological system of Mont Cenis, approximately 65km of drill cores were extracted and analysed, leading to the identification of seven geological areas and the decision as to which sections should be put out to tender for either mechanised or conventional tunnelling.
2 - GRIPPER TBMS FOR LOT CO5 The two identical Gripper TBMs with Wurm are being used by the joint venture of Eiffage, Spie batignolles, Ghella and Cogeis in section CO5 of the Mont Cenis Base Tunnel, which crosses the border between Italy and France underground. The construction lot
begins at the Villarodin-Bourget/Modane access tunnel, crosses the Ambin massif and reaches the underground safety zone of Clarea. In addition to the 18km of tunnel excavated by each
of the two Gripper TBMs, two 7.8km-long tunnels are being built using conventional methods. Then there is all the associated logistical work and the underground safety zone in Modane. The overburden at the deepest point is over 2,200m. The TBMs, specifically developed for the
requirements of the CO5 jobsite, have numerous special features designed both for initial tunnel support and for overcoming any geological difficulties. For excavation, the TBM braces itself directly against the previously excavated tunnel wall with its two lateral gripper shoes. Four cylinders press the rotating cutterhead onto the tunnel face, which breaks up the rock ahead with its 62 disc cutters. The excavated material is taken from the tunnel face via the muck ring to a belt conveyor, which transports the material out of the tunnel. Depending on the rock class, the excavated tunnel
can be temporarily supported with shotcrete or steel arches. In addition, both exploratory drilling and rock anchoring can be carried out to secure the rock mass. Even by Herrenknecht’s standards, at 334m in
length, the Gripper TBM is very long. This is due to two bridges integrated into the back-up. The bridges will be used to help concrete 30m of invert every day, on which the Wurm will later also run. The Gripper TBMs will drive two base tunnel tubes
from France toward Italy. Five teams of 25 people will operate each machine in three shifts, 24/7. Once each Gripper TBM, including the back-up, has
completed the first 2km-3km two of tunnelling then the pre-installed Wurm can begin its work.
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