400 m tunnels beneath the station
Two new underground ducts will be installed at depths of up to 2.60 m for this purpose. Each tunnel has a total length of around 400 m. The first tunnel has already been completed. Since the foundations of the adjacent existing structure do not extend far enough into the ground for the new construction, Stump-Franki used the jet grouting or “Stump jetting” method on both sides along the entire length of the tunnel to create the underpinning for the foundations. The individual foundations, which were subjected to high loads due to the roof construction of the station, had to be underpinned with almost no subsidence. In some cases, it was necessary to jet grout floor slabs into the soil to brace the underpinning bodies against each other. Planning for the second tunnel is currently underway.
A solution for complex construction site logistics
The ground surface could only be reached with electrically operated machines after 400m. The complex logistics created a number of challenges, which were overcome thanks to the excellent and close cooperation between all the companies involved on the site. The cramped conditions, the aging building fabric and the lack of documentation on the existing structures of the central station meant that the work had to be adapted to the actual geometric situation at short notice.