Costain and National Grid recently celebrated a major milestone on the London Power Tunnels project after Tunnel Boring Machine (TBM) Evelyn broke through at Kensal Green, bringing to an end the tunnel construction phase of the longest single tunnelling contract in London.
The tunnels are part of a £1 billion project to provide an easy to maintain underground electricity superhighway, and to ensure London has sufficient transmission infrastructure to support future energy demand.
Evelyn was delivered to the project from Canada in November 2011 and launched from the Willesden sub-station in March 2012. Almost three years to the day since her launch, TBM Evelyn broke through into the shaft at Kensal Green on Wednesday 11th March after completing 19km of tunnelling at an average depth of 30 – 35 metres.
While the new 118km Crossrail route includes 44km of tunnelling work, the project has had eight TBMs at its disposal. By contrast, at 32km, the LPT project has relied on just two TBMs, a 4.0mID Herrenknecht earth pressure balance (EPB) TBM and a 3.0mID Caterpillar MP139SE dual mode TBM, nicknamed Cleopatra and Evelyn respectively by local schoolchildren.
“To complete 19km of tunnelling with just one machine with no significant breakdowns, and an availability rate in excess of 95%, is a real achievement for Evelyn and for everyone involved who kept her going,” said Angus Mackenzie, Costain Tunnel Agent on the LPT Project.
Angus added: “Before we started, we sent some of our team over to Canada to advise the TBM manufacturer and they really listened to our specifications and what we wanted to achieve. Evelyn’s performance and reliability has been superb. Inspecting the cutting head after she broke through was impressive as it looked almost brand new.”
During her journey, Evelyn has arrived at six shafts and one underground chamber, excavating over 19,000 linear metres of London clay with a volume in excess of 187,000m³ and has broken shift and project records every step of the way.
Evelyn will now be thoroughly cleansed and packed away, a job that will take a team of 20 people around three weeks to complete.
Meanwhile, the LPT project now moves into the next phase of its construction, which includes the construction of head houses and the fitting out of the tunnels before the cables are installed and energised. The project is expected to be completed in September 2017, a year ahead of programme, serving to reinforce the High Voltage grid across the whole of London.