The tunnel portals will act as an entry point for the tunnel boring machines that will construct the Crossrail tunnels and in future will provide an entrance and exit for trains to the underground sections of Crossrail.
Construction of Crossrail’s tunnels will get underway in spring 2012 when the first tunnel boring machine is launched from Royal Oak. This will be followed by the launch of further TBMs to construct the remaining tunnels for the new Crossrail service.
Construction of Royal Oak Portal was completed nearly one month ahead of schedule.
Ailie MacAdam, Crossrail Central Section Delivery Director said: “Crossrail has now reached its first tunnelling milestone with the completion of Royal Oak Portal. Work is now underway to prepare for the arrival of the tunnel boring machines ahead of tunnelling commencing in spring 2012.”
Construction of Royal Oak Portal got underway in January 2010. The portal has been built within a narrow corridor at Royal Oak, bordered by the A40 Westway to the north and the Hammersmith & City line and Network Rail lines to the south.
The works comprise a massive ramp structure that will take the Crossrail tracks from ground-level down into the underground tunnels. A total of 25,000 m3 of ground was excavated to construct the tunnel portal with the excavated material re-used at construction sites in London.
At the deepest end of the ramp, a concrete headwall was constructed with a pair of 7.24m diameter tunnel ‘eyes’ created for the installation of steel rings. The tunnel ‘eyes’ mark the exact location of where the tunnel boring machines will commence tunnelling at Royal Oak. The tunnel eyes and rings have an important role to play in supporting the tunnel opening when the TBMs break-through the headwall.
The Paddington New Yard site, containing both the Royal Oak portal and Westbourne Park worksites, has now been handed over to the contractor undertaking construction of the Crossrail tunnels between Royal Oak and Farringdon. The contractor has begun to mobilise on-site ahead of tunnelling starting next spring and will also undertake the assembly of the tunnel boring machines at Westbourne Park.
Prehistoric animal bones were uncovered by archaeologists during excavation for the portal. The remains included those of the Auroch, a large ancestor of modern cattle and their discovery is of scientific importance. The prehistoric bones are now being studied before they are incorporated into the Natural History Museum’s permanent collection.
A total of five tunnel portals will be constructed for Crossrail at Royal Oak to the west of Paddington, Pudding Mill Lane near Stratford, Victoria Dock and North Woolwich in the Royal Docks and Plumstead near Woolwich.
Main construction at Pudding Mill Lane Portal is now underway with enabling works progressing at North Woolwich and Plumstead portal sites. Construction of Victoria Dock Portal will get underway in autumn 2012.