Milestone for Kriegsstraße street tunnel in Karlsruhe: ZÜBLIN completes ground engineering works

• Züblin Spezialtiefbau GmbH completes eleven excavation pits
• Enormous challenge for construction technology and logistics
• Work on tunnel shell on schedule 

ZÜBLIN has reached an important milestone on the construction site for the Kriegsstraße street tunnel in downtown Karlsruhe. In November, the construction team from Züblin Spezialtiefbau GmbH poured the concrete for the last of 1,251 bored piles for the 1.6 km long tunnel. “We are pleased that we could contribute our wide range of ground engineering expertise to the realisation of this challenging project,” says Michael Rothmund of ZÜBLIN Ground Engineering, who has been with the project from the very beginning.

Technically complex – logistically challenging

The construction consortium responsible for the tunnel shell also includes Ed. Züblin AG (consortium leader) and SCHLEITH GmbH. ZÜBLIN Ground Engineering was entrusted with waterproofing and retaining the excavation pit with overlapping and widely spaced bored pile walls as well as cut-off walls with inserted sheet pile wall. In the past 3½ years, the construction team built approx. 47,000 m² of cut-off walls, completed 20,000 m of bored piles and installed almost 57,000 m of shoring anchors. To seal the bottom of the excavation pit, a total of approx. 34,000 m² of soft gel was injected and extensive jet grouting work was carried out. The production of the soft gel base slab at a depth of up to 20 m was the central ground engineering task and required precision and expertise.

Besides the high groundwater level, the adjacent buildings also presented a major challenge. “Such a large construction site in the middle of the city is truly something special. For the most part, we had to perform our work on the diaphragm wall and the excavation pit at the same time in a very confined space,” reports Michael Rothmund.

The last construction tasks remaining to be developed by the ground engineering team also involved limited space and geometrically challenging excavation pits. “During the installation of the last twelve anchors, we had to reschedule at short notice due to the cramped conditions in the excavation pits,” explains Vanessa Graf, site manager from ZÜBLIN Ground Engineering, “but thanks to the close collaboration among all project participants – both internal and external – all eleven excavation pits were completed ahead of schedule.”

While the team from ZÜBLIN Ground Engineering has fulfilled its mission, the consortium of ZÜBLIN and SCHLEITH is continuing its work on the tunnel shell and the subsequent road construction at full speed. “We are fully on schedule. We have covered 95 % of the tunnel roof and have already laid the asphalt in two sections,” says overall project manager Roman Kühn from ZÜBLIN. For him, the project is heading into its final phase. In July of next year, the consortium will hand over the partially completed tunnel shell with the completed road construction to client KASIG.

The overall completion of the Kriegsstraße street tunnel, part of the Kombilösung public transport infrastructure project to reduce the volume of traffic in central Karlsruhe, is scheduled for the end of 2021. More information is available at: www.diekombiloesung.de.