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Tunnelling Tales From 'The Front Line'

1 April 2014

Costain’s experience in building London’s next generation of underground power tunnels for National Grid has been detailed in a presentation to its peers.

Project Manager, Andy Firth, was one of two speakers presenting ‘Building London’s Electrical Super-Highway’ to members of the British Tunnelling Society at the Institution of Civil Engineers’ in London.

The Costain Group is involved in a multi-year programme worth £250 million to drive 32km of tunnels under the capital to assist National Grid in ensuring the continuity and upgrade of electricity supplies to the city’s seven million residents and organisations.

Andy was joined in his presentation by John Trounson, Senior Project Manager for National Grid Cable Tunnels.

The presentation, in front of more than 200 tunnelling and engineering professionals, took the format of setting out the scope of the project and sharing the knowledge and expertise that Costain has gained in the course of the project.

“We explained the business case, the scope of the project and gave an overview of what we had done in the last three years,” said Andy. “We set out what had been achieved, the obstacles we’d faced and overcome and shared elements of our learning and best practice.

“The presentation was well received and there were a number of quite challenging questions posed at the end varying from procurement strategy to performance and efficiency of the tunnelling equipment.”

And although much of the tunnelling operations have been in London clay, the material favoured by tunnellers due to its stability and the ease with which it can be cut, there had been instances of less stable, water-laden strata that have had to be negotiated.

Andy also regaled his audience with an example of the flexible thinking that had been required to allow the Cleopatra tunnel boring machine (TBM) to negotiate an underground curve too tight for its articulation on entry to the shaft at the St John’s Wood Substation shaft.

The TBM was placed on an innovative articulated mobile cradle. It then underwent a controlled pull using winches and CCTV system to drag it along 100 metres of pre-built curved adit into the pit bottom before being offloaded and removed for its next drive towards Hackney.