Traversing the Piora Basin

14 October 2008
Fearful stone
Fearful stone

The notorious dolomite-anhydrite mixture of the Piora Basin proves a headache for the engineers. Its sugar-grain consistency seems likely to prevent tunnelling. But this obstacle too is overcome. (1997, Keystone)

Traversing of the Piora Basin is completed on 15 October 2008 in the east bore - a milestone for the Gotthard Base Tunnel. The basin had been much talked about, not just among geologists and engineers but also the general public and parliament. The sugar-grain dolomite, which was subject to high water pressure, threatened to endanger construction of the entire tunnel. During the planning phase, the Piora Basin had been investigated by means of an exploratory bore comprising a 5.5-kilometre tunnel.

« The water pressure measured in the tunnel equates to the difference between the hydraulic potential and the topographical height of the tunnel. »

Federal Institute of Technology Zurich, Geothermic investigations of the Piora Basin, p. 15, 01.06.1997

Menschen Technik Wissenschaft: Mehraufwand auf der NEAT-Baustelle im Tavetscher wegen weichem Kakirit-Gestein

2001, ©1970-2005 Swiss Radio and Television, licensed by Telepool PLC Zürich

Menschen Technik Wissenschaft: Mehraufwand auf der NEAT-Baustelle im Tavetscher wegen weichem Kakirit-Gestein

Menschen Technik Wissenschaft: Soft kakirite rock making the job harder at the NRLA construction site in Tavetscher, 2001 (©1970-2005 Swiss Radio and Television, licensed by Telepool PLC Zürich)

250 metres

height above the tunnel where the feared zone of sugar-grain dolomite ends; the rock in the tunnel-boring zone proves to be hard.

19 exploratory bores

in total drilled to analyse the Piora Basin between 1993 and 1998

10 metres

average distance covered by the tunnel-boring machine per day in this area

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