Light at the end of the tunnel

A seven-year Costain Skanska JV project to make London’s power infrastructure fit for the 21st century is coming to a successful close.

The London Power Tunnels contract saw the JV partners tunnelling for some 32km under the capital, creating what client National Grid describes as an ‘electricity superhighway’ for high-voltage cables to provide increased resilience for the city’s power supplies.

When all aspects of the project are complete in 2018, it will help ensure that London’s growing demand for power can be met over the coming years.

The project involved driving three major new tunnels under London, linking Hackney in the east with Willesden in the west and Wimbledon to the south, with 14 shafts along the route providing access from street level. This represents the longest single tunnelling contract ever let to a single contractor in London.

“Construction of the tunnels was completed in 2015 with the shafts and headhouses fully completed in 2017,” said Costain Project Manager Andrew Hudspith. “We are close to successfully completing the commissioning of the final section of the project which will enable energisation of the full entire network”.

The project saw two tunnel boring machines (TBMs) cutting their way through London’s varying strata at depths of up to 45 metres. Through engagement with local schools competitions were held to allow pupils to name each machine, Cleopatra and Evelyn selected as the winning entries.

 “The project’s challenges were solved via a series of technical innovations, much of it involving prefabrication of multiple elements of the build, from tunnel and shaft segments to cover slabs, beams and access staircases.” Costain has been the key contract partner for the project since 2011, constructing this vital asset in challenging environments. The vast scale of the undertaking is sometimes easy to forget, with the 32km of tunnels crossing 37 existing tunnels. Work was completed without incident, with real innovation in managing and monitoring settlement yielding strong performance across the project.

 “The London Power Tunnels Project is an excellent example of the way in which Costain has been able to play a significant role in successfully delivering new modern energy infrastructure that will allow power to be delivered safely to meet London’s ever increasing demand”.

The client and operator, National Grid, opened the tunnels in an official visit by His Royal Highness the Prince of Wales.  Over 200 kilometres of transmission cables are now energised, which will carry up to 20% of London’s electricity once older networks are decommissioned.