A new tunnel could be dug under the Thames to the east of London to carry electrons for the National Grid’s electricity network.

There’s already an electricity cable tunnel under the Thames between Gravesend and Tilbury, but it is more than 50 years old and is coming to the end of its useful life, and the National Grid says that upgrading the cables inside the tunnel isn’t feasible anymore. The proposed new tunnel, large enough for a Central line train to pass through, will replace it and is expected to last at least 120 years.

Typical electricity tunnel (c) National Grid

Construction will be done by a conventional tunnel boring machine (TBM), which will launch from a 41-metre deep shaft dug on the Thurrock side of the river and drive towards the Gravesend shaft. It’s expected that the tunnel boring phase will last around eight months, and although agreements aren’t signed yet, the National Grid expects that the soil dug out of the ground would be removed by barges to a local wildlife sites to help with creating wetland sites for birds.

Two new ‘headhouses’ will also be built at either end of the tunnel at Gravesend and Tilbury. These headhouse buildings needed to connect the tunnel and act as access points for National Grid workers. The headhouses also act as ventilation shafts, as the electricity cables generate heat, so air is pumped from Thurrock through the tunnel to Gravesend to cool it down again.

New tunnel map (c) National Grid

Lee Driscoll, Lead Project Manager, commented: “The Grain to Tilbury project is essential to upgrade the energy network in Kent and Essex to ensure that we can continue to carry more clean energy to homes and businesses, and help the country reach net zero by 2050.

“We are pleased to have now submitted our planning applications and look forward to delivering this important upgrade following their approval.”

The existing tunnel will be decommissioned, but at the moment, they’re not saying how it will be managed afterwards other than through periodic maintenance visits. No, it can’t opened to the public.

More information about the plans can be found on the project website.

Assuming the planning permission is granted by both councils on either side of the river, then work will start later this year, with shafts dug down in 2025-26 and the tunnel boring machine launched in spring 2026.


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  1. David Walters says:

    Make it a foot tunnel too and it could be a solution to the ferry problem.


    • ianVisits says:

      And just how much larger, aka, expensive, would it need to be to accomodate pedestrians safely next to high power cables, and also add all the infrastructure for access and exits at either end?

    • ChrisC says:

      How wide is the river there / how long is the old tunnel?

      Just because there is a tunnel available does not mean it can be used for pedestrians and there is a safe limit as to how long a pedestrian tunnel can be

      Plus what about the costs of installing safe for the public stairs and access and for the emergency services?

  2. Barry Bell says:

    Once the cable tunnel has been dug, why not use the same equipment afterwards to dig a second tunnel. The second tunnel could then have a shuttle
    train installed going backwards and forwards for use by the general public.

    • ianVisits says:

      If you can make the economic case for a shuttle train, then propose it to the planning application.

    • Chris Wood says:

      But it wouldn’t be a question of turning the tunnelling machine round and boring a parallel tube, as the cable tunnel is about 2.5km downstream of both Gravesend and Tilbury.

  3. Martin says:

    Have any that have commented actually looked and seen where the tunnel is planned? Way out of town! How exactly are pedestrians to reach it

  4. St says:

    Tilbury- Gravesend needs a pedestrian tunnel walkway. It’ll be great if the government can commission a fair feasibility study especially as the highway got canned and the ferry service is now at risk. The crossing is essential services for both communities and takes a lot of cars off the road, off Dartford and Blackwell tunnels.

  5. Andy T says:

    I’ve often thought running the Tilbury line to Gravesend would have been good, but that would have needed to have happened many years ago, the number of people using X80 and Ferry combined wouldn’t fill one carriage.

    Using the build it and they will come philosophy, the KenEx could be the answer, it would perform the same basic function while serving more places.

    Light rail or Tramways are more cost effective and practical in situations like this

  6. Hugh Levinson says:

    Surprisingly, the drift velocity of electrons in a wire is only about a few meters per hour. And, as the grid is ac (alternating positive and negative) at 50 Hz, the electrons won’t actually travel through the tunnel, just shuffle backwards and forwards a fraction of a mm 50 times a second.

    I think this is correct!

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