The vast industrial cathedral of St Pancras is testament to the ingenious engineering of our Victorian forebears and the endurance of wrought iron. But how can it be made into a 21st-century terminus?
In less than two years, St Pancras International will be the jewel in the crown of a new Continental journey. Two hours and fifteen minutes after leaving Paris, passengers will disembark at one of London’s most famous landmarks before continuing their journey into the metropolis. At last, the British part of the journey will equal the French – and arrival in London will be a more uplifting experience than detraining at the dingy Gard du Nord at the other end.
But creating this grand finale has been extremely complex. “No job I have ever done before has this mix,” says Ailie MacAdam, Bechtel’s contracts manager, who has the task of delivering the station. One minute she’s poring over the delicate refurbishment of the grade I-listed station, the next she is making heavyweight decisions about civil engineering. This unusual blend reflects the decrepit state of St Pancras and the need to not only refurbish it but to bring it up to modern standards. Furthermore, it has had to be extended to accommodate the 400 m long Eurostar trains. As if that weren’t enough, the project includes two new stations just outside St Pancras and a third one underground. Delivering this mix on budget and on time while keeping the neighbours and English Heritage happy has been “extremely challenging”.
An unexpected cemetery
An early hiccup in the project was the discovery of 7000 bodies. “That stopped us in our tracks,” says MacAdam. “We couldn’t do the piling for the north end of the east extension. What made it difficult is they weren’t in coffins – it was a mix of mud and bones. We got permission to move it all off site so they could be sorted out away from the critical path.” The bones delayed the project by three months. To MacAdam’s dismay this meant shifting a milestone – the completion of the east extension. “We had to re-sequence the rest of the job,” she says.
What made it difficult is they weren’t in coffins – it was a mix of mud and bones.
The next stage of the work was particularly critical because it meant severing the Thameslink connecting Bedford to Brighton. Once the east side of the extension was completed in April 2004 work could start on the west. But the new Thameslink station box had to be built first because it was to be constructed on the line of the existing Thameslink tunnel, and that happens to be directly underneath the west extension. Because the line had to be closed to build the Thameslink box, 24 hour working over 27 weeks was proposed.
Problems with the neighbours
Unfortunately for MacAdam and her team, the neighbours living in nearby flats complained. “Camden council refused the application for 24 hours working. We had to work out how we were going to deliver the job without working the hours.”
The team put their heads together. “This was a good example of how the project manager and contractor worked together to come up with ways of doing it,” MacAdam says. The answer was to modify the technique used to build the Thameslink box and to build the west extension deck simultaneously. Piles were sunk on either side of the Thameslink tunnel while trains continued running through. These were bridged using precast beams to form the roof of the Thameslink box. Immediately that was done, work could start on constructing the columns supporting the west extension. The line was closed and excavation equipment was lowered through access holes to chomp away at the tunnel and surrounding earth back to where the piles had been sunk. The work was done in 35 weeks without 24 hour working.
We had to work out how we were going to deliver the job without working the hours.
Refurbishing the Barlow shed
Meanwhile work was progressing on St Pancras station. This couldn’t have been more different from the challenge posed by the Thameslink box. St Pancras was completed in 1865 and is the work of engineer William Barlow. “This is not only a grade I-listed structure but it’s very high up the pecking order, not far off St Paul’s Cathedral,” says Arup’s Andy McNulty, the structural engineer for the station. “It is also the most difficult technical job I’ve ever been involved in. The structure has been there for 140 years and we have to justify it into the 22nd century.”
When the Barlow shed was completed, the span of its roof was the largest in the world. The roof is a series of parallel wrought-iron arches, tied together at platform level by wrought-iron beams. McNulty’s first concern was the amount of excavation taking place on the west side of the Barlow shed. “Because it is a tied arch you could envisage the west side falling into these excavations,” he says. Together with the contractor, he came up with a contingency plan in case the worst happened: a series of adjustable bars was attached parallel to the tie beams. If the arches started moving in the direction of the excavation, the idea was to slice through the tie beams and lengthen the bars to prevent damage, or even a catastrophic collapse.
The wrought-iron roof structure had to be checked carefully for corrosion. The arch consists of an upper and lower box section that funnel together at the sides of the building into one box section made from a series of wrought-iron plates riveted together. “If you get any leaks in the roof above you’ve got a perfect gutter to channel water down into the plated box section,” says McNulty. He says these plated boxes were full of rubble, which formed a wet mush. “Given the environment it was surprising there was any iron left.”
Temperature variations would cause it to expand and contract more than the structure below. This movement would put lateral loads on the cast iron columns, which may then snap like carrots.
All the box sections had to be checked for integrity. Amazingly “it was in surprisingly good condition, which is testament to the corrosion-resistant properties of wrought iron”, he says.
The final part of the restoration takes place below platform level, thanks to the Regent’s Canal. The platforms are 6 m higher than street level so the tracks into the station could clear the canal. The entire platform deck of the Barlow shed is supported on 866 cast iron columns – the space was originally used as a beer warehouse.
“When we had done all our analyses we couldn’t get the columns to conform to modern criteria,” says McNulty. Part of the problem was the reinforced concrete deck needed for the Eurostar trains. This sits on top of the original columns and beams but E on top of the original columns and beams but the problem is that temperature variations would cause it to expand and contract more than the structure below. This movement would put lateral loads on the cast iron columns, which may then snap like carrots. The answer is to take up this differential movement by placing elastomeric bearings between the new deck and the existing structure to provide independent movement.
The area under the platforms will become a passenger concourse serving the stations. Three large apertures have been cut into the platform above to funnel light down into this space. Providing the team continue keeping the project on track in 2007 this space will be the end of a journey for both the construction team and the Eurostar’s continental visitors.
Project Team
Client London & Continental Railways subsidiaries Union Railways (South) and Union Railways (North)
Designer and project manager Rail Link Engineering – a consortium of Bechtel, Arup, Systra and Halcrow
Principle contractors
Contract 103 (Civil Engineering Works on King’s Cross Railway Lands) Kier Construction/Edmund Nuttall
Contract 104 (Railway Staging and Interface Works) Mowlem Rail
Contract 105 (St Pancras Station) Costain, Laing O’Rourke, Bachy Soletanche, Emcor Rail (CORBER)
How to keep the trains running on time
St Pancras needed not only modernising but extending to accommodate the 18-carriage Eurostar trains. Three extra stations also have to be created, one is for fast Kent commuter trains using CTRL track; the second is for the Bedford to Brighton Thameslink service; and the third is for the Midland Mainline trains that used to operate out of St Pancras.
The solution to these problems was to extend the northern end of St Pancras.
The east side of the extension will also provide platforms for the Kent line and the west side will handle the Midlands line. A Thameslink station has been built under the western side of the extension where it is served by existing tunnels.
This task has been complicated by the need to keep the Midlands service running during the works. The team achieved this by building the eastern half of the extension first, so it could become a temporary home for Midland Mainline trains. That was completed in April 2004, freeing up St Pancras for refurbishment and modernisation. Work is under way on the west side of the extension, which has been built in tandem with the new underground box for the Thameslink station. When the extension is finished the Midland trains will move to the west side of the extension, and the Kent service will operate from the east side.
A bigger dig
Ailie MacAdam’s last big job was running part of the Big Dig, a £250m roads infrastructure contract in Boston. “When I was working on the Big Dig I thought I would never be involved in anything like it again – then I got this.” Now she is Bechtel’s contracts manager on St Pancras International but this title understates her role, which is project managing the whole job.
“What makes me tick is turning a station that was condemned into a state-of-the-art facility that will be used for another 150 years,” she says. “Knowing that is very motivating, despite all the problems along the way. The trick is to break the job down into manageable sections, which is the key to managing any big project. The thing with project management is to identify problems early so you can mitigate them.”
That said, it was inevitable on a project of this scale that unforeseen problems would crop up. “My worst day was when we found that the north gable of the Barlow shed was badly corroded, which meant it was going to take much longer to repair than programmed,” she says. “It was the first thing that made me think I would have to move one of our key milestone dates. In the end I found a way round it by working out a safe pedestrian route underneath so work could continue on the west extension.”
But the low points are balanced out by the highs. “Opening the interim station [for Midland Mainline] was great, as was the Thameslink box – making that milestone was terrific,” says MacAdam. But what will she do when this project is completed in 2007? “My husband wants to travel so it could be anywhere else in the world. We will have to see.”
I’ve never had a really bad day…
Paul Baldwin is the senior construction engineer with Arup and is responsible for administering the contract on behalf of the project manager – a sort of link between the project manager and the contractor. “There are a tremendous number of interfaces between the contractor and the specialist contractors on the Barlow Shed, I have to ensure all this runs smoothly.”
A good example is 21 chimneys that are adorning new buildings on the east side of the Barlow shed. These were constructed using bricks, mortars and stonework identical to the Victorian originals – the original buildings here were in such poor condition they had to be demolished. “In terms of modern construction it’s pretty much unique,” says Baldwin. “The bricklayers found it hard at first using lime mortar rather than cement-based mortar but once they had got through that they took great pride in what they were doing. When they are motivated like that it makes it much easier.”
Baldwin says there never has been a really bad day. “I am too much of an optimist,” he laughs. But there was one day that stands out in his memory, “That was the day the Olympics were announced, that gave an added impetus to the work,” he explains. “This project is connected directly to the Olympics at Stratford and the International Olympic Committee visited us to see the works. Winning the Olympics make it all seem more relevant and gave the site a real buzz.”
At the cutting edge
Boring the tunnels for CTRL was an important part of the project as there are 21.5 km of track in tunnels in section 2 – the bit that dips under the Thames near Ebbsfleet in two 2.5 km tunnels, surfaces then dips underground again at Dagenham for the final 19 km run into St Pancras International.
The CTRL tunnels are deep, in the wet sands below the stable London clay, which meant that high-tech Earth Pressure Balanced tunnel boring machines had to be used. “We could drive the tunnels through water without anything coming in,” says Gordon Battye, Rail Link Engineering’s senior tunnels engineer for the works. “The machine excavates the wet ground while supporting the cutting face.”
Eight boring machines were built for CTRL at a cost of £6m each. A revolving head spins around, cutting away at the ground; the spoil
is then carried away from the cutting head by an Archimedes screw and a conveyor belt. Foams and polymers are injected into the spoil to make sure it moves cleanly from the cutting head and through the screw.
The machine moves along in 1.5 m sections. Once it has cut away the spoil, 10 precast concrete sections are inserted to retain the tunnel wall. The machine then moves another 1.5 m. According to Battye the machine can cut and line 90 m a week.
The machines are guided using a computer system. A datum point is established at the beginning of the tunnel using GPS. As the boring progresses, the position of the machine is calibrated with the datum point using lasers. Battye says: “At breakthrough we were accurate to 11 mm.”
Right down the line
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