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Costain-Skanska hands over first tunnel portal to Crossrail

3 October 2011

A Costain-Skanska joint venture has handed over the first major civils contract to Crossrail, the UK’s biggest rail infrastructure project, after completing the construction of the Royal Oak portal, in west London, nearly one month ahead of schedule.

In what is a major achievement for the project team, which had to work in a restricted space surrounded by live rail and tube lines, tunnels, bridges and utilities, including live overhead power lines, the Costain-Skanska joint venture formally handed the completed project to the client at the beginning of September.

Crossrail is a new 118 kilometre high frequency rail route that will run from Maidenhead and Heathrow, in the west, through new twin-bore 21 km tunnels under central London, before forking at Stepney Green for Shenfield near Brentwood and Abbey Wood, in southeast London.

The Royal Oak portal near Paddington, in west London, will be the transition ramp for trains entering and exiting the central London tunnel. Prior to entering the tunnel, trains will traverse along a gradual gradient for several hundred yards. Bordered by the A40 Westway to the north and the Hammersmith and City line and Network Rail to the south, the team had to work in a narrow corridor which was 22 metres wide at its widest point and one kilometre in length, which meant that getting the logistics right in terms of manpower, materials and machinery was critical for the success of the project.

“We were no more than three metres away from the Hammersmith & City line on one side and the A40 on the other, with three bridges overhanging at the side, so space was extremely tight. Another big challenge for us was in mobilising the cast for the diaphragm walls as we needed three cranes and two piling rigs, which is a lot of heavy machinery to have in such a confined space,” said Vicknayson Thevendran, Project Manager for the scheme.

A total of 25,000 m3 of ground was excavated to construct the portal. At the deepest end of the ramp, a concrete headwall was constructed with a pair of 7.24 metre diameter tunnel ‘eyes’ which were created for the installation of steel rings that will support the tunnel opening when the tunnel boring machines break through the headwall.

The Royal Oak tunnel portal is the first of five to be completed on the Crossrail route and will act as an entry point for the tunnel boring machines that will start constructing the Crossrail tunnels next year.

Costain-Skanska secured the job in 2010 as part of an advanced works civils framework contract, which is a four-year programme of works totalling £100million. The joint venture team is also working on a second Crossrail portal at Pudding Mill Lane, near the London 2012 Olympic site at Stratford, which is due to be handed over in 2013. Crossrail services are due to commence from late 2018.