Cologne is built on sand. So constructing the subway calls for a great deal of expertise and maximum effort. Here some impressions of what is currently Germany’s largest inner-city construction project.
Text: Hubertus Tessar, Photos: Fritz Stark
“A Ferrari it’s not,”laughs Gustav Kupkowski. The equivalent of a speedometer on the control panel registers 50 millimeters per minute. No, for all its 1,100 kilowatts, the 76 meter long monster that the man is guiding is certainly not built for speed. He manages ten to twelve meters a day. Which is good progress for a tunnelboring machine weighing over 1,000 tons. Especially considering that it’s not on a Formula One racetrack, but making its way through the ground beneath the city of Cologne.
A new city rail link is under construction, which from 2010 will connect the densely populated south of the city with the main railway station, closing a gap in the local public transport network. “In the past, poor connections to the inner city have meant that many inhabitants preferred to drive,” explains Karl Bücker of Kölner Verkehrsbetriebe (KVB), the client for this project. Traffic jams, noise and exhaust fumes were the result. To increase the pace of public transport, a large part of the 4-kilometer long new line will run underground – in two parallel single-track tunnels. The KVB project manager is delighted, “this will cut journey times from the south of the city to the center by more than half.”
The joint venture led by Bilfinger Berger is also saving time and money by using two identical hydro-mix shields. These special tunnel boring machines are clawing their way through the sandy, stony and very wet subsoil beneath Cologne, stabilizing the ground as they go. More precisely, the drilling head – a rotating cutter wheel with a diameter of 8.40 meters – pushes slowly through the soil. As it advances 174 scraper blades pare away the earth and 19 roller bits break up the larger chunks of rock.