The first extension to the Tube network since the Jubilee line in the late '90s is well and truly underway, as Transport for London (TfL) has announced tunnelling has started on the Northern Line extension.
The first of two giant tunnel boring machines, named Helen, began her 3.2km journey to branch out the line from Kennington to Battersea.
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The two machines (the other's called Amy, FYI), were lowered 20m below ground in Battersea in February and now one has set off under south London to create the first of the underground tunnels extending the Charing Cross branch of the Northern Line from Kennington to Battersea Power station, via Nine Elms.
Amy will follow suit in around a month's time.
The Northern Line extension, targeted for completion in 2020, will support around 25,000 new jobs and more than 20,000 new homes. Two new stations are also being created – one at the Battersea Power Station redevelopment and another at Nine Elms.
How the Northern line will be extended (Source: TfL)
Timeline of the Northern line extension:
- 2017 - Main tunnelling takes place
- 2019 - Station fit out
- 2020 - Testing and commissioning; extension in operation
As the 100m-long tunnelling machines make progress, 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 is expected to be excavated by the two boring machines in this way, before the spoil is taken by barge to Goshems Farm in East Tilbury, Essex. There 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 and tunnelling is expected to take six months to complete.
Here's a look at the boring machines before tunnelling began