To deliver Crossrail services to Abbey Wood, a new tunnel was built underneath the River Thames between Plumstead and North Woolwich.
The Thames Tunnel stretches for almost two miles, about 15 m below the existing river bed. It is the only point where the Crossrail route crosses the River Thames.
The Thames Tunnel section of Crossrail will help to significantly improve connections between southeast London and the rest of the capital when it opens in 2018. As a result of the new link, journeys times will be cut by up to half from Abbey Wood to Canary Wharf, Bond Street and Liverpool Street.
Did you know?
Twenty-three tunnels currently cross underneath the River Thames. These are used for a variety of purposes including road transport, Tube lines and utilities. The last tunnel to be constructed under the Thames was built in 2009 for the Docklands Light Railway Extension to Woolwich Arsenal.
Constructing the Thames Tunnel
The Thames Tunnel has tunnel portals at either end. These portals, at North Woolwich and Plumstead, mark the entry and exit points from the tunnel.
Construction of Plumstead Portal began in 2011. The portal sits right next to the North Kent Line railway tracks which runs up to 16 trains per hour. Our Thames Tunnel team worked extremely closely with Network Rail throughout construction of the portal to ensure that there were no impacts on those services. The portal was completed in late 2012, enabling the launch of the drives first TBM, Sophia, in January 2013.
The construction of North Woolwich Portal began in early 2012 in order to receive the first tunnelling machine in 2014.
Meet our machines: Mary and Sophia
Mary and Sophia, the two tunnelling machines which completed the Thames Tunnel, were named after the wives of Isambard and Marc Brunel who constructed London’s first Thames Tunnel over 150 years ago.
The machines are different to the tunnelling machines that were used elsewhere on Crossrail. Known as ‘slurry’ machines, they are specially equipped to deal with the chalk, flint and wet ground conditions in southeast London.
As part of the tunnelling process, the excavated soils are pumped out as liquid slurry to a special site treatment plant at Plumstead. The slurry is separated into sand, gravel, water and chalk. The chalk comes out in ‘cakes’ or slabs of filtered chalk particles.
One feature of the Thames Tunnel project was that only 1 TBM could be driven at any one time. This was due to power and water constraints as well as limitations on the extent of muck that could be processed and removed from site.
The machines undertook four individual tunnel drives between them – two between Plumstead and the Woolwich station box; and two beneath the Thames from Woolwich box to North Woolwich Box.
Prior to Sophia reaching Woolwich Box, the machines had to overpass the existing DLR tunnels at Woolwich. At its closest point, the tunnels run within 2m of the DLR tunnel.
First stop - Woolwich
The first stop for the two TBMs was at Woolwich Station – a pre-prepared box constructed by Berkeley Homes as part of the redevelopment of the Woolwich Arsenal. After just over 1km of tunnelling, Sophia and Mary broke through into the station box in May 2013 and August 2013 respectively.
During the tunnel construction, the Woolwich station box was an important staging post for the 1,000 tonne tunnelling machines. The machines underwent maintenance here within the box before being dragged through, secured into the launch chambers and re-starting their journeys – this time heading underneath the Thames before breaking through into the pre-constructed tunnel portal in North Woolwich.
Tunnelling was completed in May 2014 and both Sophia and Mary were dismantled and removed from North Woolwich Portal.