17.10.2017 - First breakthrough in the Albula Tunnel
A further milestone has been reached in the construction of the Rhaetian Railway's (RhB) new Albula Tunnel with the breakthrough into the cavern. On Tuesday, 17 October 2017, the miners taking care of the headwork from Preda broke through the last pieces of rock face which were separating them from the cavern. That means the trickiest zone of the mountain range has been conquered. Since the start of the headwork at the end of August 2015, over half of the total 5,860 metres of the planned tunnel has been cleared. The main breakthrough of the Albula Tunnel is expected to take place in late autumn 2018.
It happened just before lunch: the miners doing the headwork from the Preda side handed the statue of the patron saint of tunnel builders, Saint Barbara, over to their comrades from the headwork team from Spinas. The breakthrough into the cavern was the conclusion of the trickiest part of the headwork for the new tunnel: overcoming the geological fault zone 'Raibler Rauwacke'. On the occasion of the breakthrough RhB Director Renato Fasciati praised the efforts of everyone involved in the project, thanking them for their great commitment and wished them every success for the remaining period of construction.
Geological difficulties well mastered
So far the Albula massif has presented planners and workers of the new tunnel with quite a few hard nuts to crack. Alongside the highly acquiferous Allgäu slate, a great challenge was particularly how to master the fault zone 'Raibler Rauwacke' at tunnel metre 1,300. To be able to build a tunnel through this unstable layer, it was iced up over several months in an elaborate process. The cavern was created for this purpose. For around nine months the 'Rauwacke' was frozen to -15 degrees from here over a length of 60 metres and with a diameter of around 17 metres. In the protection of this ice casing, the 20-metre fault zone was able to be overcome. After that, the tunnel walls were stabilised with a 1.2-metre ring of concrete containing a multi-layer, water-pressure-resisting vault seal. At the end, the freezing devices were dismantled and removed. With the breakthrough from the Preda side, the cavern is now being integrated into the new tunnel. The main breakthrough of the Albula Tunnel is expected to take place in late autumn 2018.