One of the tunnelling machines in London’s major Crossrail project is preparing to start the drive underneath the River Thames, while another has reached Woolwich, in south east London.
Crossrail is currently the largest construction project in Europe.
The 1,000 tonne machine Mary, which started its journey from Plumstead in May, has broken through into the station box at Woolwich, marking the half-way point of tunnelling south of the river.
During the three-month journey, Mary has excavated almost 110,000 tonnes of material and installed 811 concrete rings to line the inside of the tunnel.
The second machine, Sophia, which reached the Woolwich box in May, is being prepared to start on the second leg of the journey underneath the Thames to North Woolwich.
It is planned that passengers in south east London will benefit from some of Crossrail’s most significant time savings. With Crossrail, the journey from Abbey Wood and Woolwich to Bond Street is expected to be at least 15 minutes quicker, and passengers travelling to Heathrow Airport will be able to save around 40 minutes of their journey.
Sophia and Mary are constructing the Thames tunnel, which will run from Plumstead, via Woolwich and underneath the Thames to North Woolwich. They are different to the tunnelling machines being 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.