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CROSSRAIL Dry approach to Connaught Tunnel repair Feb 2012
Crossrail News Release
Crossrail has announced a new method for refurbishing the nineteenth century Connaught Tunnel that runs under London's Victoria and Albert Docks and will become part of the new Abbey Wood branch.
Work to the 1km long tunnel under the Royal Docks is to be carried out by Vinci Construction. Crossrail originally planned to strengthen the central section of the tunnel by removing the existing steel linings and back filling the entire section with cellular concrete. These tunnels would then have been enlarged by boring through the concrete to create tunnels that would be large enough for Crossrail trains to pass through.
  • Existing Connaught Tunnel runs under the Royal Docks

    Existing Connaught Tunnel runs under the Royal Docks

  • The tunnel is brick- and steel-segment lined

    The tunnel is brick- and steel-segment lined

But a fresh top-down cut and cover approach has now been announced that involves placing cofferdams in the Connaught Passage between the Royal Victoria and Royal Albert Docks, pumping out the water and creating a dry construction site accessible from above.
Linda Miller, Connaught Tunnel Project Manager said: "The central section of the Connaught Tunnel is in a poor structural condition. To ensure we can undertake the enlargement work as safely as possible we have now decided to drain a section of the Royal Docks and then dig down into the tunnel."

Fig 1. Connaught Tunnel alignment

She added: "This will be the first time the tunnel has been exposed from above ground since its construction in the 1870s. We will be using a similar cut-and-cover approach that was used to build the original tunnel that saw the tunnel constructed first with the docks then built over the top."
Ahead of the refurbishment, which is due to start next year (2013), Crossrail is carrying out an extensive search of the construction area for unexploded bombs from World War Two. The geology of the site is such that devices may have settled a few metres below ground level.
A team of highly trained specialists is currently using armoured vehicles with magnetic equipment to investigate the ground around Connaught Tunnel.
Their work involves sending probes into the ground at 3m intervals, and analysing the results. The dock floor above and around the Connaught Tunnel has already been searched by divers and given the all-clear. The specialists will shortly begin surveying under Connaught Bridge directly above the Connaught Tunnel.

Fig 2. Layout of Crossrail tunnel drives

Connaught Tunnel in the Royal Docks was built in 1878 and was part of the North London Line until 2006. Sections of the existing tunnel, which was shut in 2006, are in need of urgent attention. In 1935, larger ships began scraping the bottom of the Royal Victoria Dock, below which the Connaught Tunnel sits. As part of work to deepen the dock, the central section of the tunnel was narrowed, with brickwork removed and steel segments installed.
This central 550m section of twin running tunnel will now have to be widened, in addition to extensive refurbishment of the entire 1km alignment.
References
Scheduling for success at Crossrail - TunnelTalk, April 2011
Crossrail awards tunnelling contracts - TunnelTalk, December 2010

           

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