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Page 13 Contractors World - UK & Ireland Vol 1 No 6

to it. These will incorporate steel rings and support the tunnel opening when the TBMs break through the headwall and help protect the valuable TBM cuter heads from damage.

Royal Oak Portal was designed by Capita Symonds. Initial enabling works for the portal got underway in January 2010 with main construction commencing in April 2010. The works were undertaken by a joint venture comprising Costain and Skanska.

London Underground Pump Chamber

As part of the works, it was necessary to build a pump chamber for London Underground, to replace one which previously operated at the portal site.

The new pump chamber is made up of two shafts – one 12 m deep and the other 8 m deep – joined by a 40m long connectng tunnel.

The 1.2 m diameter connectng tunnel was dug with a pipe jack to push specially designed pipes through the ground. Material in front of the pipejack was excavated by a grab and fed back via a conveyor belt as the machine is shunted forward and the tunnel is dug. The ring formed around the pipe was then flled with a grout mixture to minimise any ground setlement.

With the tunnel complete, a series of pumps will be installed to remove water from the Westbourne Park area and discharge into a sewer on the higher level Alfred Road. This is the frst tunnel to be built on Crossrail using this method.

Tunnel Works

Once complete, Crossrail will dramatically cut journey times for travellers in south east London. From Abbey Wood, Crossrail will reach Canary Wharf in 11 minutes, Liverpool Street in 17 minutes, Totenham Court Road in 23 minutes and Heathrow in just 51 minutes.

To construct the 21 km of twin-bored tunnel required for Crossrail, eight tunnel boring machines will be required and

will undertake ten individual tunnel drives to construct the 6 m diameter rail tunnels. The frst two TBMs will launch from Royal Oak in spring 2012.

Earl ier this year, Herrenknecht AG was selected by the major tunnel l ing contractors to build the first six tunnel boring machines for Crossrail.

Construction of the Thames Tunnel is being undertaken by a Joint Venture comprising Hochtef Constructon AG and J Murphy & Sons Ltd who have selected

Job almost completed as a variety of hire plant helps put the fnishing touches in place, prior to handing over to the tunnel contractors.

Working alongside live tracks and under limited space was a challenge

As excavatons take place, the gantry crane can be seen in the background. Photo: Marcus Rowland

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