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First shaft finished for Thames gas main tunnel

National Grid Tunnel

Engineers have finished the first stage of a tunnel for a gas main under the River Thames, National Grid Gas Distribution’s biggest current civil engineering project.

The 330m long, 1.8m wide tunnel is being delivered by tRIIO, a JV owned by Morrison Utility Services and Skanska in partnership with National Grid Gas Distribution. The tunnel forms part of a £1bn project to upgrade London’s 2,897km of metal gas mains, although it is the only new one being built for the project.

Work has finished on a 30m deep, 7.5m diameter shaft at Royal Hospital Chelsea. The site had to be quickly cleared and the shaft covered with a concrete slab and topsoil to avoid clashing with the Chelsea Flower Show.

“I’m delighted to say that we’re proceeding according to schedule thanks to the hard work and commitment of our project team,” said project manager Andrew Hejdner.

A second 30m shaft with a diameter of 6m will be dug at the second site in Battersea Park, where work is underway to ready the site. Construction on the second shaft is expected to finish in August.

Once the two shafts have been built, a micro tunnel boring machine (TBM) will be lowered into the shaft at Royal Hospital Chelsea site. An operator at the surface will guide the TBM using remote control as it digs the tunnel, lining it with concrete segments as it goes.

After the tunnel has been dug a new gas pipe will be installed, bringing the project to a close in 2018.


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