Baulos 1 W-5, U-Bahnhof Gern mit Strecken

The entire construction lot is located in the upper quaternary groundwater table in thick beds of gravel with a groundwater level of up to 13 m above the base of the tunnel. In some places, the bases of the tunnels and the station building intersect the tertiary marl. As the upper groundwater table cannot be lowered, the station is being completed in a thick trough comprising bored piles. The shield drive is accomplished with a hydro shield with fluid-supported face. The bentonite suspension mixed with soil is pumped off via a pipe system, cleansed from the soil it contains via a coarse sieve and a two-stage hydro cyclone unit and subsequently returned to the face via pipes. The means by which the shield tunnelling machine travels out and in to the starting shaft and the station or target shaft are worth to mention. In this connection, following the setting up of the excavation around the station and the shafts, so called sealing cells in the form of an overcut wall of bored piles made of a cement-bentonite mass were created and pumped dry. Injections were carried out on the excavation wall in the drive-in zone as well as in the target zone. The shield machine first of all moves into the empty sealing cell under atmospheric conditions in the zone consolidated by injecting. Subsequently, the supporting fluid can be filled in the shield and the sealing cell is flooded, after a light connection has been created between the segmented tube and the support wall of the starting shaft or station. Then the shield machine passes through the piles of the sealing cell. When driving in, the shield machine first of all moves into the flooded sealing cell. As soon as a watertight connection has been created through shield tail pressure grouting between the segmented tube and the piles, the sealing cell is pumped dry and the supporting fluid discharged. The shield machine can then be moved into the station or target shaft through the opening cut in the excavation wall.

Country: Germany
Region: Bayern
Tunnel utilization: Traffic
Type of utilization: Underground, urban and rapid transit
Client: Landeshauptstadt München, U-Bahn-Referat
Main construction method: Trenchless
Type of excavation: Shield machine (SM)
Lining: Reinforced concrete segments
No. of tubes: 2
Tunnel total length: A total of 1,425 m including a 210 m station built by cut -and-cover and 2 single-track tunnel tubes altogether approx. 1,175 m in length driven by shield as well as starting and target shafts
Cross-section: approx. 42 m²
Contract Volume: 129.3 mill. DM
Opening: June 1996