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 onto 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.

Kennington Green cavern

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.

Battersea Station

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


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  1. Harry says:

    I’m trying to work out how a tunneling machine can require a team “of around 50 people needed to operate them”. Might be scope for an interesting article about what they’re all doing some time.

  2. Duncan Martin says:

    Well I assume that they are working 24/7, so there may only be around 10 at any one time.

  3. Melvyn says:

    Given this scheme is a major reason for the separation of the Northern Line into two seperate lines with only trains via the City Branch planned to serve Morden while the West End branch serves this new extension it’s a pity that full upgrade of Kennington Station is not also planned with lifts for full step access and maybe also additional escalators given how passengers who can now make direct journeys will have to change in future .

    I suppose these stations will be similar to those found on the JLE with a wide island platform served by escalators and lifts from platform to booking hall level and then linked to the new development.

    • Sean O'Brien says:

      But they’ll just change over to the other platform as they currently do? There are no steps in the way of the interchange.

      But yes otherwise it is a shame there doesn’t seem to be a plan to make it step free.

  4. Nicholas Bennett says:

    A pity there is not the money for an onwards connection to Clapham Junction.

    • peter feltham says:

      No we are dead broke,after all we have to find a BILLION a month for our so called Foreign Aid.

    • BelleIsle says:

      Clapham Junction was omitted because of the fear that passengers changing from national rail services would overrun the extension from day one. Passive provision has been made for a future extension post Crossrail 2 at which point travel patterns should be different.

  5. Dai says:

    Why do your lightbox images automatically change on? It is infuriating! I like to decide when to see the next picture, not when you THINK I do.

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