The 2.3km long Chienberg tunnel on the Sissach bypass in Switzerland partially collapsed during construction in February.
A contracting JV of Batigroup, Frutiger and Itin was mid-way along the 10.2m diameter tunnel when Triassic marls and anhydrite fell in over a section of approximately 40m. Over a thousand cubic metres of ground is reported to have entered the bored tunnel.
A crater formed on the surface of Chienberg Hill, some 30m above the tunnel alignment measuring 25m across and 6m deep. No one was injured as the collapse occurred in open countryside and no properties are at risk.
Construction of the $US100M tunnel, began in January 2000. It was due for completion by the end of next year but the failure is likely to delay this by a few months.
A spokesman put the collapse down to "a totally unexpected geological event."
