Three cable tunnels in London with a combined length of almost 30km are out for tender by National Grid, which has set submissions deadlines of early September.
National Grid is preparing the tender stage for a fourth 4m i.d. tunnel, but the schedule for issue of documents and submissions has yet to be fixed.
The longest tunnel amongst those out to tender is the Hackney to Willesden route, which is 22km long and will have nine permanent shafts and three temporary shafts.
The tunnel is split into two sections: Hackney to St John’s Wood; Willesden to St John’s Wood.
The entire tunnel between Hackney and Willesden is to be built over 2009-15. Geology along the alignment comprises mostly clay. The tunnel was designed by Donaldson Associates Ltd.
The shortest of the tunnels out to bid, at 7.1km long, is the Hurst to Eltham section, which will have three shafts. The tunnel is to be built over 2009-2014 and has been designed by PB Power. Excavation will be mostly through chalk.
The fourth tender that is to be called shortly will be for the Wimbledon to Kensal Green tunnel, which will be 12.4km long and have five shafts. At Kensal Green, the tunnel links with the Willesden to St John’s Wood section of cable tunnel.
The construction programme calls for the Wimbledon to Kensal Green tunnel to be built over 2009-2016. Geology along the alignment is comprised mostly of clay. The designer is Mott MacDonald.
All tunnels four tunnels, with a total length of 41.5km, have been sized to provide space to lay additional 400kV cables in future, said the client. They will be excavated at depths of 12m-60m.
National Grid said the total investment in the four tunnels is approximately £600M (US$1.2bn).
Further ahead, it is considering construction of a 10.7km long cable tunnel from Eltham to New Cross.
National Grid has a number of cable tunnels in London out to tender
