The tunnels are part of a £250m project to provide new underground electricity transmission infrastructure.
The project involves the construction of 32km of 4.0-metre and 3.0-metre internal diameter tunnels as well as 14 shafts and four connecting tunnels with associated underground chambers. Main contractor is Costain Skanska.
The wider tunnel is being excavated by a Herrenknecht earth pressure balance (EPB) tunnel boring machine (TBN) and the smaller one by a Caterpillar MP139SE dual mode TBM from Canada. The Herrenknecht is nicknamed Cleopatra and the Caterpillar is Evelyn.
It is Evelyn that has now set a new project record – 55.2 metres in a single 12-hour shift.
Evelyn was delivered to the project in November 2011 and launched from Willesden sub-station in March 2012 to dig 19km of the 32 km tunnels. She is now on the final stretch with just 1,800 metres left to construct.
So far, Evelyn has arrived at seven shafts and one underground chamber, and is due to arrive at the last shaft in early March. To date Evelyn has excavated 17,433 linear metres in London clay, with a volume of 17,1581m³ removed from site.
Other project bests achieved by Evelyn include:
- Best 24 hour day – 98.4 metres (Jan 2013)
- Best five-day week – 363.6 metres (Dec 2012)
- Best seven-day week – 476.4 metres (Dec 2012)
- Best month – 1,422 metres (Jul 2013).
Angus Mackenzie, the tunnel agent working on the project, said: “Evelyn’s performance and reliability has been excellent, with availability continuously in the high 90 percentiles.”
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