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Medley of Tunnel Techniques Take Transit to Heathrow
By Peter Reina
New terminal will have transit links.

Stretching nearly 400 meters, the new glass-walled Terminal Five is the most visible element of London Heathrow Airport’s $8.3-billion expansion. But nearly a fifth of Terminal Five’s investment is hidden in over 13 km of tunnels, bored by four closed and open-faced machines.

Within weeks, owner BAA plc will begin commissioning a $1.2-billion project to extend two rail systems—London’s Piccadilly Line and its own Heathrow Express—into T5. By September, both will serve a new station under the terminal. T5 will open in a year to handle up to 30 million passengers annually.

Both London rail-link extensions to T5, located on a 260-hectare plot between two runways, are in twin tunnels totaling over 6.5 km. Tunneling also includes two bores of a 1.3-km airside highway and a 4.1-km-long storm drain. Underground work was “very successful in a very, very sensitive environment…when you consider the consequences of settlement,” says Ian Fugeman, BAA’s head of rail tunnels.

Located entirely in good clay, the Heathrow Express 5.7-m-diameter tunnels and the Piccadilly 4.5-m-diameter tunnels were driven by open-face TBMs. Another open facer dug the 2.9-m-diameter drain while a 9.1-m-diameter earth pressure balancing TBM drove the shallow road bore, partly through sands and gravels.

Tunnels. Good clay facilitated extensive tunneling work for Heathrow Airport expansion.

Underground techniques also included extensive cut-and-cover sections and the “observational method” for road tunnel portals. “It’s not really the [New Austrian Tunnelling Method],” says Arthur Darby, project director with Mott MacDonald Group, London, BAA’s lead tunnel design firm. Safety rules are so conservative that “you design for the maximum conceivable load,” he explains.

In some complicated locations, the contractor used a NATM variant without mesh or arches. Lasers set the cutting profile for the roadheader operator, while the face was excavated with a slight forward incline. “It’s a very safe system and very much more efficient and cost-effective than traditional methods,” says Selby Thacker, project director with Morgan Est Ltd.

Morgan Est teamed up with Paris-based Vinci Construction Grand Projets for T5. Both firms were selected individually a decade ago for the project. They were then encouraged by BAA to joint venture. “It was the biggest project that Morgan Est had undertaken and Vinci had not worked in this country,” says Thacker.

T5’s construction relies on hiring firms via long-term framework agreements that cover types of activity rather than using specific contracts. All parties work collaboratively while BAA takes on most of the risk and guarantees contractors’ profits. “From the very beginning, we realized we would not achieve our objectives…unless we went about procurement in a very different way,” says Fugeman.

With T5 claimed to be on schedule and budget, BAA is extending its procurement strategy and is recruiting the next wave of contractors. Some will design and build Heathrow’s next big project, the estimated $3-billion East Terminal, due to replace Terminals One and Two in 2012.


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