The construction procedure

What's on the horizon in 2020?

In 2020: the final spurt for the new U5! The structural work has been completed in all underground stations, as has the track construction. The station finishing works are now in full swing everywhere. The conductor rail is to be put into operation as early as the end of April.

The Final Touches to the Stations

The stations Unter den Linden and Rotes Rathaus are being completed. At both stations, the final stages of the interior are being carried out, from the station lighting to the wall panels and the rear track walls. At the same time, ticket vending machines, ticket validators and information showcases will be installed. At the Museumsinsel Underground Station , which will open in the summer of 2021, the areas relevant to operations must also be completed by the start of trial operations in June. Therefore, BVG's own tradesmen, from the cable maintenance department to the electricians, are busy installing the electrical systems along the entire route.

Starting in June: Trial Operations

Trial operations will begin in June, initially testing the interaction of the individual components and units in continuous operation. After that, all drivers on the new line will have to get to know it personally and drive it. So there is still a lot to do. If corona doesn't throw a spanner in the works, passengers will be able to ride the new U5 from Hönow to the main station at the end of the year. A concrete date for the ceremonial opening will be announced in time.

© A. Reetz-Graudenz
The Construction Process

Official ground-breaking ceremony

The construction project was 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 then serving mayor of Berlin Klaus Wowereit, the then 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.

Afterwards, 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.

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, telephones 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 – Berlin's Water Authority, Vattenfall Utilities and Deutsche Telekom – had to reroute their lines. This is a complex process that demanded careful planning and coordination, because most of the lines were 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, an explosive ordnance removal team searched and scoured the building ground for bombs, ammunition and similar dangerous objects.

When the construction site was set up for the tunnel boring machine's (abbr. TBM) starting shaft at Marx-Engels Forum, the Marx–Engels Monument located there had to be shifted a few meters to the side to also make way for the track-switching system and logistics center.

Underground Civil Engineering for the Excavation Pits

Since Berlin’s level of groundwater is relatively high, water was expected to be just two to three meters below the surface of the ‘U5 gap closure’-site. This made 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 were excavated, wood panels were installed on the sides and on the bottom of the pit to ensure that it stayed 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

After the excavation pits had been made, the TBM drove the tunnels.

The tunnel tubes for the U5 gap closure were constructed using the shield driving method. The tunnel boring machine "Bärlinde" travelled underground from the Marx-Engels-Forum to the Brandenburg Gate underground station and built the tunnel carcass at the same time. In the area of the future underground stations Museumsinsel and Unter den Linden, it passed through the unguided excavation pits.

After completion of the tunnel drive, the tracks were laid in the tunnels. The tunnels are currently being equipped with the necessary technology.



© A. Reetz-Graudenz

Successful structural work

After "Bärlinde" had completed its work, the shell construction began at the underground station Unter den Linden. Within the excavation pits, the soil was excavated and the tunnel tubes in the U5 platform area were demolished. Then elements such as walls, intermediate ceilings, stairs and platform could be concreted. In the Rotes Rathaus underground station, this also included the complex concreting of the mushroom head columns. In 2016 the structural shell of the Rotes Rathaus underground station was completed, followed a year later by the Unter den Linden underground station. Since then, the extension has been underway at both underground stations.

Due to its special location, the underground station Museumsinsel represented a special case in the structural work. Since the station is located directly under the Spree canal, the central section, which later forms the platform, could not be built using the open method. Instead, the entire platform area had to be constructed using the mining tunnelling method. This was done under the protection of a 28,000 cubic metre frost body - the largest inner-city glaciation in Europe to date. The shell was completed at the beginning of 2020, and since then the expansion has been running at full speed here too.

Track works

After completion of the structural work in the underground stations Rotes Rathaus and Unter den Linden, track construction began. First the track trough was concreted and the special mass-spring system was installed, which reduces the noise pollution of the underground trains to a minimum. Then wooden sleepers and rails were laid and the ballast was laid and distributed. With the completion of track construction in the subway station Museum Island at the beginning of 2020, the line from Hönow to the main station will be complete. Now the necessary technology is being installed - from signalling systems to the conductor rail, which will be switched on at the end of April.

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