Construction

The U55 Shuttle Line from Hauptbahnhof to the Brandenburg Gate

Underground construction of the final cross-section of the station takes place in several stages. This is the longest building phase. All work is done underground, in order to keep disturbances to a minimum.

Inbound and outbound traffic at the site is the only obvious sign of the subterranean work in progress.

The first phase consists of drilling micro-tunnels around the future cross-section that extend the entire length of the site. Piping for a cryogenic system is then installed in these micro-tunnels. A cryogenic unit then freezes the water in the soil via these pipes. This creates a thick coating of ice and sand which keeps out the groundwater.

Protected by these frozen conditions, the tunnel "breakthrough" is made from the initial shaft east of Wilhelmstraße. The soil that remains is reinforced immediately thereafter with gunned concrete. After each segment is completed, the actual load-bearing reinforced concrete cross-section is then installed into this "gunned concrete" tunnel.

Work proceeds segment by segment until the station reaches its final length.

Construction phase 4: Digging the ducts

Action:
Cryogenic drilling of water-bearing sandy soil; two-stage tunnelling excavation of the station under protective frozen conditions

Emissions:
Little or no noise pollution because construction operations are underground. Moderate noise pollution from loading and traffic.

Material transport:
Removal of excavated earth, delivery of concrete and gunned concrete (on-site silo)

Site traffic:
approx. 2-3 lorries per hour