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£27 million electricity tunnel completed

New subterranean superhighway to power London

From Press releases - 30 June 2016 12:00 AM

27million tunnel completed in London 4.jpg

A new £27million electricity superhighway has been constructed underneath London to boost power supplies in the capital.

A tunnel boring machine, named Fionnuala, has completed a 3km journey between South East London and East London to carry an extra 400 megawatts of electricity into the heart of the capital – the equivalent of powering about 130,000 homes.

The machine broke into an underground chamber in East London last week (June 23) with millimetre-precision nearly two years after launch from a construction site in South East London.

With 50mm to spare, the machine entered the reception chamber with pinpoint accuracy. It is the engineering equivalent of passing through the eye of a needle - and there the metaphor ends because this is a 91-tonne machine which has bored through layers of chalk, clay, gravel and sand up to 30metres below ground.

The machine’s journey underneath London has created a new subterranean superhighway to deliver essential electricity supplies across London, connect substations north and south of the River Thames and meet increasing demand for electricity. The technique avoids months of roadworks in London when the cables are installed, upgraded or repaired.

UK Power Networks, which owns and operates London’s electricity network, has built the tunnel between South East London and East London in partnership with tunnelling experts J Murphy and Sons as part of a wider project. The tunnel adds to the existing network of underground tunnels which deliver power supplies across London.

Nirmal Kotecha, director of capital programme and procurement at UK Power Networks, said:
“London’s power needs are increasing all the time and we are constantly investing in new infrastructure to ensure we maintain reliable electricity supplies. 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.”

Darren Ramsay, from Murphy, said: “I am so proud of the work of our team, spending two years underneath London to help ensure reliable power supplies in the capital, working collaboratively with our client UK Power Networks. Each milestone was successfully negotiated, from the challenges of tunnelling underneath the River Thames, the Jubilee tube line and train tracks running into London Bridge. The final breakthrough in East London will be achieved with minimal disruption to Londoners and the environment. It is testament to the work of our team, successfully achieving break-through despite difficult ground conditions without deviating from the original tunnel line - impressive given the 3km distance, and given that each end of the tunnel was bored nearly two years apart.”

The tunnel is the third and final stage of a three-part tunnelling project to install new 132,000 volt electricity cables along a longer 5.7km route between substations in South East London and the City. The first stage, completed in 2011 with J Murphy and Sons, was a £1.1million 30-metre-long interconnecting tunnel and junction chamber. The second stage was a £14million 2.7km-long tunnel between East London and the City, completed with Morgan Sindall in March 2013.

The tunnel boring machine has progressed at a rate of up to 23-metres per day at depths of between 22 and 30metres below ground. It has successfully negotiated the challenges of running underneath the River Thames, the Jubilee tube line and train tracks running into London Bridge. On the rest of the route it also ran underneath the Docklands Light Railway, Hammersmith and City, Central tube lines as well as train tracks running into Liverpool Street and Fenchurch Street stations.

Now the 2.85-metre-wide tunnel is finished it will be lined with hundreds of brackets to carry 132,000 volt electricity cables, connecting substations between South East London, East London and the City. Work to fit out the new tunnel is due to start in July and last seven months and the new cables are due to go live next summer.

Project fact file: South East London to East London
• The Lovat tunnel boring machine is  7.5-metres long, 3.4-metres diameter and weighs 91 tonnes
• It arrived in South East London in sections in summer 2014 and was assembled underground
• The machine burrows at a speed of up to 23 metres per day
• 37,000metres of 132,000-volt cables will line the tunnel between South East London and East London
• Over a dozen specialist staff worked shifts inside the tunnel
• Miners reached the cutting face by train, taking 30 minutes at the furthest point
• Over 6,000 train journeys within the tunnel
• Over 290,000 man hours completed without any lost injury time
• Over 77,000 tonnes of excavated material have been transported from site
• 99.7 % of surplus material removed from site has been recycled
• There will be extra space in the tunnel to accommodate future cable capacity
• 3,000 concrete rings line the interior of the tunnel from South East London to East London
• Each concrete ring is made of six segments and there are 18,000 segments
• 600 brackets will hold the new electricity cables in place along the tunnel walls

Investing in new electricity infrastructure is a key part of UK Power Networks’ plans for the eight years from 2015. UK Power Networks is investing £500million this year to upgrade and maintain its networks as part of a £4.5billion investment during the eight years to 2023 to keep power supplies safe and reliable for homes and businesses.