UK Power distribution company the National Grid Company celebrated completion of a starter shaft for its giant London Connection project last month.
The 20km tunnel project will carry high-power transmission lines 20m beneath the city.
The finished shaft is one of an eventual seven for the 3.5m i.d. tunnel, which will start to be built later this year.
Tenders will be evaluated and a decision made on the main drive by the end of September.
Designer for the project Brown & Root says the tunnel will run from Elstree in Hertfordshire to St John Wood in London.
Full face TBMs are to used and an anticipated 40m advance of 40m daily is expected. Some 400 000t of London Clay spoil will result, though machines are also likely to have to deal with Reading bed gravels.
The phased project is due for completion in 2004.
The now completed shaft was built by contractor J Murphy. At 25m deep it is not the largest – the deepest shaft will be 40m.
The completed shaft’s diameter is 10.5m.
The remaining shafts will be constructed as part of the main works.
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