I’ve written about a few different railway stations located under mountains, but this is something new – one located under a river!
The station is Zürich Selnau on the Zürich S-Bahn system in Switzerland, and has an underground platform located beneath the River Sihl.
With the station entrance emerging from the middle of the water.
The original Bahnhof Selnau was the above-ground terminal station for the Sihltalbahn, made up of the Uetliberg line which opened in 1875, and the Sihltal line which opened in 1892.
However the terminus lacked a direct connection to the city’s main station of Zürich Hauptbahnhof, and the private railway operator could not afford to acquire a surface route or build an underground connection, and so the two railways were left disconnected.
The construction of a U-Bahn system in Zurich was seen as a way to fix this, but after the project was voted down in 1973, the Zurich City Planning Office began studying options to extend the Sihltalbahn to form part of an expanded S-Bahn system.
And in 1983 a decision was finally made – an underground extension along the River Stil, reusing an unused underground platform already built at Zürich Hauptbahnhof for the rejected U-Bahn scheme.
Swiss Engineer and Architect No. 18 describing the selected route:
The extension of the SZU
The long-awaited connection Selnau-Hauptbahnhof
By R. Theo Balz
Overview of the new line:
The new route begins on the western side edge of the former and now disused Zurich-Selnau train station. In a covered steep ramp the route reaches a 5% incline to the level of the new Selnau station under the Sihl bed between the Stauffacher and Sihl bridges.
The double track railway line continues underneath the Sihlbett on the right edge of the river to the Gessner Bridge and leads then over a tight curve in two single-lane tubes under the pedestrian level of Zurich Hauptbahnhof. The new route is a total of 1592 meters.
The Selnau underground station replaced the previous Selnau terminus. The central platform is accessible from the Stauffacher and Sihl bridges.
Concerns about drainage:
Sihl floods as well as the urban planning aspects had to guide this solution.
Based on model tests on the Research Institute for Hydraulic Engineering, Hydrology and Glaciology from ETH Zurich, it could be proven that a staircase 5.35 m wide through the drainage profile of the Sihl directly onto the Sihlbrücke is possible without significantly hindering the flood flow.
Work started in March 1986, and by 1987 work on the new underground railway was well underway.
Sheet pile walls separated the excavation pit from the rest of the river during construction. To reduce the cost of construction, it was decided that these walls would not be unnecessarily high, but that the construction site would be allowed to floor if the river rose – a scenario which happened once during the project, without causing any major damage.
Other innovate design features included the use of ballastless track laid on on spring-loaded concrete slabs to minimise noise and vibration transmission to nearby buildings; and low-maintenance solid conductor bars for the supply of overhead power to trains.
On 4 May 1990 original terminus at Selnau was closed, when the new rail extension and station under the River Stil was opened, which now form lines S4 and S10 of the Zürich S-Bahn.
Today the site of the original terminus at Selnau is a housing estate, with the original station building built in 1892 having been demolished.
Footnote: a literal ‘underground’ music festival
By the autumn of 1988 the concrete shell of the new Selnau station had been completed, and so it was used as the venue for a two day folk festival.
Temporary stairs proving access to the platform.
Where a beer hall had been set up.
- Sihltal railway line at Wikipedia
- Zürich Selnau railway station at Wikipedia
- Swiss Engineer and Architect No. 18, May 2, 1991 (German-language)
- Sihltal Zürich Uetliberg Bahn – Under the Sihl to the Centre (German-language)