23 November 2011

Work to create a new level of resilience for London’s electricity supply is well underway as Costain continues to build the shafts and tunnels for the London Power Tunnel (LPT) project.

Costain is responsible for the civils work for the LPT project, a major project for National Grid to create tunnels that will house a new generation of 400kV electricity cabling. A tunnel will run from Willesden in the west of the capital via Kensal Green to Hackney in the east. From Kensal Green another tunnel will be driven south to Wimbledon.

There are a total of 14 shafts, of which four have been completed with the next four currently being dug at a rate of around one metre a day. The last shaft will be completed in early 2012 and they will all reach depths of up to 40 metres. At the foot of the three launch shafts, launch tunnels are dug to act as the starting points for two tunnel boring machines (TBMs) to begin cutting their way through 32km of routes under the capital. (The tunnels are a mixture of 4m and 3m internal diameter).

Headhouses that will contain mechanical and electrical equipment are being constructed atop all the shafts.

Around 90% of the ground through which the tunnels will be driven is London clay, the ideal material for tunnelling due to its stability and ease of cutting.

The first TBM arrived in the UK in mid September and has been lowered into the launch shaft at the National Grid site in Eade Road, Haringey, ready to start digging this month. Tunnelling is expected to be complete in 2014.

National Grid describes the tunnels as ‘a new subterranean electricity superhighway’.

Given the congestion under central London’s streets caused by existing utilities and Tube tunnels, the new routes have been carefully planned to avoid these obstructions and to minimise settlement on these routes. However, says Costain’s Tunnelling Operations Director, Stephen Meadowcroft: “One of the key challenges is to liaise with all the third parties involved well in advance of any tunnelling.”

The 4m TBM has been named 'Cleopatra' after a competition to choose a suitable name was held at the local cub scout group close to the Eade Road site.

Cub scouts have already visited the site to see ‘their’ TBM. “With visits like this we can show youngsters first-hand how our work makes life as we know it possible,” said National Grid Head of Cable Tunnels, David Luetchford.

“Hopefully some of our visitors may even be inspired to pursue a career in engineering when they are older.”

 

Ends