We tell the story of how the Channel Tunnel Rail Link is arriving at St Pancras
Step 1

2001-2002 Clear site ready for construction
The difficult part was not dismantling and storing the listed gasholders or diverting the 900 mm diameter gas main. It wasn't relocating the aggregate and cement businesses or building the depot for Camden council. It wasn't even threading the new high speed lines through the rat's nest of rails, restoring King's Cross' famous brick viaduct, taking up the busy roads that circle St Pancras and relaying them in a different position. And it was nothing to do with exhuming 7000 the corpses that they discovered. What made the project really challenging was doing all of the above while keeping the Midland Mainline service running. That required an incredibly intricate phasing system for the works. So complex, indeed, that that CTRL give its suppliers six months to work out how to do it, and how they would co-ordinate their roles.

Step 2

2003-2004 Build eastern half of new extension to St Pancras station
Critical to the phasing of the works was the construction of the eastern half of the St Pancras extension. This is a steel-and-glass rectangular box that will extend the Victorian station north and give it the platform-space to accommodate the enormous length of the 18-carriage Eurostar trains. In addition to sheltering the Eurostars, the extension will serve as the terminus for Midland Mainline trains and for a domestic service for Kent commuters, which is to use the Eurostar's tracks.

To allow the Midland Mainline to continue using the station, the construction of the extension has had to be phased. The extension is being built in two halves, eastern first; this will form a temporary terminus until the railway's permanent home, on the western side of the extension, is constructed later.

The present concern of the site team is to complete the construction of this part of the extension. The scene is one of mud, men and machinery as the construction team rush to meet the extension's April handover. Already, the structure towers above the site and its enormous saw-tooth roof is rapidly nearing completion.

Once the roofing team has finished installing the station canopy, work can start on the platforms. "The trick is to get the underside of the canopy finished, then get rid of the scaffolding so we can start work laying the terrazzo to get the platforms done," says construction manager. Mike Robinson. A track-laying gang is busy installing the lines that, in six months, will carry the Midland Mainline trains to their temporary shelter.

The level of activity is intense in the critical area beyond the canopy as the team scramble to pull back a delay of three months caused by the discovery of 7000 bodies, buried in the old St Pancras graveyard slap-bang in the middle of the area where the track laying team were to begin their work. The number of bodies uncovered was far more than had been expected and digging them up took far longer than had been anticipated. "It has compressed the programme," Robinson admits. "The push now is to get everything finished and ready for the track layers to start on the 12 November."

So far, work on the remodelling of St Pancras itself is confined to the outside of the station, where some of the buildings lining its flanks have been demolished. Inside, the only work to have taken place so far is the removal of the overhead power lines.

Step 3

2004-2005 Build new Thameslink station and start refurbishment of St Pancras
While the focus of attention at the north of the station is on getting the project back on programme, to the west of the station another team is working on the construction of a Thameslink station. This will replace the existing station, which is located some distance from the site. The station is being constructed below ground in the area that will be occupied by the western half of the St Pancras extension 鈥� so it is essential its construction be completed on time.

Currently, the Fleet sewer runs through the area where the station is to be constructed. This sewer is in the process of being diverted. The roof of the enormous, 2 m diameter, brick-built Victorian conduit is visible from a huge hole dug to accommodate the diversion. "Eventually it will pass over the top of the finished station box," says Robinson.

Constructing the station box itself is an enormous task. First, two parallel rows of piles will be sunk, one either side of the two existing Thameslink tunnels. More than 1000 piles will be used to form the sides of a roughly 600 m long box. Each row is capped by a huge concrete beam before the whole assembly is finished with a roof formed from concrete slabs.

In September 2004, after the contractor has taken possession of line, excavating equipment will be lowered through gaps left in the concrete roof. Their task is to empty the concrete chamber of earth to create the station box. The team have just six months to do this. To ensure the station is built on time, the piling contractor is pressing ahead sinking piles and casting capping beams. "We're doing preparatory work ready for the six-month possession," Robinson says.

Once trains start to arrive at the extension, the existing rail lines can be removed, the Victorian viaduct demolished, and refurbishment of the St Pancras train shed can begin.

Step 4

2005-2006 Complete redevelopment of St Pancras and build western half of station extension
By this stage in the project, work on the refurbishment of St Pancras station itself should be well under way. There is a huge amount of work needed to transform the station (see pages 44-45) and so, even though the contractor does not yet have access to work on its interior, it has commenced operations outside the building and in a massive undercroft beneath the platforms, which is to become a passenger concourse complete with ticket offices and destination boards.

Where possible, the team is attempting to get ahead, so some of this stage is being pushed through already. The jumble of sheds and lean-tos that used to line the listed building's flanks have disappeared, along with the lower part of the station's roof. In the undercroft, rows of naked bulbs reveal the extent of work so far: the original floor has been broken up and removed and with the slab gone, the ground has been excavated by about 1500 mm, exposing the base of the 818 columns supporting the platforms above. This excavation will allow a "Roman floor" to be constructed later in the programme as part of the undercroft's ventilation system.

With the Thameslink station programmed to be complete by this stage in the project, construction of the western half of the new extension should be in full swing.

Step 5

2006 Open western half of new extension and close eastern half
This is the final stage of the project. Once the western half of the station extension has been constructed, the Midland Mainline can move to its permanent home.

The contractor will then close the eastern side of the station extension, which was completed earlier in the programme, to finish the fit-out of its interior.

Step 6

2006 Open station
This part isn't that difficult.

How the project team is organised

London & Continental Railways (LCR)
Owners of CTRL and Eurostar

Union Railways (North)
Responsible for the provision of the Southfleet to St Pancras section of line

Union Railways (South)
Responsible for the provision of Channel Tunnel to Fawkham Junction section of the line

Rail Link Engineering
(A consortium made up of the engineering shareholders in LCR 鈥� Bechtel, Arup, Halcrow and Systra) Responsible for the line鈥檚 design, procurement, management and construction

Network Rail
Will maintain and operate CTRL under contract

Iron, steel, glass and beer: How a treasured Victorian steam-train station is being turned into a 21st-century terminus for high-speed intercontinental shuttles

St Pancras is an engineering and architectural gem. It was designed by William Barlow for the Midland Railway Company; at the time it of its construction in 1865, the station鈥檚 huge vaulted roof was the largest span in the world. 鈥淚t is an amazing high-tech structure, built 10 years before Eiffel Tower,鈥� says Alastair Lansley, Rail Link Engineering鈥檚 lead architect and the man responsible for transforming this grade I-listed masterpiece into a 拢450m station for high-speed intercontinental trains. Aside from its record-breaking roof, the station is unusual in that the platforms and train deck have been constructed 6 m above street level. This is because the railway lines had to be raised above the Regent鈥檚 Canal. Barlow used the platform鈥檚 elevation to his advantage; he created a huge undercroft beneath the train deck for use as a bonded warehouse to store beer transported to London from Burton-on-Trent. The undercroft is filled by a forest of cast iron columns 鈥� 866 in total 鈥� to transfer the weight of the train deck.

The columns are spaced 4.512 m apart, derived from multiples of a beer cask width. Lansley says the structure is so 鈥済utsy鈥� that it allowed the Midland Railway to move platforms around.

Lansley鈥檚 design exploits this undercroft. 鈥淚t provides a huge floorplate asset,鈥� he says. Instead of beer, the space will be transformed into a ground-level passenger space containing a ticket hall, concourses and arrival and departure areas. And there will be a pedestrian plaza with links to transport connections including King鈥檚 Cross and the Thameslink line will allow passengers to move between routes and the undercroft with ease.

To introduce daylight into subterranea, a series of rectangular holes will be punched through the station floor to the west of the Eurostar platforms. 鈥淲e鈥檒l use tin-snips to open up this huge volume,鈥� Lansley says. A reinforced concrete collar around each of the openings will ensure the original structure remains intact. 鈥淭he openings will visually link the train shed and undercroft volumes,鈥� says Lansley. Despite the building鈥檚 slightly-more-important-than-St-Paul鈥檚-Cathedral status, English Heritage have been co-operative. Lansley is full of praise: 鈥淓H has shown remarkable courage in accepting Rail Link鈥檚 proposals.鈥�

An international entrance will be created in the middle of the east wall where four of the arched windows will be sympathetically remodelled to create a grand entrance for intercontinental passengers. To give the entrance a presence, two 鈥渕onumental鈥� timber doors will be installed in the outer two arches. It will be 鈥淚ncredibly grand鈥� says Lansley. Above the entrance, a slender glass canopy will cantilever out over the pavement to provide shelter without detracting from the facade. 鈥淲e have to make it look as if Barlow had done it 鈥� we are playing God,鈥� explains Lansley.

The roof of the station will be returned to its original form. 鈥淲e managed to find every one of Barlow鈥檚 drawings in Kew Records Office,鈥� says Lansley. The drawings revealed that repairs to the roof after bomb damage during the Second World War were not true to the original. A solid roof had replaced a magnificent glazed arch. Lansley鈥檚 scheme will reinstate the 鈥渞idge and furrow glazing鈥� and the station鈥檚 glazed end screens will be reglazed to increase the natural light.

And, once the station鈥檚 roof has become a pristine version of the original, it will be kept in mint condition by only allowing Eurostar trains, which use electric power, to use the station. The Midland Mainline鈥檚 smoky diesels will be kept out.

Lansley鈥檚 design, which 鈥� for a glazed rectangular box 鈥� provides a deliberate contrast between the grand old station and its new extension. 鈥淯nlike the sinuous line at Waterloo International, this is dead straight and long,鈥� Lansley says. 鈥淚t is a simple space, levitated out of the back of the station 鈥� like a flying carpet.鈥�

Lansley鈥檚 design has a saw-tooth roof with northlight glazing, and perpendicular glazed walls. The roof is supported on a simple column and beam structure, which should minimise the its impact on the glazed box. The roof canopy overhangs the walls by several metres to shelter a opening at the top of the walls designed to vent diesel fumes and brake-dust. The lower section of wall is glazed to allow passengers to look out and public to look in to see the trains.

A rectangular glazed transept forms the junction between Barlow鈥檚 shed and Lansley鈥檚 extension. This transparent junction is a key circulation space to move passengers between the lower concourse and the elevated platforms. 鈥淚t is an old architectural clich茅 that the best way to join something is to separate it,鈥� says Lansley.

Construction team

For the works around St Pancras, CTRL project managers, Rail Link Engineering, combined two of the main contracts by awarding them to a single Costain鈥揙鈥橰ourke鈥揃achy Soletanche鈥揈mcor Drake & Scull joint venture to eliminate potentially problematic interfaces between two main contracts and to help to keep costs in check.

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