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Construction phase 4
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