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The Gallery | Light at the end of the (power) tunnel

Tunnelling on the new £27M London power tunnel, the new “electricity super highway”, has been completed underneath London.

The tunnel boring machine (TBM), named Fionnuala, has completed a 3km journey between South East London and East London.

The tunnel will carry an extra 400MW of electricity into the centre of the capital, the equivalent of powering about 130,000 homes, according to owner UK Power Networks.

Tunnelling contractor Murphy said that the machine broke into an underground chamber in East London with millimetre-precision nearly two years after launch from a construction site in South East London.

The 91t machine has bored through layers of chalk, clay, gravel and sand up to 30m below ground, said Murphy. The company added that the route has taken the TBM underneath the River Thames, the Jubilee tube line and train tracks running into London Bridge. It has also run underneath the Docklands Light Railway, Hammersmith and City and Central tube lines as well as train tracks running into Liverpool Street and Fenchurch Street stations.

The 2.85m wide tunnel will now be lined with hundreds of brackets to carry 132,000V electricity cables, connecting substations between South East London, East London and the City. UK Power Networks said that work to fit out the new tunnel was due to start in July and last seven months, with the new cables due to go live next summer.

“London’s power needs are increasing all the time and we are constantly investing in new infrastructure to ensure we maintain reliable electricity supplies,” said UK Power Networks director of capital programme and procurement Nirmal Kotecha. “This essential project will increase the resilience of electricity supplies for residents and businesses for years to come.

“By working deep underground with the Murphy specialist team, we were able to avoid digging up roads along the entire route, helping keep the impact of this major project to a minimum.”

Project fact file: South East London to East London

  • The Lovat tunnel boring machine is 7.5m long, 3.4m diameter, weighs 91t and burrows at a speed of up to 23m per day
  • The 2,965m tunnel comprises rings of six segments each weighing 750kg. There are 17,790 segments in total
  • Over 2,600t of cementitious grout has been injected behind tunnel linings
  • Over 77,000t of excavated material has been transported from site with 99.7% of surplus material recycled
  • Miners reached the cutting face by train, taking 30 minutes at the furthest point
  • The tunnel crossed under ‘live’ operational Jubilee lines with no settlement, plus crossed under the Thames
  • The team carried out three ‘free-air’ tunnel boring machine interventions to inspect the cutterhead, a process that takes four days and nights, replacing the teeth and picks to work at maximum efficiency
  • 37,000m of 132,000V cables will line the tunnel between South East London and East London
  • There will be extra space in the tunnel to accommodate future cable capacity.




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