Frankfurt a. M.

Extension of the U5 Europaviertel metro line

tunnelling, specialist civil engineering and structural engineering – all from a single source

Extension of the U5 to the Europaviertel

The Europaviertel lies to the west of Frankfurt city centre on the site of the former main freight station. In recent years, residential, office and commercial buildings, as well as public open spaces, have been developed along Europa-Allee. The extension of the U5 will create a new section of line between the existing light rail network and the Europaviertel. From Platz der Republik, the line initially runs underground to Güterplatz station. It then reaches the surface via tunnel sections constructed using the cut-and-cover method and a ramp structure. Even before the platforms, access points and track layout became visible, the tunnel tubes and construction pits for the new section were created deep beneath Frankfurt’s streets.

With EVA beneath the Europaviertel

For the enclosed tunnel section, two parallel tunnel tubes were constructed using shield tunnelling. The southern tube is 827 m long, whilst the northern tube is 842 m long. The EVA tunnel boring machine, weighing around 580 t and measuring approximately 80 m in length, was used. Its name stands for ‘Connecting the Europaviertel’. The machine was adapted to the geological conditions along the route. Excavation of the southern tunnel tube took place between September 2019 and September 2020. EVA was then retrofitted for the second phase of excavation. From January to May 2021, the tunnel boring machine constructed the parallel northern tunnel tube. A total of 8,358 tunnel segments were installed during the excavation. The prefabricated concrete segments, assembled in a ring-shaped configuration, form the inner lining of both tunnel tubes.

The final metres to the existing tunnel

The connection to the existing underground tunnel at Platz der Republik was carried out using conventional mining methods by July 2022. Around 11 metres of tunnel were excavated in the southern tube, with a further 3 metres in the northern tube. Due to the groundwater conditions, the work was carried out under pressurised air conditions. Pressurised air locks equalised the air pressure between the work area and the surrounding environment. Workers accessed the respective work areas and returned via pressure chambers. The work was carried out in shifts, each lasting six hours. A further one and a half hours were required for entering and exiting the pressure chambers. The personnel involved underwent occupational health examinations in accordance with the project-specific requirements. Metre by metre, the connection between the new tunnel tubes and the existing U5 line was thus created.

Ramp structure along Europa-Allee

In parallel with the mechanised tunnel boring, the tunnel sections along Europa-Allee were constructed using the open-cut method, as well as the adjoining ramp structure. The light rail is guided from the underground section to the surface via the approximately 306-metre-long ramp. The floor, walls and ceiling elements were constructed in sections and connected to the tunnel structures that had already been built. The ramp structure thus forms the transition between the tunnel beneath the Europaviertel and the above-ground light rail route along Europa-Allee.

Construction pit for the Güterplatz station

The construction pit for the new Güterplatz underground station was created in the heart of Frankfurt. It is approximately 170 metres long, up to 30 metres wide and reaches a depth of up to 24 metres. To create the construction pit, approximately 170,000 tonnes of soil were excavated and removed. The excavation was carried out in sections and was coordinated with the work on the excavation enclosure, the bracing levels as well as the existing tunnel tubes. In the area of the future station, the tunnel segments previously installed by the tunnel boring machine were dismantled section by section. Once the final depth had been reached, the concrete base as well as the station floor were constructed.

Since 2024, the station’s reinforced concrete structures have been under construction within the construction pit.

Building between the city centre, the tunnel and the new route

The works took place in the vicinity of existing roads, buildings and technical infrastructure. Tunnel driving, station construction, the construction pit, the ramp structure and the connection to existing infrastructure all had to be coordinated within the overall project schedule. PORR’s structural engineering, tunnelling and special civil engineering divisions were involved in various sections of the light rail extension. The project scope encompassed services ranging from mechanical and mining-based tunnel excavation, through construction pits and structural work, to the construction of the above-ground connection. Step by step, the structural link to the Europaviertel was thus established between the existing underground network and the new route.

Basis for the extended U5

Where freight trains once reached Frankfurt’s main freight station, the extended U5 light rail line will run in future. Beneath Europa-Allee, two tunnel tubes connect the existing line with Güterplatz station and the adjoining ramp structure. The construction of the tunnel tubes, the connection to the existing line, the station excavation pit and the open-cut tunnel sections formed the key structural elements for the new light rail link. The construction of the structures along the new section was characterised by the use of the EVA tunnel boring machine, segmental lining, pneumatic tunnelling and reinforced concrete construction. Step by step, the structural foundations for the extension of the U5 between the existing light rail network and the Europaviertel were thus laid.

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