The largest of four contract packages on the Lötschberg Baseline Tunnel Project North section has been awarded to an international JV comprising Ilbau (Austria), the JV leader,/Walo Bertschinger (Switzerland)/ Dumez-GTM (France) and Skanska (Sweden). The six-year $347m Mitholz Basetunnel Lot 45.3 North contract was awarded in February 2000 and comprises a total of 25-26km of single-tube, single-track, drill+blast rail tunnel. Work on site started in February 2000 and tunnelling is expected to begin in July 2000.
Tunnel excavation will advance from the access tunnel at Mitholz, with one face going north towards the Frutigen portal and two faces going south. It is expected that each point of attack will complete some 8 000m of the 62m² single-tube tunnel. Drill+blast is the chosen method of construction, with support systems required for rock classes III-V. Rockbolts, wire mesh, shotcrete and steel arches will provide support elements in the hard rock formations of the Alps. Maximum overburden on the tunnel alignment is about 2000m.
A particular difficulty anticipated is the expected risk of water inflows as well as methane gas, which will be detected by means of advance probe drilling. The tunnel will be finished with an in-situ concrete lining.
There was an option in the tender documents for a TBM drive in the North tunnel advance, although the South running tunnels were specified to be performed in drill+blast due to the high overburden limiting the geological and geotechnical site investigations required for a successful TBM application.
Other sections of the Lötschberg Baseline Tunnel project will employ TBM technology but the Mitholz Basetunnel Lot 45.3 North contract JV priced the contract on a full drill+blast excavation. The client’s design engineer for the contract is Ingenieurgemeinschaft E+B/IUB.
The contract is scheduled to be completed and handed over by February 2006.
Related Files
Lötschberg Baseline Tunnel
