„Wir nehmen dem Gebirge damit den Druck weg.“ We are taking the pressure off the mountain. That is how Sepp Kurath, project manager of the drainage tunnel under Brienz/Brinzauls in the Albula valley, described the work to SRF in May 2026. The physics is a century old. Karl Terzaghi’s principle of effective stress says fractured rock holds together through grain-to-grain friction, while water pressure in the pores pushes the grains apart. Lower the water pressure and the same slope grips harder. Graubünden bet CHF 39.8 million on testing that idea at the scale of a village.

This is an older story, re-read with hindsight. The decisions date from 17 August 2023 and 12 November 2024. The hindsight figures run from February to July 2026, and the latest slide reading is from May 2026.

The 2023 bet

On 17 August 2023 the Graubünden government approved a drainage tunnel of over 2 km, extending the existing exploration gallery beneath the slide. Eligible costs were CHF 39.8 million, 90 % of it carried by the Confederation and the canton. The target was precise: the “Dorf” slide below 10 cm a year. The canton’s release also stated that effectiveness and reach were uncertain, and that there was no comparable alternative. A public client named a number, named its doubt and built anyway. That honesty is the part worth copying.

The 2024 test

The mountain did not wait for the tunnel. According to the canton, the village was moving just under 250 cm a year in autumn 2024. A precautionary evacuation followed on 12 November 2024, and tunnelling continued “at full speed” to protect the homes, the RhB Albula line, the Albula and Julier roads and the power lines. The 92 residents stayed out for 62 weeks, until the evacuation was lifted from 26 January 2026.

The 2026 reading

SRF reported on 6 February 2026 that the slide had slowed to 10–25 cm a year in December, the lowest in 15 years, with only a quarter of the boreholes drilled. Geologist Reto Thöny said that, in the team’s assessment, evacuations in the next few years were “wenig wahrscheinlich bis unwahrscheinlich” (unlikely to very unlikely). By 14 April the municipality counted 20 lateral and 13 upward boreholes draining about 1,100 l/min, with water in the monitoring boreholes falling about 6 m a month.

On 12 May the news agency sda reported a slide rate below 5 cm a year, with some survey points unmoved since March, and 49 residents back home. Geologist Daniel Figi said the data show good chances of reducing the slide significantly over the long term. The tunnel was then almost 80 % built. Each blast round means 56 drill holes, about 120 kg of explosive and just over 3 m of advance. The miners who repeat that cycle are the people this result rests on, and almost nobody knows their names.

←TODAY: As of May 2026, a partly built tunnel had cut the slide by a factor of about fifty, from roughly 250 cm to under 5 cm a year.
→3012: Zurich-3012 treats groundwater the way we treat columns today, as a drawn and maintained load path.
Fulcrum: Water is a load, and a slope is designed like a foundation.

What stays open

The village remains in the red zone. Mayor Daniel Albertin says 5 to 10 more years of observation are needed before that could change, and RhB trains still pass at 30 km/h. Kurath again: „Es bleibt eine Aufgabe für kommende Generationen“ (it remains a task for coming generations). Albula/Alvra approved CHF 82.56 million gross on 10 July 2026, by 41 votes to 3, for the households that choose to leave. 42 applications remain. Ten objections, mainly about flat-rate compensation, are with the canton. Staying and leaving are both reasonable answers to the same mountain. The trade-off is plain: drainage buys time only as long as someone keeps the boreholes clean and the data flowing. As PAZ argued about the Mattertal line, a protected asset is a running cost, not a finished object (our MGBahn piece).

Atelier: Most Swiss site plans show contours and boundaries but not the water moving underground. As Alpine permafrost and rainfall patterns shift, the hydrogeologist’s report belongs in the first design meeting, not in an annex. Monday move: add a “groundwater” layer to your Archicad or Rhino site template, showing flow direction, drainage outfalls and the body responsible for them.

Hack: Turn a drop in water level into the pressure it removes from the soil. Each metre of head lowered cuts pore pressure by about 9.81 kPa, and that relief is extra grip for the slope. Run it in GhPython or plain Python:

gamma_w = 9.81  # kN/m3, unit weight of water
for dh in (1, 6, 12):  # metres of head lowered
    du = gamma_w * dh  # kPa removed from the pores
    print(dh, "m ->", round(du), "kPa more effective stress")

The 6 m row is Brienz’s monthly figure from April 2026. Before your next site plan leaves the office, find out where the groundwater goes and who drains it.