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Monster TBM exits early on Groene Hart rail tunnel


TUNNELLING ON the Groene Hart Tunnel in the Netherlands was finished in December after two years, several months ahead of schedule.

The 8km tunnel, including approaches, carries the new high speed railway line connecting Brussels, Rotterdam and Amsterdam, beneath a protected area in the middle of the Netherlands - the Groene Hart or Green Heart (European Foundations Spring 2002).

Bouygues Construction, working in joint venture with fellow contractor Koop, decided to build a single bore tunnel almost 15m in diameter with a central separating wall, as an alternative to two smaller diameter tunnels.

The 14.87m diameter, 120m long, 3,100t monster earth pressure balance TBM was designed and built by French firm NFM Technologies, which is part of the German Wirth group.

With a maximum speed of 40mm/minute, the TBM started work in December 2001 and excavated 7,176m - 1.3M. m 3- of ground in just two years.

Clocking up maximum rates of 16m a day and 616m in a month meant the machine emerged at the exit shaft, in a waterlogged polder, far sooner than originally planned.

After draining the polder, work began to dismantle the TBM in January. The process is expected to take another three months.

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