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Closing the gap in the U5 and fitting out the station at Rotes Rathaus

Facts and Figures
Company PORR GmbH & Co. KGaA
Principal BVG represented by PRG U5
Location Berlin - Germany
Type Rail and road tunnels
Runtime 04.2016 - 12.2019

A monumental project comes to fruition

The 2.2km long U5 gap closure section extends the U5 line from Alexanderplatz to Brandenburg Gate and links it up to the U55 line. In the course of closing this gap, two new tunnel tubes were constructed west of the Rotes Rathaus city hall over a distance of 1.6km using the shield tunnelling method. PORR Civil Engineering was responsible for the eastbound section. It was in charge of the general refurbishment of the four-track Alex tunnel, including the construction of the track system, as well as the structural work and extension of the Rotes Rathaus underground railway station.

Service ports allow large equipment and material to be transported to and from the site
Built in 1930, the 350m long Alex tunnel terminated as a cul-de-sac. It served as a parking and turnaround facility for metro trains until May 2016. The structure is around 15m wide and between 4.7m and 8.9m high. The upper edge runs approximately 3.5m below street level on average. This means that the tunnel is almost completely embedded in groundwater. Two covered, crane operated 10.6m x 4.6m logistics ports were installed for the complex site logistics. This allowed the large-scale equipment and materials to be delivered without being affected by metro operations.

Adding ballast to prevent the tunnel from floating
Gutting the tunnel reduces its weight and disrupts the statics of the system. The tunnel structure had to be prevented from floating by all means, because this would weaken the cross-sections and increase the risk of cracks and water entering the tunnel. The team added ballast to the tunnel sections and used pressure-controlled presses when installing new and additional columns. The refurbishment was carried out in 1.5m wide sections using the pilgrim step method and was monitored by surveyors.

Fitting out the Rotes Rathaus underground station
The fit-out of the Rotes Rathaus station took place slightly later. Designed by Collignon Architecture and Design, the new station features striking mushroom columns and walls clad in light and dark terrazzo panels. Glazed intermediate levels provide transparency. The fit-out comprised both the public and non-public areas of the station on levels -1 to -3. In addition to the classic trades such as glazing, carpentry, metalwork, plastering and tiling, the technical facilities for the lifts, indoor ventilation, building automation, sanitary facilities, fire-fighting and underground train operations were also constructed under the direction of the Civil Engineering division.