U 55 Berlin

Right in the middle of Berlin, in direct vicinity of the Brandenburger Tor and surrounded by influential embassies as well as the famous Adlon hotel, the subway station Brandenburger Tor is built under the protection of the ground freezing technique. Until the subway line is continued to Alexanderplatz, Brandenburger Tor station will be the terminal station of the U 55 line – starting from the main station via the Reichstag up to the Brandenburger Tor. The building project will be realized using a driving of the main tunnel as well as two side tunnel drivings running in parallel. In order to insert the freeze pipes, 30 microtunnels with a diameter of 1,600 mm and a length of 90 metres were arranged around the excavated cross section. Due to filling the microtunnels using grout the freeze pipes are heat conductive and integrated in the ground in a statically effective way. For the freezing operation, a total of four cascade refrigeration plants with an installed total cooling capacity of 1,200 kW will be used.
The cooling circuit with about 90 m³ of brine is operated at a flow rate of up to 300 m³/h. The brine temperatures are -38 °C in the feed of the freeze pipes. As an innovative building optimisation, eight microtunnels located in the excavated cross section of the side tubes were filled with water. During the maintenance and tunneling phase of the centre tube, this water is integrated into the static system as ice. Before driving the side tunnels these microtunnels are unfrozen using a heat circuit, and the steel tubes of the microtunnel are retreated.
That way, difficulties during the retreating work of the microtunnels in the cross-section are avoided as well as involved vibrations during the excavation. The scope of services of this freezing project include:
  • installation and removal of the brine feed tubes, the freezing units and the brine circulation pumps
  • installation and removal as well as control of systems for measurement, approx. 800 temperature sensors are installed
  • control of the freezing system during the freezing up phase and in the intermittent maintenance phase as well as adjustment of the freezing system to the different excavation and building phases
  • planning, control and monitoring of the innovative method "water-filled microtunnel"



Frankfurter Ring 105
D-80807 Munich, Germany
Phone + 49 89 350607-11327
Fax + 49 89 350607-25
This email address is being protected from spambots. You need JavaScript enabled to view it.