The Northern Line Extension moved a significant step forward recently as the first of two tunnel boring machines, Helen, began her 3.2km tunnelling journey to extend the line from Kennington to Battersea.
Helen, and her sister machine Amy, were lowered 25m below ground in Battersea in February, with the iconic Battersea Power Station offering a powerful backdrop. Helen has now set off under south London to create the first of the underground tunnels that will extend the Charing Cross branch of the Northern line from Kennington to Battersea Power Station, via Nine Elms. Amy will follow in around a month.
“I am thrilled to be able to contribute to this milestone on such an impressive and complex engineering scheme. TBM tunnelling may have just started, but what we are seeing now is the output of more than a year's work of planning and engineering. The Sprayed Concrete Lining (SCL) team has been working hard for almost 12 months digging other areas of the project and making room for the TBM drives that are now underway. I am proud to continue to be part of this great effort”
The extension is the first major Tube line extension since the Jubilee line in the late 1990s.
“The fact that engineering feats of this kind have not been seen on the London Tube for decades makes the project all the more fascinating and challenging. The technical, environmental and logistical nature of the extension is incredibly complex, but one where we are bringing real value by working closely with our client, suppliers, Ferrovial Agroman Engineering Services and the communities nearby. We are firmly focused on delivering this infrastructure that the capital and Londoners so need, as well as ensuring the benefits in terms of skills and employment are also clearly felt by local communities. We look forward to getting Amy safely on her way soon”
As the 100m long tunnelling machines advance forward, nearly 20,000 precast concrete segments will be put in place to form rings to line the tunnels. A conveyor system will then 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 by barge to Goshems Farm in East Tilbury, Essex where it will be used to create arable farmland.
Each machine is capable of tunnelling up to 30m a day with teams of around 50 people operating them. Tunnelling is expected to take around six months to complete.
According to tunnelling tradition, tunnel boring machines cannot start work until given a name. Following a vote by local school children, the machines 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.