29 August 2013

The latest milestone in Costain’s £200 million contract on National Grid’s London Power Tunnels project, which is being constructed with Skanska, has been reached eight days ahead of schedule.

On 15 August tunnel boring machine (TBM) Evelyn broke through into a pre-prepared shaft at Wimbledon, southwest London, completing a 3km-long drive from Wandsworth in just four months. It completes the latest stage in the creation of 32km of tunnels being built to house a new generation of 400kV electricity cables under London.

“This is certainly the safest and the quickest tunnelling contract I’ve ever worked on,” said Angus Mackenzie, Tunnelling Agent. “To date, in over 10.5 km of 3m internal diameter tunnel constructed we have incurred only one minor LTI (lost time injury) and have increased our productivity levels to being able to maintain a consistent 60-plus metres per day.”

Extensive planning and a robust preventative maintenance regime were key, along with a very positive behavioural safety culture amongst the entire site team. Said Angus: “We made sure we had identified and analyzed where previous shortcomings had occurred throughout the system and made modifications to ensure they didn’t happen again.”

One of the biggest technical challenges on this drive was a curve in the tunnel alignment that had a tight 22.5 metre radius. “This gave us issues with the pit bottom as the drive shaft was centred on this curve but, using a combination of experience and new ideas, we were able to design around this,” said Angus.

Lennart Stenman, Construction Director, praised Angus and his “very organised” team: “They’ve done a great job completing eight days ahead of programme, managing the operational and technical aspects of the job safely.”

Evelyn is now being dismantled and split up into her principal component parts to be inspected and refurbished ready for her next and final drive on this project: 9km from Wandsworth to Kensal Green in northwest London – this is the longest drive on the 3m id section of the project and takes the tunnel under the River Thames. This will begin at the end of October and is due to be completed by the end of 2014.

Meanwhile Evelyn’s ‘sister’ TBM, Cleopatra, is hard at work on the contract’s other 13km tunnel which runs from St John’s Wood in the west of the capital to Hackney in the east. Cleopatra has recently begun her second drive from the Eade Road drive site in Haringey to Hackney.

The contract is due to be complete by 2014, with full energisation of the new cables planned by November 2018.

Ends