LININGS | TECHNICAL
3 - THE WURM – A MOVING FACTORY The 650m-long installation and lining system behind the Gripper TBM, the Wurm, was used for the first and so far only time over 20 years ago during construction of the Gotthard Base Tunnel. As at the Gotthard, the Wurm for the Mont Cenis Base Tunnel is also a completely separate system that operates independently of the TBM. The use of the Wurm allows the interior lining to
be installed while the TBM is still advancing. The Wurm is designed as a large, moving factory: in the front section, the supply lines, ventilation duct and tunnel belt are initially detached for the Gripper advance; the tunnel is reprofiled if necessary; the formwork for the inner shell is placed in block lengths; and, the inner shell is concreted - before the supply lines, ventilation duct and belt are reattached. Development of the Wurm for the project is carried
out at Herrenknecht in close consultation with the specialists from the contracting joint venture. One of the biggest challenges here was to route the belt conveyor through the installation in such a way as to minimise conflicts with all other work. The design had to ensure that safety of the 20-25 workers on the Wurm was not compromised by the moving belt transporting the muck. At the same time, the performance of the belt conveyor must not be reduced over the entire length of the tunnel, i.e., around 18km. The optimal solution was to find three different
cross-sections with a defined position of the belt conveyor and the respective position changes in the Wurm: at the entrance to the Wurm; in the Wurm; and, at the end. The cross-sectional area of the Wurm where the inner shell is concreted, for example, is filled to the last square centimetre.
3.1 Work steps in the Wurm The concreting of the inner shell determines the speed of the Wurm, which is why it must be able to work and advance completely independently up to 2km behind the TBM. This means that the speed of the Wurm depends solely on how quickly all work is carried out, including sealing, formwork, concrete pouring, formwork removal, etc. There are two large formwork sections in the Wurm, each 10m in length. It has its own completely independent speed, which is determined by the geology as well as the speed of concreting.
3.2 Stations in the Wurm The space available in the Wurm is very limited, with an outer diameter of 10.43m and a later inner diameter of 9.40m. Fixed dimensions include the belt conveyor suspended from the tunnel ceiling, which is at least 1.50m-wide and up to approximately 2.50m high. Also on the ceiling is the ventilation duct, which has a diameter of approximately 2.40m. In the bottom section of the tunnel is the more
than 5m-wide concrete invert, on which the Gripper TBM and the Wurm advance. Here, a passageway
Schematic overview of operation of the Wurm lining and installation system for Lot CO5 of the Mont Cenis Base Tunnel PHOTO CREDIT: HERRENKNECHT
approximately 2.50m-high and 4.30m-wide must be provided for rail-bound jobsite traffic travelling in both directions, above which the Wurm is located. This lower passageway and the outer shell of the tunnel define the space available for all work that must be carried out in the Wurm during the individual phases.
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