The final section of a £1 billion tunnel has been completed under south London, when a tunnel boring machine (TBM) emerged into the Eltham substation.
TBM breakthrough (c) National Grid
The 11km long tunnel will eventually carry electricity cables and makes up part of the National Grid’s London Power Tunnels (LPT) project. When fully operational, it will replace a maze of cables running under London’s streets, which are wearing out and need replacing, but rather than digging up loads of roads, the National Grid has opted for a deep tunnel instead.
Construction of the tunnels began in March 2020, and tunnelling was carried out in three sections between existing National Grid substations:
- Wimbledon-New Cross (12km)
- New Cross-Hurst (18km)
- Hurst-Crayford (2.5km)
The last of the project’s TBMs, ‘Grace’, broke through last week, having been tunnelled over 11km eastwards from National Grid’s New Cross substation in Southwark.
Breakthroughs previously took place at Eltham in June 2022, Wimbledon in July 2022, Crayford in January 2023 and Kings Avenue in April 2023.
London Power Tunnels Map (c) National Grid
All 32.5km of the project’s underground route are now complete, with 200km worth of high voltage cable now being installed between substations at Wimbledon and Crayford.
Vertical shafts ranging between 9-15m in diameter and up to 55m in depth were constructed along the route, serving as waypoints for the TBMs, and helping project teams safely access the tunnels for maintenance now and when operational in the future (headhouses will be built to cover the shafts for safe future use).
The Hurst substation site recently saw a world record-breaking pour of cement-free concrete to fill the base of its 55 metre deep shaft following the two tunnel drives to Eltham and Crayford.
In another first for LPT, National Grid’s new Bengeworth Road substation on the tunnel route in Lambeth is being built free from greenhouse gas SF6 – the only one of its kind to date in Britain and part of National Grid’s ambition for its infrastructure to be SF6-free by 2050.
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.
“The outstanding effort by our project teams and suppliers is strengthening London’s electricity network and making sure it safely, reliably and efficiently powers homes and businesses in the capital for years to come.”
The LPT project’s newly installed transmission infrastructure is due to be fully operational by 2026.
https://www.ianvisits.co.uk/articles/new-south-london-tunnel-completed-with-tbm-breakthrough-66229/
