Rhine Utility Tunnel (Germany)
To ensure that the power network in the greater Cologne region is ready for the needs of the future, a utility tunnel has been built below the Rhine, connecting the new Niehl 3 power plant to communities on the far side of the river. Electrical power and district heating are transported across to the eastern bank through a roughly 650 metre-long tunnel, and embedded in 1,300 cubic metres of Powercrete.
It took around seven weeks for “Marion”, as the tunnel excavator was called, to dig out the passage 8 to 12 metres beneath the riverbed. In all, 450 truckloads of soil and stone were excavated. Marion's drilling head is enormous, with a diameter of 3.4 metres and weighing roughly 100 tonnes, and can work effectively even in saturated soil. “We had no idea what to expect – large boulders or massive layers of granite,” said chief engineer Jonathan Trosdorff of SONNTAG Baugesellschaft. “But, we are more than satisfied with the average of 16 metres daily drilling progress we achieved.”
Directly behind the excavator, 161 steel-reinforced concrete pipe sections were laid to form the tunnel. Each section is 3.4 metres in diameter, 4 metres long, and 30 cm thick. Inside, two district heating pipes, one natural gas line and a conduit with space for six 110-Kilovolt power transmission and fibre-optic cables have all been embedded in 1,300 cubic metres of Powercrete, a patented, highly heat conductive specialty concrete from Heidelberger Beton. It's high thermal conductivity allows heat to be conducted away from the power lines, efficiently reducing transmission temperatures, thereby increasing the efficiency of the cables.
“This was the largest-ever volume of Powercrete used in a single construction project,” said Jens-Peter Müller, Project Manager for the Rhein-Ruhr area at Heidelberger Beton, a subsidiary of HeidelbergCement. “The challenge was to maintain constant quality along the entire supply chain – from production to delivery to installation of the pumping stations.” From Monday to Friday, the Powercrete was pumped in, non-stop from 6am to 6pm. Two mobile pumping stations were used, one at each end of the tunnel, each manned by four employees working in two shifts. “Laying the roughly 450 metres of pipe and 250 metres of hose was difficult given the low ceiling,” explained Torsten Liefländer, Concrete Pumping Specialist at Heidelberger Beton. “Eight employees from Heidelberger Betonpumpen were always on site.”
Detlef Wisbar, General Manager of Heidelberger Betonpumpen, added: “It was a very challenging job. Thanks to the excellent level of communication and coordination with the builder, we were able to lay between 100 and 150 cubic metres of product on peak days. This is an achievement we can be very proud of.”
