Crossing London by mainline rail is no easy task as no single central terminus exists to serve the railway passenger. Instead, London’s various mainline stations, which form a ring of satellites around the city’s central area, are connected by the London Underground, often crowded and subject to delay. Over the last century, numerous proposals for linking these termini have been suggested. However, it was not until 1987, when the Central London Rail Study was published, that a feasible solution was put forward.
The north-south (King’s Cross to Victoria), east-west (Liverpool Street to Paddington) mainline train link proposed in the report, commissioned by the Department for Transport, London Regional Transport, London Underground and British Rail, has since provided the basis for current ‘Crossrail’ plans.
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The case for Crossrail
Only three rail lines currently cross London: Thameslink, which runs north-south, connecting five London stations; the West London Line, which connects Watford in the north-east to Clapham Junction in the south; and the North London Line, which runs in a northerly arc from south-west to south east. Therefore the proposed additional Crossrail routes, designed to ease congestion and provide future growth, have received overwhelming support, particularly from London’s business community.
In 1991 a project team was established to develop, procure and manage the design of the central section of the Crossrail project. Parliamentary powers were sought for a 9km tunnelled route from Paddington to Liverpool Street, with intermediary stations at Bond Street, Tottenham Court Road and Farringdon.
In 1992 a Bill was subsequently put before the House of Commons and failed. The scheme was last shelved in 1996 following an economic recession, a reduction in passenger numbers, and an increasing lack of interest from the Government. However, the possibility of new tunnels crossing under London, carrying rolling stock that could connect directly to mainline services, has continued to excite the beleaguered London public, which is currently faced with either congested streets or a crumbling Underground network.
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By GlobalDataThe dustsheets were eventually pulled off Crossrail in 2001, when the Government instructed the Strategic Rail Authority (SRA) and Transport for London (TfL) to form a joint equity company, Cross London Rail Links Ltd (CLRL), to further develop the project. CLRL was given US$249M to reassess the central area designs, develop new route options, and prepare a business case that will go some way towards solving London’s transport problems.
Crossrail finally received the Government’s seal of approval on 14 July 2003, allowing CLRL to commence the public consultation process, undertake the environmental impact assessment and prepare a hybrid Bill, that could be presented to the House of Commons in November 2004.
Announcing the Government’s support for the project, transport secretary, Alistair Darling, said, “there is a clear transport case for Crossrail and we remain committed to the scheme”. An overwhelming majority of London’s residents, and most importantly the business community, support Darling’s sentiments.
Furthermore, they also support Darling’s intention that those who will directly benefit from the scheme, also pay for it. In an open letter to the Government, more than 50 business leaders and trade unionists said, “Not proceeding [with Crossrail] is a high-risk strategy for London and the UK”.
Cross London Rail Links
CLRL is charged with the task of developing route options and designs, and advancing the project through the hybrid Bill process. When T&TI recently visited CLRL’s offices, news of the Government’s decision was still eagerly awaited. However, CLRL’s tunnels design manager, Gordon Torp-Petersen, seconded from his role as a senior project design manager for Transport for London, was positive about the project’s future, “most people are 100% behind the scheme”. This assertion is backed up by reports suggesting London business leaders have already pledged up to US$3.2bn towards the building of Crossrail, as well as agreeing to the principle of a development tax that will help to pay for the project.
What is clear about the whole Crossrail operation, and the responsibility handed to CLRL, is the desire to get it right. “It is an enormous undertaking,” Torp-Petersen explains, “the work that we are currently looking at covers every aspect of what we are going to need to demonstrate to parliamentary scrutiny.” Faced with the prospect of handing a Bill to the House of Commons that demands US$16bn+ of private and public money, CLRL is understandably cautious.
“There is a vast amount of engineering going on, to ensure that all the ‘i’s are dotted and the ‘t’s are crossed. This will enable us to conclude at a point whereby, if we are then instructed to go forward, the engineering has all been worked out, and against that a full business case,” explains Torp-Petersen.
Route design
The 100+ engineers working on Crossrail in CLRL’s offices alone, are constantly value-engineering the design and refining the route to achieve the most efficient solution. There are two staggered projects: Crossrail Line 1 and Crossrail Line 2. Crossrail Line 2 is a scheme to link southwest London with northeast London, with a possible tunnel running between Victoria and Kings Cross, via Tottenham Court Road. This route will be addressed later.
The route that has just won the Government’s support is Crossrail Line 1, which includes the central tunnelled section between Paddington in the west to the Isle of Dogs in the east (see Figure 1). Ultimately, the line could link up with: Ebbsfleet International station, south-east of London; Shenfield in Essex, to the north; and Kingston and Heathrow, in the south-west. Some of these routes will include existing lines, while others will involve construction of new infrastructure, mostly tunnelling works.
However, it is the central section with a possible 17km tunnel that has caught the imagination of engineers, who appreciate the maze of existing tunnels and piles under the UK’s capital that could hinder a tunnel’s alignment. It is said that London’s geology is the most well-known in the world, but Torp-Petersen is not complacent. He is keen to incorporate as much knowledge gained on London projects, such as the Channel Tunnel Rail Link, and the Jubilee Line Extension, as possible. “We always learn. We would be very foolish if we didn’t,” he says. “We have a very comprehensive risk register, which has grown from the original risk register that Crossrail had in the 1990s.”
It was not a case of simply picking up where the project was left in 1996, nor was it a case of starting from scratch. Gordon Torp-Petersen and his team of engineers, including external consultants such as Mott MacDonald, have had to reassess every design. “Those were detailed designs,” Torp-Petersen explains.
“What we are doing at the moment is taking those designs, and seeing whether or not they need updating to meet the current standards.”
A case in point is the new Paddington Station. Like all the other designs on the Crossrail project, it has been viewed in terms of “constructability, versus time, versus money”, had input from local authorities, and incorporates new construction techniques. The result is a scheme, “which is a much better,” assures Torp-Petersen. “The old scheme was very good scheme, architecturally and engineering-wise. But in terms of programme, it was a little bit slower. What we’ve done is quickened it up. In terms of its cost, we’ve now got a more attractive scheme,” he says. After taking into consideration a number of constraints, such as the Grade 1 listed train shed, sewers, the Bakerloo Line alignment, and the continued use of the road above, the final Paddington Station design was a compromise between environmental impact and cost, resulting in a deep level diaphragm wall box, 25m deep x 325m long.
Physical constraints
Essentially, the Crossrail running tunnels follow a 6m i.d. (Figure 2) twin-tube design. The tunnels are bigger than the 3.8m i.d. London Underground tunnels, as they will carry standard UK rolling stock and be powered by both 3rd rail and overhead electrification in different sections of the scheme. Proposed construction is by eight TBMs on eight drives, launched in pairs from the eastern and western portals, and from an intermediate shaft near Liverpool Street. Two machines will also be launched from the Isle of Dogs station box. According to the preliminary construction schedule, the stations’ primary lining should be complete before TBMs arrive, so that they can be moved along the platform length before being relaunched on the next section.
Open-face machines will be used in the western part of the alignment, where the tunnels will be excavated through London Clay, and employ an expanded reinforced concrete lining. In the east, dual-mode EPBMs, with a gasketed reinforced concrete bolted lining, are likely to be used, where poorer ground conditions are expected.
The central alignment has been largely determined by physical constraints such as piled buildings and existing infrastructure, but it has still been possible to maintain the tunnels’ depth at between 20m and 30m, about the same depth as the Central Line. Although the client specification calls for a maximum speed of 100km/h through the central section, it is believed that this can only be achieved between Paddington and Bond Street, because of curvature restrictions. Horizontal curves have been designed with an absolute minimum radius of 300m, and a speed restriction of 80km/h. And while the desirable gradient is 1 in 40, it has been necessary to accept a 1 in 30 gradient in places, to avoid obstacles.
Over 150 boreholes along the tunnel alignment were drilled during the early 1990s, providing information on geological and hydrogeological conditions. Sampling, together with sophisticated field testing, was directed at obtaining the most reliable design parameters and ground stiffness models to assess ground movement.
The tunnels will lie predominantly in London Clay, but will fluctuate between London Clay, Lambeth Group and Thanet Sands out to the east.
The tunnel drives pass below many old, important, and protected surface structures. Principal settlement remedial measures most likely to be used are: curtain walling, compensation grouting, underpinning, structural jacking, and structural strengthening.
Two for the price of one
Stations along the central route will each cost an average US$325M. The basic design for the stations include a 240m long platform, to accommodate future twelve-car trains, and two ticket halls, one situated at either end. This, in effect, gives passengers two stations for the price of one. There is no standard method of construction for all of the stations, Crossrail, in this sense, does not employ the ‘one design fits all’ motif.
“Each station is slightly different in the way that will be tackled,” says Torp-Petersen. “Some will form a box construction, others adopt a sprayed concrete lining. If you take the principle of sprayed concrete lining, we will have intermediate construction shafts at either end, which will become ventilation shafts for the stations. We will use these as a means of going down and expanding along the platform. At Liverpool Street Station for example, there will be a shaft excavated as part of an emergency escape, that will go down inside Finsbury Circus. Excavation will be carried out from the shaft in both directions, to meet the excavations taking place from the Liverpool Street end, and from the box end at Moorgate, to meet the bored tunnels. So effectively one will have a four-pronged attack.”
CLRL has been asked to look at a number of different methods of procurement vis-á-vis the method of construction, but Torp-Petersen is not going to be drawn on unpublished designs. “We are looking at every single method that is currently on the market,” he says. “I cannot say at this moment that any particular method is being solely adopted. What we are looking at is the best method of construction to achieve the construction programme.”
It could be said that work has already started on Crossrail, with the construction of a brand new 26-storey office block at Moorgate Station. Underneath the building, a third of Crossrail’s ticket hall will be constructed, plus an 8m diameter, 35m deep draught relief shaft. “It was the subject of a 15-16 month negotiation,” says Torp-Petersen. “They have included the detailed detail designs from the 1990s into the building development, and our consultants worked with the developer’s consultants to come up with a combined scheme. When Crossrail goes ahead, it will not interfere with the building.”
The method of procurement will not be published until the Crossrail Bill is agreed by the Government. But this has not stopped speculation in the press, especially since Alistair Darling indicated that the private sector will have to burden a considerable share of the costs. Private Finance Initiative (PFI) is one method being discussed, along with bond options. “There’s wide and wild speculation outside, and I’ve been accosted a number of times and asked how this project is going to be funded, how it is going to be broken down. The problem we’ve got at the moment is that we are looking at every single option,’ Torp-Petersen says. “Is it going to be the same model as the Channel Tunnel Rail Link, where you have a single consortium. The final decision will come from the Secretary of State.”
Getting it right
Even with the Government’s backing, and the support of London businesses, the future of Crossrail is still very firmly on the drawing board. Not until the Bill is put to the House, will we have a full idea of what the project will entail. The Government has been criticised for having a lack of energy as far as Crossrail is concerned, aggravating many who look at other countries and see the comparative ease with which major projects get into the ground.
However, this must not detract from the diligence that engineers working under the CLRL umbrella have shown towards the scheme, and the determination to ‘get it right’. Every aspect of the project has been scrutinised, from design to implementation, meaning that if and when the project gets the green light, construction should be a success.
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