Breakthrough for London Power Tunnels transmission project

National Grid’s £1 billion ($1.2 billion) tunnelling and transmission London Power Tunnels (LPT) project has achieved its final tunnelling breakthrough at the Eltham substation in Greenwich.

The last of the project’s tunnel boring machines (TBMs), named ‘Grace,’ successfully broke through after covering over 11km from National Grid’s New Cross substation in Southwark.

The LPT project’s newly installed transmission infrastructure is set to be fully operational by 2026. It aims to bolster and future-proof London’s electricity network in response to the growing demand in the capital and to support Britain’s transition to a net-zero future.

The completion of this section means that all 32.5km of the underground route for the LPT project are now finished. Additionally, the installation of 200km of high-voltage cable, equivalent to the distance from London to Cardiff, is currently in progress between substations at Wimbledon and Crayford.

Alice Delahunty, president of National Grid Electricity Transmission, said: “Our London Power Tunnels project has achieved a lot since it kicked off in 2020, but the final tunnelling breakthrough at Eltham is a particularly remarkable moment.

“This complex engineering endeavour is now really taking shape, with completion of tunnelling now physically linking our sites across South London for the first time and meaning we can move on to the next chapter to progress our vital cabling work.”

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Over the course of the project, approximately 900,000 tonnes of earth were moved, equivalent in volume to half of Wembley Stadium; 99.98% of the waste material generated during the project was diverted away from landfills.

Construction of the tunnels commenced in March 2020, with National Grid’s delivery partner, HOCHTIEF-Murphy Joint Venture (HMJV), managing the tunnelling works.

The LPT project was executed in three sections connecting existing National Grid substations: Wimbledon to New Cross (12km), New Cross to Hurst (18km) and Hurst to Crayford (2.5km). This endeavour involved the use of four TBMs named Christine, Caroline, Edith and Grace.

To aid in the tunneling process, vertical shafts were constructed along the route, ranging in diameter from 9 to 15m and depths of up to 55m. These shafts served as waypoints for the TBMs and will facilitate safe access for maintenance once the tunnels become operational. Headhouses will be built to cover these shafts for future safety.

At the Hurst substation site, a world record-breaking pour of cement-free concrete filled the base of its 55m deep shaft following Christine’s two tunnel drives to Eltham and Crayford.

National Grid’s Bengeworth Road substation on the tunnel route in Lambeth is being constructed without the use of greenhouse gas SF6, making it the first of its kind in Britain and aligning with National Grid’s goal to have SF6-free infrastructure by 2050.

Minister for nuclear and networks, Andrew Bowie, said: “Today’s completion is a huge milestone for the London Power Tunnels project, a superb feat of British engineering that will help future-proof our capital’s electricity network.

“This is part of National Grid’s wider commitment to rewire and modernise London’s electricity network, significantly increasing London’s capacity and energy security for years to come.”