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National Grid’s London Power Tunnels breakthrough completes the project’s tunnelling activity


On September 30 th, 2023 the National Grid’s EUR1.15 bn (GBP1 bn) London Power Tunnels (LPT) project has achieved a major milestone with its final tunnelling breakthrough at Eltham substation in Greenwich. 

The last of the project’s 140-t TBMs named Grace, broke through on Saturday 30th September at Eltham site , having tunnelled over 11km eastwards from National Grid’s New Cross substation in Southwark.  

All 32.5km of the project’s underground route - at depths of up to 60m under seven South London boroughs - are now complete, with installation of 200km worth of high voltage cable – enough to stretch from London to Cardiff – already underway between substations at Wimbledon and Crayford.  

In total the project will have shifted 900,000 t of earth with 99.98% of waste material diverted from landfill.  

The LPT project’s newly installed transmission infrastructure is due to be fully operational by 2026, with the aim of reinforcing and future-proofing London’s electricity network – and supporting Britain’s transition to net zero – as demand in the capital grows.  

Construction of the tunnels began in March 2020 with the tunnelling works undertaken by National Grid’s delivery partner Hochtief-Murphy Joint Venture (HMJV).  

Tunnelling on the LPT project was completed in three sections between existing National Grid substations – Wimbledon-New Cross (12km); New Cross-Hurst (18km); and Hurst-Crayford (2.5km) – with the help of four TBMs named Christine, Caroline, Edith and Grace. Breakthroughs previously took place at Eltham in June 2022 (TBM Christine tunnelling from Hurst), Wimbledon in July 2022 (TBM Caroline tunnelling from Kings Avenue), Crayford in January 2023 (Christine again tunnelling from Hurst) and Kings Avenue in April 2023 (TBM Edith tunnelling from New Cross).  

Five 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 m deep shaft following Christine’s 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.  

Please click here and uk/80 for the tunnelbuilder archive. For more information about the LPT project please visit https://www.nationalgrid.com/. 40/23.