'Every metre of this route has issues, ' remarks RLE technical director Mike Glover, 'not because it was badly planned, but because people don't want you in their back gardens and so direct you to derelict or difficult land. There's always a reason why people haven't built there.' Nailing down the final shape of the route was a story of problem solving and negotiation with individuals, pressure groups, businesses, local and national government and parliamentary select committees.
Union Railways quality and environment director Ted Allett and environment manager Rachel Starling have been involved in the project since the early 1990s.
'At the earliest stage the route was going into Kings Cross, not St Pancras, ' says Allett.
'It took a southerly course, through some lovely countryside, entering London through Dulwich and Peckham.' Locals fercely objected. 'But [then environment secretary] Michael Heseltine promoted an easterly approach, developed by Arup in the 1980s, because of the perceived regeneration benet of passing through east London. That was it's raison d'etre, he argued.' Vast effort has gone into rening the route. Construction of a new station between King's Cross and St Pancras was brifley considered. But the focus rapidly shifted to re-use of St Pancras itself 'which was very run down and would have remained a sad old station without a huge injection of cash.
The station needed to be revived to kick start improvement in the surrounding area, ' says Allett.
Having broadly decided the alignment 'we had to micro navigate'. There were particular hot spots.
Kent County Council and the Highways Agency were anxious to avoid disruption to the A2/M2.
To pass beneath the road at sufcient depth, the new line was to be put into tunnel at Pepper Hill, passing beneath housing.
Residents were concerned about ground-borne noise, however, and pressed for the route to be moved further to the south, avoiding their homes altogether.
'We convinced the council and Highways Agency we could cross the A2 safely and without massive inconvenience, ' says Allett. 'We approached in cutting to gain depth and then crossed the A2 using cut and cover, doing it in slices. The key was undertaking to keep a minimum of three lanes open at all times.' Glover gets tremendously excited by the solution found to the next obstacles, Galley Hill Road and the North Kent Line.
The landscape has been pitted by chalk quarrying, with spines of chalk left to support local roads and rail lines. Such spines supporting the road and the North Kent Line presented walls in the path of the new line.
Taking possession of the road, 'at Galley Hill we worked from the spine itself, using it as a construction base. We installed foundations and abutments directly through it, then cast a deck, and finally pulled out the chalk spine material underneath to create a bridge, ' Glover says.
'But the piÞce de resistance south of the river was the way we went under the North Kent Line by performing an 8,000t bridge slide. We [RLE with joint venture contractor Hochtief/Norwest Holst] built the bridge, complete with spread foundations and abutments, off line, north of the railway. The whole thing was sitting on skid rails.
'We cut heading holes in the base of the chalk spine which enabled us to prepare the subfoundation and then pushed the whole thing into place during a 52-hour railway possession.
As we pushed, we were simultaneously ripping out the spine, and the whole bridge just slotted into the gap we'd made.
Crossing the Thames west of the QEII bridge was, at first glance, a highly attractive option.
The final alignment, taking the route east of the bridge, takes the line across the Wennington Marshes, part of which is a Royal Society for the Protection of Birds (RSPB) nature reserve.
'The westerly crossing appealed because it would have landed in a relatively industrialised area, dominated by scrap and salvage yards, ' says Starling. 'And it was drier.
It would have been a lot more straightforward.' But the alignment had a drawback, Starling reveals.
On the south of the Thames, 'we'd have had to go through old refuse sites with methane generation issues, and requiring us to become landfill site licence holders. We'd also have had to cut and cover across the M25 toll-booths. That was the nail in the coffin of that proposal.' An easterly crossing of the Thames enabled the high speed line to join the trace of the London Tilbury & Southend (LT&S) railway. An immersed tunnel sunk into the river bed was considered but the idea was killed by a number of nontechnical objections, in particular from the Port of London Authority, which was worried that a submerged tunnel in that location, on a bend, would be a navigation hazard.
This left bored tunnel as the only option. The length, depth and gradients of the tunnel were a balancing act between the desire to go as deep as possible to avoid fissures in the chalk and the need to clear the approaches to the M25 Dartford Crossing on the north bank of the Thames. 'We spotted that we could thread a viaduct between the Dartford Crossing and QEII Bridge viaducts, but had to come out of the ground at maximum gradient, ' says Allett.
Crossing in tunnel beneath the two structures was considered too risky and expensive.
The rail link continues across the waterlogged Wennington Marshes on a ground-hugging piled viaduct. Alignment was not the chief issue here; rather, on what kind of foundations the route should sit. Located within the flood plain the line had to be raised. A straight forward earth bund was not the solution, as land take in this ecologically sensitive area would have been too great. It would also have been prone to long-term settlement.
The resulting piled slab got the high speed line up to Dagenham, where it joined the paths of the existing LT&S line and North London Line.
Superficially, this should have made the going easy but, says Glover, 'the whole route is sandwiched between housing and over most of its length is in cutting of limited width. You couldn't have high speed trains running next to housing without serious measures to restrict noise.
'And then you'd have to have built your new tracks alongside an operating railway used by the North London Line freight trains.
In fact, you could only put in a new railway by taking out one of the existing lines. And there are huge logistical and safety issues if you are working next to a live railway.
existing railway as opposed to away from such constraints.
'Tunnels look like a big, heavy solution, but are very often highly economic.' Glover's assertion was put to the test as 17.5km of twin bore tunnels snaked beneath London Underground tunnels, cast iron water and gas mains, roads, bridges and hundreds of houses.
Diving into the ground at Ripple Lane, Dagenham, the line was to run in tunnel all the way to St Pancras, save for a brief glimpse of daylight at Stratford, where it passes through a mammoth box.
Glover explains by breaking the tunnel in two the emergency services could reach all parts of the tunnel within their maximum time limit, eliminating the need for a dedicated third bore for access and evacuation.
Emerging from tunnel at the London portal, just north of St Pancras, the line nally had to negotiate the spaghetti of existing roads and rail lines lying in the remaining 1km of its path.
York Way, a road built on viaduct running obliquely across the CTRL's path, posed a particular obstacle. 'The line goes over the East Coast Main Line and York Way, and then on into St Pancras, ' says Allett. This dictated the depth of tunnelling a couple of hundred metres back from the portal, where the CTRL passes under the busy Caledonian Road. 'Getting over York Way dictated cut and cover tunnel construction to get across Caledonian Road. You couldn't lower the tunnel under Caledonian Road to sufcient depth to use a tunnel boring machine and still clear York Way.' But traders on Caledonian Road were deeply unhappy, Allett says. 'They were worried disruption to the road would interfere with business. We tried to show that we could cut and cover tunnel while retaining one lane of trafc north and one south. But the parliamentary select committee insisted we nd another way of going under the road.' Stumped, the design team called for a fresh pair of eyes, drafting in an engineer who had previously worked in Kent.
'Almost straight away he said: 'Take away the constraint - take York Way off its viaduct'. It was a Eureka moment, ' Allett recalls.
By putting York Way at grade and realigning it, it became possible to drop the height of the CTRL viaduct crossing it.
This pulled the whole vertical alignment of the line and tunnels down a few critical metres, enabling the London tunnels to be driven along their whole length.
Allett adds that the solution suited the needs of the wider area. 'A highway on viaduct doesn't do much to encourage regeneration. You can't easily gain access to the land either side of it. By putting York Way at ground level you can build turnings off it into the King's Cross Central regeneration area.' The approaches to St Pancras International station are an essay in geometry, with sweeping radii and huge viaducts giving Eurostar and high speed domestic trains access to the international terminus and also to the three other lines radiating from King's Cross and St Pancras itself.
The CTRL leaps the East Coast Main Line (ECML) and runs neck and neck with the North London Line (NLL). In future Eurostars could join the ECML, NLL, Midland Main Line and West Coast Main Line, giving access to the rest of the UK.
Environment Construction of the high speed line got consent during the era that eco-warrior Swampy was making headlines. He famously tunnelled badger set-like labyrinths under the alignment of the A30 at Fairmile, Devon, and later in the path of Manchester Airport's second runway.
'Along the length of the high speed line we have congested areas of habitation, but also very ecologically rich areas of wetland and ancient woodland, ' says Allett. 'You'd have hit sensitive habitats whatever route you took.' 'Because we'd been through a very robust consultation before gaining Parliamentary approval, people realised that what we were doing was very well considered. They may not have liked it, but we got potential opponents on board, ' adds Union Railways environment manager Rachel Starling.
Prior to gaining consent the project team prepared what was reckoned at the time to be one of the most thorough environmental statements ever produced in the UK. During the two year Parliamentary Bill process half of all petitions were to do with the environment, Starling continues.
This led the team to make more than 600 commitments to various interest groups.
As well as trying to minimise the scheme's environmental impact, the project has committed to compensating for unavoidable damage.