BLS AlpTransit AG, client for Switzerland’s 34.6km long Lötschberg tunnel has accepted responsibility for extensive settlement damage to the Alpine village of St German situated above the tunnel’s southerly portal at Raron. The settlement reached a maximum 183mm and has affected some 40 buildings, mostly in the form of cosmetic cracks, although four of these buildings will require more detailed attention.
Peter Teuscher, director of BLS AlpTransit, said, “Of corse we accept responsibility for the damage caused. We want to proceed in a non-bureaucratic fashion and are currently in dialog with those affected to repair any damage.”
An expert team from the University of Lausanne has compiled a preliminary report on the situation that claims the settlement, including troublesome differential settlement, was caused when the excavated tunnel became a natural drain for the water table directly above the alignment. The settlement and building damage was due to desiccation and shrinkage of the underlying sediments following the groundwater drainage and was not connected to vibrations from the drill and blast method of tunnel advance. The village lies over a 60m deep fault plane, at depths of 12m and between 46-59m, were ground conditions considered at an early stage to be potential settlement hot spots.
The readings began to stabilise at the beginning of March and have now almost stopped. The research team has emphasised this saying, “no noticeable movements are anticipated in the long-term future.”
Currently a general planner from the Architect Office Bürcher & Albrecht will propose how best to repair the damage, coordinate the repair work and appoint the necessary contractors for the repairs, scheduled for completion by the end of this year.
The tunnel contractor JV MaTrans consisting of Marti/Waltergruppe/ Porr/Balfour Beatty is continuing work on the 5.3km drive north from Raron and reports that the situation has not affected production and that tunnelling is progressing.
The JV is constructing two sections of the tunnel, the Raron section and the 3.1km long Steg spur tunnel, with a combined worth of $315M.
The full Lötschberg tunnel when in operation in 2007 will link Frutigen in Kandertal with Raron in Wallis and is currently 49% excavated. As part of the $14bn AlpTransit scheme the tunnel is vital for Switzerland’s bid to transfer all heavy freight through the country from road to rail.
Related Files
Figure 1: Diagram of the affected water table and St German village and their position relative to the tunnel
