Tunneling for the Northern line extension is due to start in March, it has been announced.
Two French built 650-tonne tunnel boring machines will create two 3.2km underground tunnels to extend the Charing Cross branch of the Northern line from Kennington to Battersea, via Nine Elms.
Each machine is capable of tunneling up to 30 metres per day with teams of around 50 people needed to operate them. The work is expected to take around six months to complete. As they advance forward, nearly 20,000 pre-cast concrete segments will be built in rings behind them.
As is traditional, the TBM’s are being given female names, in this case Helen and Amy 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.
The machines will tunnel at depths of 26 metres for six months, excavating more than 300,000 tonnes of earth. This will then be passed along conveyors before being loaded on to barges and taken to Goshems Farm in East Tilbury, Essex, where it will be used to create arable farmland.
In addition to the TBMs, a number of works are going on elsewhere to create new ventilation shafts, and the junction to link the new extension to the existing Northern line.
Last November, they completed the first part of the connection with the existing loop, which is being called the over-dig as it is the excavation dug at the top of the existing tunnel.
Since they have been propping up the existing tunnels in order to work on the new junction step plate cavern.
As well as two new tunnels, two new stations are being created.
One at the heart of the Battersea Power Station redevelopment. The excavation has been completed, and two starter tunnels are under construction to launch the TBMs from.
The second station will be at Nine Elms to the east. The piling works which form the structure of that station are now complete. Excavators have now begun to dig below street level to reach the base of the future station.
The extension is due to open in 2020.
Photos by TfL