The delayed Northern Line extension tunnelling has started with the first tunnel boring machine (TBM) launching on its 3.2km journey.
Two 650t, 100m long TBMs were lowered into 20m deep shafts at the former Battersea Power Station in February. The first, named Helen by local schoolchildren, is creating a 3.2km long, 5.2m diameter tunnel for the Kennington to Battersea extension while the other, Amy, will follow next month.
Tunnelling was originally due to start in summer 2016 but was pushed back six months as modifications were made to the work schedule. It was then due to start last month but slipped to April as readying the TBMs took longer than expected.
A Ferrovial, Agroman and Laing O’Rourke joint venture was selected by London Underground in 2014 for the design and build of the link from Kennington to Battersea. Despite delays Transport for London (TfL) still expects the Northern Line extension to finish in 2020.
As the TBMs push forward almost 20,000 precast concrete segments will be put in place to line the tunnel. Around 300,000t of waste from tunnelling will be taken away by barge on the River Thames and reused to create farmland in Essex.
The Northern Line project is the first major tube extension since the Jubilee line in the 1990s. Tunnelling is already underway by hand at Kennington where the extension connects to the existing Northern Line to avoid the risk of machinery colliding with the tunnels.