Northern Line Extension


Northern line TBMs dropped in

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.


Northern line extension tunnelling to commence in March

The Mayor of London has announced that tunnelling to create an extension of the Northern line between Kennington and Battersea will begin in March.

Sadiq Khan confirmed news of tunnelling for the first major Tube line extension since the 1990s as two gigantic tunnel boring machines were unveiled in Battersea. The two 650-tonne machines, each the length of a football pitch, will create two 3.2km underground tunnels to extend the Charing Cross branch of the Northern line from Kennington to Battersea, via Nine Elms.

According to tunnelling tradition, the machines cannot start work until given a name and, following a vote by local school children, the machines are being named 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 two tunnel boring machines were built by NFM Technologies in Le Creusot in central France. They were shipped to London earlier this year and reassembled in Battersea. Each tunnel boring machine has a rotating cutterhead at the front which is pressed against the tunnel face by hydraulic cylinders. A series of trailers behind house all the mechanical and electrical equipment and a conveyor belt removes the earth.

The machines will undertake two individual tunnel drives at depths of up to 26 metres to construct the 5.2 metre diameter east and westbound tunnels. Each machine is capable of tunnelling 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.


Northern line extension tunnel drive delayed

The tunnel drive for the Northern line extension has been delayed by more than six months. It will now start in early 2017. The tunneling machines were revealed recently following their construction in France. They are set to be dismantled before transport to London.

Despite the delays, Transport for London have been keen to advise that the delay will not impact the expected opening date in 2020.

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