In the immediate vicinity of the sounding tunnel under Brienz slide, both the water pressure in the rock and the sliding speed have decreased. This gives hope that deep drainage and thus remediation of the landslide can work. However, further research is still needed.
Since September of last year, an exploratory tunnel has been built in solid rock under Brienz Slip. It should provide information as to whether “deep drainage” of the landslide is possible. The excavation of the tunnel has now been completed. Four holes from the surface and two from the tunnel are now used to measure how the water pressure has changed since the tunnel was built. At the same time, the change in the rate of landslide in the various parts of the landslide is monitored. The measurements show that the water pressure has dropped significantly in some cases.
The sliding speed near the tunnel has also declined. “We are very satisfied with the way things have gone so far,” says the responsible geologist Daniel Figi from the BTG Office of Technical Geology. Water is the decisive driver of landslides: “You can imagine it like a water slide. If it is dry, you only slide moderately fast. But as soon as water flows, you slide much faster,” summarized Mayor Daniel Albertin at Thursday's municipal meeting. “The same effect also occurs in Brienz slip. If we can drain the water from him, the landslide can slow down. Although the findings do not yet allow us to assess whether a tunnel with holes can actually calm the landslide as desired, we are confident.”
Whether the tunnel is working will be known in spring 2023
In the next few weeks, further holes will be drilled from the tunnel into the solid rock. By the end of October, it will be evaluated how the pressure conditions in the rock and the slide rate will change as a result. “We must take this time to observe the course of water pressure changes in detail and draw the right conclusions,” says geologist Daniel Figi. “The rock under the landslide is very firm and almost impermeable to water. As a result, changes in water pressure occur only slowly.”
It is therefore not until November that the ground is drilled from the bottom down to the slippery mass and then measured again how water pressure and slide velocity change. “This allows us to differentiate which of our measures has which effects on water pressure and slide velocity,” says Daniel Figi.
In spring 2023, based on the evaluations of measurements in and around the exploratory tunnel, a decision will be made as to whether the probe tunnel will be converted into a drainage tunnel. More about that 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.