This was no lightweight piece of work. 3.4 km subway build cross city underground in Düsseldorf with first trains run on the weekend. Nine years full of challenges are over. A 1300 ton drilling machine milled through the icy surface, ground water pressurized by the Rhine has to be closely observed.3.4 km long, the new Wehrhahn line of which less than 2.3 km is underground with six stations and two above ground stations. Amazing: The engineers have managed to pass the project almost on time.
End of 2007, the North Rhine-Westphalian state capital decided to build new subway line. This subway construction was no day-to-day business for the participating engineering company. Had numerous technical challenges to overcome. So the space available in the Düsseldorf City Center are extremely tight, there is a high ground water level due to its proximity to the Rhine. Historic buildings are extremely sensitive and needed to be protected against shocks.
Part of the Kaufhof was particularly difficult
Most important tunnel tubes had to pass below Kaufhof on the Königsallee. This imposing building with its grade II listed Art Nouveau exterior facade is over 100 years old and accordingly at risk when including a tunnel being drilled.
That was a task for the tunnel experts by Herrenknecht, which have proven themselves even when drilling of the new Gotthard tunnel. The drill with the cute name Tuborine – almost 10 m in diameter and 1300 t heavy gobbled down by the underground. Every day 10-15 m, only 2.3 km in one direction, then back in the opposite direction.
The like employed tunneling shield came to the highly sensitive Kaufhof section in the middle of the city center but not in question. Hard to avoid shocks could have led to goals and thus to the detriment of the statics of the building. “This section has provided us with special challenges,” explained Eng. Ulrich Pöggeler, Managing Director of ZETCON Engineers who were responsible for the complete construction supervision and construction supervision of the tunnel shell construction and dismantling.
The ground beneath the Düsseldorf City Centre was iced up
The engineers are taken almost as at this point, as happened on the ruins of the nuclear reactor in Fukushima. There, the ground was frozen to build a water barrier. In Fukushima, to prevent that contaminated water in the Pacific Ocean flows.
In Düsseldorf, the entire floor was frozen under the Kaufhof to seal the building against ground water and to stabilize the ground.
This ground icing alone took approximately 60 days. In this ice tank a tunnel was constructed then in mining manner within a year in 22 m depth length of approximately 75 m. For large hydraulic excavators with so-called milling drills used, which broke the ground in several sections within the ice body came.
High-precision control system on the facade
500 temperature sensor controlled the layer of ice during this construction phase continuously, to ensure that it is not taut. The ice tanks held with a thickness of 2.5 m over two years. Along with this came a high-precision control system with over 150 individual sensors and prisms on the facade of the Kaufhof used, which covered even the slightest movements of the structures.