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The project is one of the largest in Europe. At £4²ú²Ô, its construction is a huge investment and a massive risk for BAA. However, as Peter Rogers, chairman of the strategic forum, notes in his foreword to this supplement: the cost of construction has been the single largest threat to BAA's survival.

The solution at Terminal 5 has been to revolutionise the construction process. For the past decade, BAA has been trying initiatives on other airport projects in preparation for the "big one".

It has also been developing relationships with its suppliers and consultants. Now many of these initiatives are being pulled together to ensure that the project is a success.

T5 has a five-year schedule, and 22 months and £1.1bn into the job, BAA's initiatives have started to pay off. All the construction milestones have been hit on all 16 of the major projects, and the whole thing is on schedule for its 30 March 2008 opening.

Fundamental to the success of this enterprise is the T5 agreement. A £4²ú²Ô project carries too great a liability for any construction team to bear, so BAA has taken it on and insured it. The idea is to relieve the project's consultants and contractors of what would have been a paralysing degree of risk, and thereby to free them to concentrate on managing it. If there is a problem, it is in the team members' interest to work together to find a solution (pages 34-36).

Each of the 16 projects has an integrated design and construction team, the members of which are expected to put the project first and their individual companies second. The agreement also means that, in addition to reimbursement for costs and an allowance for overheads and profit, the projects' suppliers are rewarded if they improve on budget and time targets and hit the project's milestones.

For the workforce, too, this project is different. T5 sets unprecedented standards for pay, welfare, safety and training. The project has already made national headlines with its offer to pay up to £55,000 for operatives if they hit all their targets. The reasons are pretty obvious: at its peak, the project needs 5000 skilled and committed workers at a time when such people are in short supply.

And having tempted workers to the site with money, BAA intends to keep them there by making it an attractive place to work. It is offering site conditions that are exceptional and workers' facilities that are second to none (pages 56-58). It has also invested heavily in inductions and training to ensure safety is not compromised; in partnership with the CITB, BAA has opened the UK's first on-site health and safety test centre. All workers have to pass the CSCS test within three months of starting on site.

The location of the project has forced BAA to do things differently when it came to organising the construction process. The site is in the middle of the world's busiest airport and hemmed in by some of Europe's busiest roads. There is nowhere to store materials. So an enormous effort has been put into just-in-time delivery and off-site prefabrication to keep on-site storage to a minimum, to improve quality and to limit the number of workers on site (pages 40-42).

As Peter Rogers says, Terminal 5 is a template for the future of UK construction.

What's been done so far …
Diverting the twin rivers
One of the critical project milestones has been the diversion of the site's two man-made rivers. The Duke of Northumberland's River and the Longford River used to flow across the T5 site. Not any more. To free up the ground, two channels have been constructed to divert the rivers around the western perimeter of the airport and to reconnect with their original route on the southern edge of the site. "Both rivers are now flowing in their new channels," says Phil Wilbraham, T5 landside's project leader.

The space around the perimeter was tight: the channels have been threaded through a narrow corridor between the A3044 dual carriageway and the airport's security fence. The channels have been constructed with concrete walls rising up from a clay and gravel bed. More than 8.5 km of river wall has been built. To save time, about 5 km was constructed from precast sections.

As part of the planning consent, BAA had to ensure that the river environment in the diversions was at least equivalent to the existing concrete channels. No problem: in the channels, BAA has placed hundreds of gabion baskets filled with gravel to force the river to meander from side to side. Placed on top of these are mats designed to anchor plant roots. Large branches and tree trunks have also been anchored to the river walls to provide habitat for river fauna.

Diverting the rivers into their new channels was a defined process to maintain the river ecology. Before the new channels were connected they were filled with river water from downstream and left for the sediment to settle and the clay riverbed to swell. Then, once everything had been pronounced satisfactory, the barriers were removed and the water from the old rivers flowed through the new channels. The existing rivers were drained slowly to allow fish to be caught and transferred to their new homes and to allow silt to be pumped from the beds of these rivers into the channels to kick-start their ecology. In early April, the team completed the process of taking out the fish and translocating silt from the old rivers to the new.

At the moment, the empty, original river channels still stand out above the site on a huge earth dyke, effectively splitting it in two. Currently, this dyke bisects the tunnels for the Heathrow Express, Piccadilly Line, baggage-handling and the passenger transit system. But not for much longer: archaeologists have just 10 weeks to investigate the site around these channels. "We handed over to the earthworks team on 14 May, three weeks ahead of schedule, on time and on budget," says Wilbraham. Come August, the earthworks team will finally have full access to remove the empty riverbeds, and the transport tunnels can be joined.

Making a stand fit for superjumbos
In a brief ceremony at 7am one morning in April, four aircraft stands were handed over to the airport operator. It was a significant event in the construction of T5, as they are the first parts of the terminal to be given to the airport operator.

For the taxiways and aircraft stands, Amec is using a new type of concrete to make them suitable for Airbus A380 "superjumbos".

If conventional aircraft-pavement-quality concrete had been used, the pavement slab would have had to have been 800 mm thick. However, using a high-flexural-strength concrete developed by Amec and TPS Consult, the slab has been kept to a thickness of 400-600 mm. This has led to a 25% reduction in the amount of concrete required for the pavements.

Before the concrete can be placed, the network of pipes, ducts and cables has to be installed. This will carry everything from power lines to aviation fuel. The lines are installed in precast concrete sections. The concrete is then placed over the top of these pits using a paving machine. It is surveyed, so that the concrete team can then saw through the concrete pavement to reach the duct access points.

The next set of stands is scheduled for handover in November; the remainder of the 47 stands will be rolled out as the contract progresses.