Construction has got off to a flying start at London Heathrow Airport’s new US$5.8bn Terminal 5 (T5), with work on the tunnels playing a major role. About 13.5km of bored tunnels and about 5km of cut and cover tunnels are currently in progress.
The first bore of the US$88.5M Airside Road Tunnel was completed in December 2002, after starting in June 2002 (see T&TI, July 2002, p28-31). Boring on the second tunnel got underway in February this year, and should be completed by June 2003.
The 8.1m i.d. tunnels are being constructed using a Herrenknecht dual mode TBM, capable of operating in either compressed air or EPB mode. As on all the bored tunnel contracts, the Morgan/Vinci JV is the contractor, with design carried out by Mott MacDonald.
Another major bored tunnel already underway is the 4.1km long, US$24M storm water outfall tunnel (SWOT), to the south-east of T5. A single 2.9m i.d. tunnel is being bored with a Lovat full-face TBM – it had achieved 160m by the start of April. The first 40m of the tunnel was constructed using sprayed concrete lining, oversized to provide an area for TBM assembly. From this point, the TBM will erect a precast concrete expanded wedgeblock segmental lining, which requires no annulus grouting.
Operating in clay, the TBM will run in open mode, with spoil removed from the cutterhead using a belt conveyor. The face can be closed completely using flood doors fitted to the cutterhead, to stabilise it during shutdowns.
Pipework installed in the tunnel will allow harvested rainfall to be used in the main terminal heating systems.
Two other major bored tunnels on the T5 project are the extensions to the Heathrow Express (HexEx) and London Underground‘s Piccadilly Line (PiccEx).
A 6.1m diameter Dosco open-face TBM, fitted with a roadheader boom, will construct 1.3km of the 1.7km long US$67M twin bore HexEx, starting in February 2004. The rest will be a reinforced concrete cut and cover box, which will also serve PiccEx. Lining on both bored extension sections will be precast expanded wedgeblock segments.
The US$54M PiccEx twin bore tunnel will be constructed using a 4.8m diameter open-face TBM, also fitted with a roadheader boom, starting in November 2003.
Other tunnels include two pipejack tunnel drives under the A3044 to bring electricity cables and water pipes onto the site. These will be constructed using a refurbished Herrenknecht backhoe open-face shield. Work is also underway on the cut and cover baggage, service and track transit system tunnels, constructed by Laing O’Rourke. All tunnels should be completed by February 2005.
