Combined Solution Karlsruhe

Sub-project light rail tunnel with southern branch Ettlinger Straße

The ‘Karlsruhe combined solution’ comprises the two sub-projects ‘Kaiserstraße light rail tunnel with Ettlinger Straße south branch’ and the conversion of the ‘Kriegsstraße road tunnel with an additional tram line in a west-east alignment’. The Kaiserstraße light rail tunnel runs from Mühlburger Tor to Durlacher Allee and the southern branch runs from Marktplatz to Augartenstraße. The total length of the routes is approx. 4.6 km. The two tunnel sections include seven new underground stops and are connected by a triangle of tracks at Marktplatz. Construction was carried out without disrupting traffic and was optimised to minimise disruption to local residents.

In the first construction phase, watertight excavation pit enclosures consisting of bored piles or diaphragm walls and back-anchored DSV bases were constructed for the underground stations, initially in successive sections due to the high groundwater levels.

At the top, the excavation pit enclosures were then closed with reinforced concrete covers. The existing soil remained in the enclosure and the railing surface was restored. In the 2nd construction phase, the tunnelling was carried out in quaternary gravel-sand soils under groundwater. The Kaiserstraße tunnel was excavated using a tunnelling machine with a liquid-supported face, with a clear internal diameter of 8.20 metres. The excavation under the covers and the final construction of the stations with distribution levels above the driving level as well as stairs and lifts to the surface and to the platform levels only took place once tunnelling was complete. The overburden was only 4 to 8 metres thick.
The southern branch of the tunnel was excavated conventionally using shotcrete construction under compressed air.

Almost all standard construction methods for specialised civil engineering (sheet piling, bored piles, diaphragm walls, jet grouting, underwater concrete, etc.) were used for this technically demanding inner-city construction project. In addition, a considerable amount of securing and underpinning measures were required, as well as numerous relocations of supply lines, which were carried out together with Zetkon Ingenieure GmbH