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Published on : Saturday, February 16, 2013
The construction of Crossrail’s Thames Tunnel got off to a flying start thanks to an innovative new tunnel machine launch method developed by Hochtief. This is the first time that the technique, called ‘flying shield tunnelling’, has been used in the UK, having embarked on its maiden ‘flight’ in Cologne, Germany in 2005.
The pioneering method focuses on the very start of tunnelling, when the tunnel boring machine (TBM) cannot yet support itself on newly created tunnel walls.
Traditional methods use a steel support structure and six or seven dummy concrete rings for the machine —a kind of temporary tunnel — that provides a surface for the machine to brace itself against to push forward and begin tunnelling.
The Hochtief patented method uses a hydraulic system to pull the TBM forward. As a result, the temporary tunnel is not needed.
As well as making the launch quicker, this new approach is also safer because it requires less space, making it ideal for constrained sites, like Plumstead.
Sophia, Crossrail’s fifth tunnelling machine, began her journey from Plumstead to North Woolwich earlier this year as part of the construction of a tunnel under the River Thames. The 110 metre long machine is scheduled to drill at an average rate of around 100 metres a week, installing precast concrete segments as rings to form the tunnel lining as it advances forwards.
Passengers in southeast London will benefit from some of Crossrail’s most significant time savings. With Crossrail, the journey from Abbey Wood to Bond Street will be around 20 minutes quicker and passengers travelling to Heathrow will be able to shave around 40 minutes off their journey.