A major milestone in the construction of the Northern Line Extension was reached this week with the lowering of two giant tunnel boring machines 20 metres below ground in Battersea, ahead of tunnelling starting in March.
The precision operation required a huge 750-tonne crane to lift the two tunnel boring machines, Helen and Amy, in the shadow of London’s iconic Battersea Power Station.
The two tunnel boring machines will create two 3.2km underground tunnels to extend the Charing Cross branch of the Northern line from Kennington to Battersea Power Station, via Nine Elms Station. Tunnelling will take six months to complete. The extension, targeted for completion in 2020, is the first major Tube line extension since the Jubilee line in the late 1990s.
Both tunnelling machines will now be fully assembled within two 77m long launch tunnels, before starting their journeys towards Kennington next month. When fully assembled, Helen and Amy will each be 100 metres in length.
According to tunnelling tradition, the machines cannot start work until given a name and, following a vote by local school children, were named in honour of the first British astronaut, Helen Sharman, and British aviation pioneer, Amy Johnson, who was the first female pilot to fly solo from Britain to Australia.
After both tunnel boring machines and their gantries are constructed, a conveyor system will be built to take the spoil from the tunnels up to barges on the River Thames. More than 300,000 tonnes of earth will be excavated by Helen and Amy in this way before the spoil is taken to Goshems Farm in East Tilbury, Essex by boat where it will be used to create arable farmland.