New construction of the Albula Tunnel in the Swiss Alps
Even 110 years after the 1st tube through the mountain, the challenges for the engineers are still great
This time the engineers were warned that they would be faced with difficult rock from 1127.5 m of driving: we are talking about the new construction of the Albula Tunnel in the Swiss Alps, where extreme problems had arisen during the first tunnel construction 110 years ago just at 1192 m, that the work was completely suspended for 9 months and that in the end only with unprecedented efforts was the railway line through the mountain completed.
This time the problem zone with 21 m length was completely icy. This is the current technique when working in such a rock.
We learn: a mountain is not at all a mass of hard material, but can also be a kind of “paste”, for example, as it says on the website of the project: at 1192 m (after tunnel entrance Preda) we are dealing with a skeleton of rock with mud fillings, and on top of that there are heaps of crevices in this zone, from which ice-cold water shoots out at a pressure of 6 atmospheres. On the webpage, the inner life of the mountain is described as “floating” at this point.
At Preda, on the other hand, everything starts almost comfortably. Allgäu slate is first of all the material that is easily degradable and stable.
But more and more water-bearing fissures appear until the problem zone with Raibler-Rauwacke follows. In the 1st tunnel, the walls in this area did not even manage to stabilize at first – in 2.5 months, only 6.3 m progressed. Only with “the heaviest support measures” was it possible to get back into solid material.
Then follows a largely problem-free stretch of 55 m with mylonite, which is repeated later with 66 m length.
From there to the end in Spinas, one has to deal with Albulagranite. Under this name different rocks like granites, granodiorites and gabbros are summarized. Even if there are smaller fault zones, the mountain is unproblematic for the miners here – so much so that in the first tunnel they even refrained from cladding the walls in places.
Pedro Traquina - Area Sales Manager