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Future of Tunnelling | Battersea Power Tunnel


Redevelopment of London’s Battersea Power Station has required intricate tunnelling to supply its inhabitants with electricity.

London’s Grade II listed Battersea Power Station stopped functioning in 1983 but, after many years of stalled attempts, it is now set to regenerate the local area as part of a vast new development.

Work beneath the ground to bring electricity to the new development and the surrounding Nine Elms development has required a major effort. A new substation connected that to the existing power grid is key. This connection involves construction of the 320m long Battersea Cable Tunnel. Including associated works, the power project is costing £42M.

“This project will deliver essential new electricity supplies that will breathe new life into a once-derelict part of London,” says Nirmal Kotecha, capital programme and procurement director for project client and co-funder UK Power Networks.

One of the biggest challenges on this project is that we’ve got to maintain security of supply

 The 320m long spur tunnel, dug using an open-face shield, is not in itself exceptional. What is, however, is how this is being linked in to the existing – and in use – 2.95m outside diameter wedge block tunnel that houses 132kV cables. The design and construction methodology also had to grapple with the additional complications that a densely built up area 20m above, 1.6m and 300mm diameter sewers 12m above and a live railway 10m away all threw the project’s way.

“One of the biggest challenges on this project is that we’ve got to maintain security of supply to our London customers across Battersea, Nine Elms and also to the north side of the river to central London,” says UK Power Networks project manager Rosemary Bridger.

Consultant Cowi, working alongside main contractor Clancy Docwra and tunnelling subcontractor Joseph Gallagher, came up with a unique hand excavated “junction chamber” as the solution. Essentially this is a carefully crafted 9m by 6m by 6m reinforced concrete cast insitu chamber 20m below ground that encases the new and old tunnels and forms the new connection between them. Naturally the logistical and engineering challenge so close to an existing power supply meant this was the riskiest part of the whole scheme and the sequence of work was vital.

A tunnel boring machine (TBM) drove the 2.44m internal diameter spur and stopped 4m away from, and perpendicular to, the existing tunnel. Site workers disassembled the TBM, leaving the shield insitu, and installed internal propping to support the wedge block tunnel and prevent deformation while the permanent works were completed. Extensive monitoring equipment, alerted the project team to movement during excavation and unloading.

The 11 week TBM drive through London Clay paved the way for work to begin on the junction chamber around mid-2017. Work on the concrete chamber finished late last year and the work to pull the nearly 50km of power cables into place is set for completion by April.

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