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Preparing the ground

Tunnelling work over 47km is proving a major challenge in the construction of German Railways new high speed line between Cologne and Frankfurt.

The £2bn project will enable trains to travel at up to 300k/h, slashing travel times between the cities from over two hours to under an hour.

The difficulty has been in the ground conditions. Many of the 30 tunnels have been driven through relatively soft rock, some less than 5m below the surface, making stability a top priority for Putzmeister.

A combination of varying geology and programme constraints forced Putzmeister to employ several different placement methods during the project.

In the 3.3km long Dernbach Tunnel, two truck mounted pumps were used to fill the 12.5m long vault formwork sections, with the base formwork filled by mechanical distributors attached head-first below the formwork wagon.

An environmentally sensitive area meant that extremely careful tunnelling methods had to be use constructing the Montabaur tunnels. Lowering groundwater levels was not permitted, so shotcrete was used to ensure the tunnels could be constructed as water resistant structures.

Delays in mining the 2,765m long Niederhausen tunnel meant the original plan to deliver ready mixed concrete via wagons was discarded in favour of a combination of wagons for concreting the vault and long distance delivery for concreting the base. A 150mm diameter delivery line was used to pump 50,000m 3ofconcrete up to 1.4km at a pressure of up to 120bar.

Putzmeister is also providing concrete for the construction of 18 large valley bridges, using truck-mounted pumps with vertical placing booms with a reach of up to 52m. The line is scheduled to open in May 2002.

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