Costain is involved in the construction of 32 kilometres of four- and three-metre internal diameter tunnels, 14 shafts, and four connecting tunnels with associated underground chambers. The team have so far completed 11 shafts and have achieved 750,000 man-hours with no reportable accidents.
The four-metre tunnels are being driven by a Herrenknecht earth pressure balance (EPB) tunnel boring machine (TBM. The three-metre tunnels are bored by a Cat/Lovat dual mode TBM from Canada. The TBMs have been named respectively Cleopatra and Evelyn by local schoolchildren.
Costain won the £220m contract in 2010 to build the new high voltage electricity cable tunnels between Hackney and Willesden (via St John’s Wood) and Kensal Green and Wimbledon.
TBM Evelyn has dug its way to its first destination, a pre-prepared shaft deep below National Grid’s Channel Gate Road offices after beginning its journey from Willesden Substation earlier this year.
Evelyn is digging 19km of the 32km London Power Tunnels project. Cleopatra is digging the other 13km of the route and is approximately 1km away from her launch site in Haringey. Tunnelling work is scheduled for completion in 2014.
Project manager Andy Firth said: “We are delighted to have reached these milestones for the London Power Tunnels. We are making good progress on this flagship project for National Grid which will help to meet London’s growing demand for electricity in the years to come.”
David Luetchford, the National Grid’s head of cable tunnels, said: “The breakthrough represents another major step towards the completion of this vital project. Our breakthrough at Channel Gate Road is just one part of a much bigger story which involves us deploying the best talent and technology available to help ensure the lights stay on.”