If the sounding tunnel is successful under Brienz slide, it should be extended and expanded into a drainage tunnel. Experts from cantonal offices, engineering and geology have studied three possible variants. Two of them are being followed up.
For experts from the Department of Forest and Natural Hazards and the Civil Engineering Department, an extension of the now built exploratory tunnel towards the village and the mountain is the most promising variant of a drainage tunnel. This “Route 1” leads from the current end of the tunnel west of the village to the border between landslide village and landslide mountain. Two tunnel arms, each 500 meters long, are to be built here. The entire tunnel is built in solid rock under the sliding mass.
“With the extension to a drainage tunnel, the building will be three times as long as it is today. The tunnel and additional drainage holes should ensure that the landslide is significantly slowed down,” explains Josef Kurath from the Grisons Civil Engineering Department. “The village of Brienz/Brinzauls should be inhabited in the long term and the traffic routes and lines should be protected from further damage caused by landslides.”
A second tunnel is also being tested
In terms of mining, tunnel construction in solid rock has so far been problem-free and the drainage through the tunnel and the additional holes appear to be working. For this reason, the extension of the probing tunnel to the drainage tunnel should also be carried out completely in solid rock under the sliding mass (variant 1).
In addition, a second lug within the sliding mass should also be tested (variant 3). “Such a tunnel would encounter completely different conditions during construction. The sliding mass is likely to be very jagged, completely different from the solid rock in which we have built so far. Construction would be more difficult, slower and therefore more expensive,” says engineer Josef Kurath from the Grisons Civil Engineering Department. Over the next few months, particularly experienced tunnel construction experts will be examining whether such a construction is even technically feasible.
Another variant was rejected: It would have intended to extend the exploratory tunnel straight under the village and down to under the “Igl Rutsch” landslide (variant 2). “This project is unlikely to be feasible,” explains Josef Kurath. “The tunnel would leave the solid rock and push through the approximately 20-meter thick, loamy sliding layer into the slippery mass. In terms of mining technology, this would be a very complicated and potentially dangerous project.”
“Our hopes are initially based on extending the exploratory tunnel in solid rock,” states Mayor Daniel Albertin. “I am impressed by the performance of the teams who have built a tunnel in such a short time that gives the impression that it could slow down the Brienz slide.” Project planning work for this extension will begin in mid-August. The planning documents for the project edition and the submission for the search for potential entrepreneurs are created.
The project planning costs 1.4 million francs. If everything goes without objections, construction of the drainage tunnel could start in October 2023.
More about the Previous findings from the exploratory tunnel here.
More information about Brienz Rutsch at www.brienzer-rutsch.ch.
This article was published in the 32nd Brienz Rutsch bulletin of the municipality of Albula/Alvra. Christian Gartmann has been the information officer of the municipality of Albula/Alvra for Brienz Rutsch and a member of the municipal management staff since 2019.