The construction procedure

Official ground-breaking ceremony

The construction project is launched with an official event.

The ground-breaking ceremony for the U5 gap closure took place outside Berlin City Hall in April 2010 and was attended by the serving mayor of Berlin Klaus Wowereit, the Senator for Urban Development Ingeborg Junge-Reyer and the then Chairman of the BVG Management Board Andreas Sturmowski.

Site clearance

Due to considerable construction and rerouting work in Berlin prior to the beginning of our project, the building site had to be cleared before the actual work could properly begin.

Then archaeologists from the Berlin Monument Authority undertook a search for historical relics that may have survived below the soil and ultimately rescued many objects especially outside the city hall that were left to posterity,

Below the ground of the construction site were also a large number of pipes and cables for electricity, drinking water, sewage, gas and district heating, telephony and cable TV as well as connection lines for traffic and street lights. In order to safeguard all cables and lines from the construction works the organizations responsible, including Berlin’s water authority, utility Vattenfall and Deutsche Telekom, had to reroute their lines. This is a complex process that demanded careful planning and coordination, because most of the lines are installed above one another, they generally had to carry out their works in succession.

To ensure that there were no unexpected interruptions from Berlin’s turbulent past, explosive ordnance searched and scoured the building ground for bombs, ammunition and similar dangerous objects.

As the construction site was set up for the tunnel boring machine’s (short TBM) starting shaft, the future track-switching system and logistics at the Marx-Engels-Forum, the monument of Marx and Engels which is located there had to be shifted a few meters to the side.

Underground civil engineering for the excavation pits

Since Berlin’s level of groundwater is relatively high, water is expected to be just two to three meters below the surface of the ‘U5 gap closure’-site. This makes it impossible for excavation to be 15 to 20 meters deep.

Therefore it is necessary to construct a waterproof – so when the different layers of sand are being excavated, wood panels are being installed on the sides and on the bottom of the pit to ensure that it stays waterproof throughout construction and after. This is mandatory to provide protection against groundwater and pressure conditions below the ground, such as earth pressure, water current or simply tensions.

Except for one small pit to construct an exit for the underground station Museums Island, all the excavation pits for the U5 gap closure have been completed.

Boring the tunnel

Once excavation works have been completed, they are being driven through by the tunnel boring machine to connect the stations to one another.

The so called ‘shield tunneling’ method is used to create the main tunnels for the U5 gap closure: the tunnel boring machine proceeds underground from the Marx-Engels-Forum to the connecting underground Brandenburg Gate station – building the tunnels structural work as works its way through. At the future underground station Museum Island and Unter den Linden, it passes through the excavations in which the groundwater level has not been lowered yet. This means that the pressure from the soil and groundwater is the same, inside and outside the pit, increasing stability during boring process.

Tunneling works on the northern tunnel have been completed, while the works to complete the southern tunnel began in April 2015.

Once the mechanical tunnel boring is finished, the connection to the underground station Brandenburg Gate will be built manually.

 

Preliminary station works

As soon as the tunnel has been completed, the foundations for the stations Museum Island and Unter den Linden can be excavated and the structural work can be constructed. Because of the fact that the tunnel boring machine does not pass through the underground station Red City Hall, the construction process there is not affected by the tunneling process itself. That’s one of the reasons why construction works here are the most advanced and workers are currently fitting out the modern stop right by the Berlin city hall.

The main tunnels are only required between the stations and are terminated in the station’s excavations.

Preliminary construction works are currently well underway at all three stations. The soil will gradually be excavated in the pits and the walls and floors of the station structures, intermediate ceilings, supports, track beds, platforms and else will then be built.

Finishing

The fit out process can start as soon as the structural work of the respective underground station is completed. This then includes pouring in gravel, track laying, installation of all cables, technical equipment for operations and the interior design.

Testing and commissioning

Once fit out works have been completed, the new infrastructure is extensively tested. In this phase of the project, the interaction of individual components and units is subjected to endurance testing.

After the testing phase has ended and the technical release has been granted by the respective authorities, the new section of the U5 can be officially commissioned.

The U5 gap closure project will then be completed and the new U5 will run from Hönow to Berlin Hauptbahnhof via the new undergorund stations Rotes Rathaus, Museumsinsel and Unter den Linden.

The U55 will no longer exist as such, due to the incorporation as part of the U5 extension.