The Longest day

7am Rise and shine: Car park N5
It is seven o'clock on a dark winter morning in west London. Opposite the northern perimeter of Heathrow Airport, a stream of vehicles enter a desolate car park. Their headlights are dimmed under the street lamps' orange glow and the noise of their engines is drowned by the scream of aircraft landing nearby.

The drivers park their cars and join a group of men standing silently at a bus stop in the centre of car park N5. The bitter pre-dawn air steams their breath. Their shoulders are hunched, their hands thrust deep into the pockets of their high-visibility jackets. Occasionally, the headlights of a latecomer's car will flick across the gathering, illuminating the green T5 logos emblazoned on the men's jackets. These are some of the 5000-strong army of workers waiting to be ferried to the Terminal 5 construction site on this particular morning. Most are used to the gruelling commute, or will be by the end of the project: work on site began in November 2002 and is not due to finish until spring 2008.

The same routine is being enacted in all three of the huge car parks built close to the airport by BAA for the T5 construction workers. Eventually a silver "bendy" bus pulls up at the stop; the men swipe their security passes to enter. The bus will carry the men straight to the site. For them, another day's work on the UK's largest building site is about to begin.

The construction of the three car parks is just one part of the huge logistics operation BAA has put in place to get, at its peak, 5000 construction workers and 2000 support staff to site swiftly each morning. To ease demand on the buses, shifts have been staggered and some workers pitch up as early as 5.45am to avoid congestion.

"People are coming to work earlier and earlier to beat the traffic on the M25," says Dave Peacop, logistics production leader at BAA. In response, the firm is "developing the bussing operation to suit the changing arrivals pattern." It is not just the car parks that are served by BAA's fleet of 48 buses, which also pick up workers from Hatton Cross underground station – the nearest tube stop to the site and where BAA has built a depot for its fleet. A bus with the cryptic destination "Plot 9" ferries itinerant workers from Campsite Heathrow – the worker's caravan village to the west of the airport – to the main site. "We also put on buses to pick up pockets of workers from places like Cricklewood and Gravesend," says Peacop.

Once workers are on site, extra buses endlessly ferry people between the seven main site compounds, their workplace and the site entrance. "The site is one huge roundabout," explains Peacop. In addition to the 140-person-capacity "bendy" buses, BAA also operates a fleet of 4WD Land Rovers – dubbed "balloon catchers" – to take people to more remote workplaces.

8am On the move: Colnbrook logistics centre, 2 km from the airport
The first rays of winter sunshine reveal a huge, grey industrial shed fronted by a vast, flat storage yard peppered with empty lorry trailers and cylindrical orange tank containers, which transport pulverised fuel ash to the site. A goods train judders to a halt on the railway siding opposite the storage yard – this is the first concrete delivery of the day.

This centre is the key to Laing O'Rourke's logistics operation for T5. Along with another similar logistics centre south of the airport, it supplies materials to the construction teams building the concrete sub- and superstructures of the airport extension. The site's appetite for materials is colossal: 5000 tonnes of aggregate, 650 tonnes of Portland cement, 260 tonnes of PFA and 290 tonnes of steel reinforcement are consumed each day.

The railway siding is new. It was built to allow bulk materials to be delivered to the logistics centre by rail. "The roads around this site are some of the most congested in Europe," says Stuart Barr, demand fulfilment manager at Laing O'Rourke. Rather than add to the congestion, BAA arranged for the construction of the railhead. At Colnbrook, the rail-transported materials are switched to lorry for the short drive to site.

Despite the size of the T5 site – it is roughly the area of London's Hyde Park – there is nowhere to store materials. "There is limited lay-down space on site for materials – often we can only store enough for a day's use, or less sometimes," explains Barr. The challenge for him and his team is to ensure the right resource is delivered to the right place at the right time – every time.

The huge quantity of materials needed each day means the logistics centre also has the storage capacity for just one day's supply. Colnbrook operates on a just-in-time basis, with materials for the day's construction put in place on site the evening before. Materials for the next day's tasks are assembled and placed on lorry trailers at the logistics centre; they will be delivered to site later that day. For some critical materials, the logistics centre will hold a one-day buffer.

In the industrial shed, steel reinforcement is being pre-assembled for delivery to site. The prefabricated cages are then craned into place straight from the delivery vehicle – which cuts site work and eliminates the need for on-site storage. According to Barr, prefabrication of reinforcement has other advantages. "Factory production improves the quality of the assembly, the factory is a safer working environment and production is quicker in factory conditions, which improves workflow," he explains.

Stepping through the giant loading bay door into the glare of artificial light, the visitor is greeted by frantic activity and a barrage of noise. Groups of men tend to rows of clattering machines, which cut and bend the steel rods before disgorging them, noisily, on to racks. Nearby, other gangs are hard at work assembling the bent rods and bars into steel reinforcing cages and mats by wiring the rods to form a mesh.

Pre-planning is essential for the prefabrication to be successful. The "pull" from site controls the production of reinforcement and tells the logistics centre what is needed on a particular day. The logistics centre then tells the steel suppliers what it needs to take delivery of, and by when, to meet the site's needs.

A software package called Projectflow controls the production, and a production plan is drawn up with all stakeholders. Barr says this relies on trust. "The guys on site need to be honest about their requirements and need to have confidence that materials will arrive when they are needed," he explains.

If a job does not happen when it has been programmed, those involved are brought together to work out why, and what went wrong. However, the real bonus of this just-in-time prefabrication is productivity. "If we can increase the reliability of planned activities to 75% [currently the industry norm is 50%], then site productivity will increase by another 50%," says Barr.

9am two rivers run through it: the Western boundary of the airport
Work on the diversion of the two rivers that flow across the T5 construction site is critical to the whole project. "The twin rivers diversion is fundamental to the main construction programme," says Dave Palmer, T5 rivers team leader at drainage consultant Black & Veatch.

In their present location, the Duke of Northumberland's River and the Longford River flow south across the airport, each in a dedicated concrete channel. And because thousands of tonnes of earth have already been scraped from the site, lowering the ground level, the river channels rise above the site on a huge earth dike, effectively dividing the site in two and hindering construction.

To free up the construction site, two new river channels are being constructed alongside the western perimeter of the airport. Space here is tight: the channels have been threaded through a narrow corridor between the busy A3044 dual carriageway and the airport's security fence, a space currently occupied by the airport perimeter road.

The construction of the diversion is almost complete; two concrete walled river channels now encircle the western section of the airport like twin moats surrounding a castle. "We've had to take an existing road and turn it into two rivers and at the same time create a new road – all within 17 months," explains Palmer.

The channels have been constructed with concrete walls rising up from a clay and gravel riverbed. More than 8.5 km of river wall have been built. To save time and space, more than 5 km of wall was constructed from precast concrete sections (delivered from Colnbrook). Where precast wall sections could not be used, insitu concrete is used or in some cases sloping earth riverbanks.

The task now is to turn the two man-made channels into a more natural river environment. As part of the planning agreement, BAA must ensure the river environment in the diversions is equivalent to, or better than, the environment of the existing channels. To force the river to meander from side to side, hundreds of gabion baskets filled with gravel are being placed in sections on the riverbanks. Placed on top of these are what Palmer describes as "heavy-duty coconut doormats", which will anchor plant roots. Large branches and tree trunks are also being anchored to the river walls to provide a habitat for river fauna.

Once the "environment" is in place, the rivers can be diverted.

All that will then remain is to transfer some of the hundreds of tonnes of silt from the disused riverbeds to the bed of the new rivers. Only then can the twin rivers finally be demolished.

10am checkpoint t5: the Entrance plaza
Trucks loaded with construction materials roll in an unremitting convoy on to the Tarmac plateau in front of the single site entrance. A large security booth to the right of the gates gives the entrance the look of a jumped-up motorway toll rather than the entrance to a construction site. Vehicles leave the site through a second set of gates to the left of the security booth.

The comparison with a motorway is appropriate, given that this gate has to handle about 100 vehicles an hour arriving on site – or one truckload of construction materials every 36 seconds.

When security checks are complete and the drivers enter the site, the scale of its road system – complete with one-way systems, traffic lights and even speed cameras to enforce the 15 mph limit – becomes apparent. The overall effect is one of a congested and exceptionally muddy town centre.

10.15am helmers of the Deep: Earthworks team
Isolated mountains of earth and deep cavernous basement excavations are signs that the earthworks team have not been idle. "We've got 6.2 million cubic metres of earth to be excavated on this site – and so far we've shifted about 4.3 million," explains Keith Prince of Laing O'Rourke.

Material is excavated carefully. The site has a lot of naturally occurring gravel lying on top of London clay. Prince says the gravel is separated for use as backfill material before the clay is excavated.

The part of the site Prince is itching to let his excavators attack is the earth dike supporting the twin rivers – but for that he must be patient. In the meantime, to allow the basement of the main terminal to be excavated with the rivers still flowing, a huge sheet-pile wall has been constructed. "We've had to install a 100 m long, 20 m high sheet-pile wall to retain the rivers and stop them encroaching into the basement," says Prince. The wall towers above the 18 m deep basement. With the river diversion scheduled for completion in May, Prince will finally get the opportunity to demolish the twin rivers.

11am prefab sprouts: Substructures team
Deep in the shadow of the towering sheet-pile wall the concrete supporting columns for the main terminal building are under construction. On the flat expanse of the part-built ground slab, the substructures team are hard at work.

A tower crane lifts a dense rectangular cage of steel reinforcement from on top of the sheet-pile wall before swinging it into position. The cage is about the size of a small lift shaft; it was delivered prefabricated from Colnbrook Logistics Centre the previous evening. The crane lowers the pre-assembled cage into place on the column base and two men, working from the safety of a cherry-picker, unhook the cage from the crane. The reinforcing rods are then joined to those in the column base using pre-installed "couplers". Later in the day, men, again working from the cherry-picker, will install the column's shuttering, and that evening its concrete covering will be poured.

Colin Potts, T5 substructures production leader at Laing O'Rourke, is as evangelical as Barr about the advantage of prefabricated reinforcement. "Rather than taking a week to build a column base we can do it in six hours on site," he preaches. "We've moved from 20% pre-assembled reinforcement to 80%."

This is only possible because of the design process developed at T5. Every section of reinforcement is designed on a 3D computer modelling programme. According to Potts, the discipline needed to model the reinforcement successfully has been invaluable:

"It allows us to spot any clashes and it means we can check that gaps in information are obvious early in the design process. Eighty per cent of queries are raised and resolved during the modelling."

The finished reinforcement designs are then fed into the Projectflow software for the logistics team at Colnbrook to build. Reinforcement lead times are about five days, so if construction is to proceed smoothly, design information needs to be at Colnbrook in time for them to order the steel and fabricate the assembly.

Detail modelling of the reinforcement also allows the construction team to plan and sequence the construction while sitting in front of a computer screen. "The modelling programme is now used as part of our method statement," explains Potts. It also means crane movements can be planned and designers are able to work out the lifting points on an assembly.

12pm Burgers & chips: the site Canteen
It's noon, and the canteen at Compound B is doing a steady trade in lasagne, chips and burgers. The space has room for several hundred workers at one sitting. This is one of 16 "fixed" canteens on site; two mobile canteens service the remoter areas. In total, the canteens handle 22,000 transactions a week.

The operation is run by Eurest, the staff-feeding arm of the Compass Group.

Meal times reflect the operation of the site: tea and toast is served from 6 to 7am to cater for workers arriving early. Breakfast proper is at 10 am to coincide with the operatives' 30-minute mid-morning break.

Nouvelle cuisine this ain't: plates are heaped with energy-sustaining foods. "At the moment, because of the heavy labouring work on site, we're focusing on foods high in carbohydrates," explains Mark Lawrence, executive general manager at Eurest. The portions are enormous and £3.25 will buy you a substantial main course plus pudding and a drink. "We have to strike a balance between price, quantity and quality," says Lawrence. As the project progresses and manual labouring gives way to specialist fit-out teams and finishing trades, the carbohydrate content of the meals will be reduced.

Lawrence has tried some more adventurous fare, such as curries, but his customer survey highlighted the folly of this. He seems disappointed that his favourite food is not on the menu after it was pointed out that doing hard labour after a curry is not a pleasant experience.

The caterers are also responsible for running the site shop, which, in addition to selling snacks and newspapers, sells provisions for the hundreds of workers living in Campsite Heathrow. The shop even sells German newspapers after requests from the site's army of overseas workers.

12.45pm Medical matters: on-site Occupational health
Opposite the canteen is the medical centre. In the waiting room, three workers await treatment for minor ailments. Beyond the waiting room are the two treatment rooms. In one, a nurse is dressing a cut on a worker's hand. The room is packed with medical equipment – there's even an eye chart, weighing scales and an exercise bike. The room is so well equipped it would not look out of place in a general hospital. "We've got two rooms equipped to the standard of a minor accident unit," boasts Angie Young, occupational health manager at the medical centre.

The impression of the centre as a general hospital is given further credence by the four-wheel-drive ambulance parked outside. "We've had 50 call-outs so far, but there were only two where the London Ambulance Brigade were needed," says Young.

The medical centre is key to BAA's health and safety initiative. In addition to the treatment rooms, the centre houses a drug and alcohol screening room. In working on T5, operatives consent to random drug and alcohol checks by an independent tester.

Pre-employment medicals, for those in safety-critical roles, also take place at the medical centre. A safety-critical job could be a plant driver or crane operator, whose actions could jeopardise the safety of others. Young gives an example of an unfortunate applicant for a job as crane driver's post. "We found his eyesight was so bad he would have failed a driving test," she recalls.

In fact, of 1924 medicals carried out to May, in one-third of the cases the tests highlighted a problem such as raised blood pressure, diabetes or poor eyesight.

The medical centre also champions occupational health initiatives. Workers using tools that cause excessive amounts of vibration, which can lead to disabilities such as vibration white finger, are carefully monitored. "We've eliminated tools that have high levels of vibration from the site and we've time-tagged others to restrict use," Young says. She says the problem is that "manufacturers test tools under laboratory conditions" but under site conditions tools are often used in such a way that "safe daily exposure times are often much less than manufacturers' recommendations". Manufacturer Hilti is now working with the medical team to produce site-based usage times for its equipment.

The occupational health team also talks to the terminal's designers about minimising, or eliminating, occupational health risks. For example, the team is responsible for changing the design of the pile caps to eliminate the need to use hand tools to break out the tops of the concrete piles.

1pm Going underground: Tunnelling team
Back from lunch, the tunnelling team are already at work 20 m below ground at the foot of a 15 m diameter vertical shaft. Unlike the remainder of the workers on the T5 site, the tunnelling moles are dressed neck-to-toe in orange. Strapped around their orange waists are shiny metal boxes with emergency breathing apparatus.

The first 60 m of the Piccadilly Line extension tunnel has already been constructed. Peering down the concrete-lined hole, the rear of the tunnel-boring machine is just visible. The bore has been halted temporarily while the base of the vertical shaft is reconfigured to allow a narrow gauge railway to be assembled. This will deliver precast concrete sections to the boring machine.

After the noise and bustle of the main construction site, the peace of this subterranean workplace is disconcerting. The only sounds are the hum of high-voltage electrics and the clank of spanners as the men prepare the tunnel-boring machine for the next stage of the drive. In April, once the tunnel is complete, the machine will be used to bore the second Piccadilly Line tunnel. While the second bore is under way, the rail teams will install the track in the completed tunnel.

The project has nine tunnels, totalling more than 13.5 km. This includes two tunnels for the Heathrow Express, two underground lines for the Piccadilly Line spur and two road tunnels to link the new terminal to the remainder of the airport.

2pm prepare for Take-off: Airfield civil engineering
It is mid-afternoon at the eastern boundary of the site, the area closest to the working airport – not that you'd need to tell the team working here. Just the other side of a chainlink fence, a stone's throw away from the concreting team, is the main runway. Adjacent to this is a taxiway, where an endless line of aircrafts shuffle towards the runway. The stench of aviation fuel fills the air. Every 60 seconds or so the noise becomes excruciating as another aircraft thunders down the runway.

In the midst of this torment, a 300-strong concreting team is laying an airfield pavement to form aircraft stands and taxiways. When their contract finishes, Amec's team will have poured enough concrete to cover an area of 120 football pitches.

Later, the same team will be extending and widening the taxiways at the southern end of the site to make them suitable for the new A380 "super jumbo" aircraft. At 600 tonnes, it will weigh 200 tonnes more than the Boeing 747.

For the taxiways and aircraft stands at Terminal 5, Amec is using a new type of concrete. If conventional pavement quality concrete had been used to support the A380's enormous weight, the pavement slabs would have to have been 800 mm thick. However, using a high-flexural strength concrete developed by Amec, slabs have been kept to a thickness of 400-600 mm. "Although a cubic metre of this concrete is more expensive to produce than conventional pavement concrete, less of it is needed, which means it actually works out cheaper," says Peter Neal, airfield project leader at Laing O'Rourke.

Today, the concrete-laying plant sits idly at the edge of the site while workers cut service openings in the newly laid section of pavement to gain access to the fuel, water, low and high-voltage electric services installed before the slab was placed. The pavement here will form aircraft stands and the services will connect to aircraft while they are parked.

Under pressure from the airport, desperate for more stands to park aircraft, the handover of the pavement works is being phased. The first four stands are scheduled for handover in April this year, and handover of the remaining 43 stands will be rolled out as the contract progresses.

3pm Under one roof: the Main terminal building
Banks of floodlights flicker to life as darkness cloaks the site. Towards the western edge of the site, two enormous steel arches stand illuminated against the gloom; these are the first of the giant trusses that will span the roof of the main terminal building.

The roof is constructed independently of the terminal's internal structure. In a pool of light at one end of the trusses, a crane lowers rectangular sections of roof covering on to the giant steel purlins spanning the two arches; a team of riggers, perched high above the site, slot them into place. In all, more than 3000 pre-assembled cassettes will be used to cover the building's roof.

The roof is on the terminal's ground-floor slab before being raised to its final height. The main terminal is being built from south to north, so that while the roof is put up on the completed ground-floor slab in the south, the building's basement at the north end is still under construction. Currently, the two trusses are supported above the ground-floor slab on a row of giant steel columns. A third row of columns is in place ready to support a third truss currently being assembled.

Once four arches are complete, the abutment structures that support the roof truss will be erected. The team has already trial-assembled one abutment at steelwork contractor Severfield-Rowen's base near Thursk in North Yorkshire.

With all four trusses assembled, the entire construction will be clad in its covering of roofing cassettes and the complete 117 m long, 56 m section of roof will be jacked up to its final height. The lift will be in two stages: first the roof will be raised from its supporting columns by 150 mm to allow the tie that holds the arch in a curve to be tightened. Then strand-jacks will lift the entire roof section into position, where it will be supported on the abutments.

In all, five 56 m wide roof sections and one 18 m section will be lifted into place, working from the south of the building. Once the first two are in place, they will be stitched together with a row of purlins and the covering of roof cassettes added. After the roof is in position, a standing-seam weatherproof covering will be added.

The first roof section will be raised in February. If all goes well, the team hopes to have 40% of the roof complete by April. It is a critical target: "If the roof is delayed, the entire T5 programme will be delayed," says Andy Smith, BAA's project leader for the terminal building.

4.30pm not over yet: Construction co-ordination team
As the buses start to take workers home, the construction co-ordination team sits down to discuss the next day's activities. Their role is diverse; one minute it might involve ensuring people on different areas of the project talk to each other to avoid potential conflicts of interests, another time they will be talking to the community to keep them informed. They also need to keep the airport abreast of what is happening on the site.

John Harden, production co-ordinator for T5, describes his role as "a lot of enabling, a bit of enforcing and a bit of playing referee."

Currently, the team is looking at how the hundreds of fit-out contractors can be accommodated on site. "We're still working our way through discussions on that one," says Harden. One measure being assessed is the use of the logistics centres to consolidate deliveries coming on site.

As Harden points out, getting the organisation right is crucial: "People have played down the complexity of T5; they say £200m and £400m projects have been done before, but here we are doing 18 projects at once – and that requires a lot of co-ordination."