Penultimate breakthrough on London Power Tunnels

TBM Edith completed the 6.3km journey from New Cross substation to Kings Avenue in Lambeth in south London, marking completion of four of the five drives for the National Grid project.

Four TBMs have been used for the works. Just TBM Grace remains tunnelling, boring an 11.1km tunnel eastwards from New Cross substation to Eltham, which should be completed in early autumn.

The first, 6.7km drive was completed when TBM Christine broke through in June last year.

In March, the 140-tonne Herrenknecht TBM Christine completed a 2.5km drive in a flooded shaft. As the route to the breakthrough in Crayford passed through a chalk aquifer, there was the risk of high-pressure water flowing into the shaft. By flooding the shaft, the Hochtief-Murphy team was able to balance the water pressure, creating the conditions to allow sealing gel to cure before draining down.

LPT is a £1bn, seven-year project to rewire south London via deep underground tunnels. In total, 32.5km of 3m-diameter tunnels are being built between Wimbledon in south-west London and Crayford in the south-east, which will carry high voltage electricity cables. Phase 1 of the project was completed between 2011 and 2018, and carried the cable circuits north of the River Thames. The new network will be operational in 2027.

Most of the electricity supply in south London is currently transmitted through underground cables, traditionally found just below the road surface. Work to maintain them is carried out at street level and can be disruptive. LPT will enable maintenance work to be carried out without disrupting traffic, residents and businesses and additional cables can be installed in the tunnels to meet future demand.

National Grid says LPT will also provide crucial infrastructure to help the UK energy sector reach net-zero targets.