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Blackfriars Rail Bridge back in Business

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This article is being written on an auspicious day for Network Rail’s project at Blackfriars. Today, 5 December 2011, the new South entrance of Blackfriars station opened to the public for the first time, making the station the first new one on the South Bank in 125 years.

On 12 December the North or Common entrance was due to reopen as well, making Blackfriars the first station to bridge the Thames. At the same time, the first 12-car Thameslink trains will begin to operate through the station. The first fruits of this complex and challenging project will then really become apparent to travellers using the station and associated routes.

Lindsay Vamplew, Network Rail’s project director, and his team deserve hearty congratulations for getting this far, for they have been managing a demanding combination of challenges since work began in 2008/9. The project has involved, inter alia, a major river bridge, a main line rail station, a London Underground station, another underbridge over a busy thoroughfare, and the management of the realignment and upgrading of a busy railway layout and its signalling. All this has had to be managed whilst both railways remained operational most of the time and without disrupting traffic on the Thames below.

Planned works

Readers will be aware from earlier articles that the planned works involved the provision of four new platforms at Blackfriars and the dedication of two through lines to Thameslink. Plans also included the rerouting of those two lines to the opposite side of the station from before so as to avoid conflicting movements with the terminal lines. To achieve this, the river bridge has been repaired, strengthened and widened and the entire station has been rebuilt to occupy the whole bridge.

A new South entrance has been provided on the south bank of the Thames to complement the reconstructed North entrance on the opposite bank. The Thameslink lines are capable of handling 12 car trains and will be able to deal with 24 trains/hour in each direction once the remainder of the Thameslink route has been brought up to this capacity.

Early stages

An early stage in the project, completed at Christmas 2009, was the replacement of the rail bridge just south of Queen Victoria Street. A major job anywhere else, this meant the provision of a new 350 tonne composite structure with a 22 metre span to replace the original Victorian bridge.

In parallel with this, the Blackfriars underground station is also being refurbished and improved to cater for future demand and is expected to reopen in February 2012. The final two additional terminal platforms in the main line station are due to come into operation in May 2012, completing the project.

Double design

Such has been the complexity of it all that two design teams have been involved. Jacobs has provided the structural engineering input for the buildings works, whilst that for the bridgeworks has been provided by Tony Gee & Partners.

Steel fabrication has also been divided into two contracts, Watson Steel Structures being the main steelwork contractor and Bourne Steel providing the fabrications for the two new station entrances. Approximately 8,000 tonnes of steel has been used in the works in all. The main contractor for the whole scheme has been Balfour Beatty.

Rooted in the past

The site of the main line railway works has been a Victorian river bridge, and the whole of the site has its “heritage” literally underpinning everything. For example, when constructing foundations for the new underground station, the team encountered the remains of the original Victorian railway station.

This heritage has created some interesting conundrums. For a start it means that almost everything has to be measured and made individually for a specific place in the bridge or the structure of the new station. Standardisation was not a concept that seems to have been applied when the bridge was built over the Thames, and this has meant mirroring the variations of the bridge structure in the new works in many ways.

A key example of how this has affected things is given by the precast concrete units manufactured by Charcon for the construction of the new station platforms. No two units are exactly the same because of the variations in the geometry and dimensions inherent in the supporting bridge structure. Since the site is necessarily very confined, and because there were limits to the amount of weight that could be imposed upon the bridge, it was not possible to stockpile significant numbers of units anywhere on site.

Charcon therefore had to construct the units to exact individual dimensions and deliver them to site for installation in precisely the correct order, as required by main contractor Balfour Beatty. To facilitate this, Charcon set aside a dedicated area in their factory exclusively for this project. A special self-compacting concrete mix was adopted in order that the units quickly gained sufficient strength to be handled without damage. Transport to site was constrained by the bridge location too, and so, like most other materials, the concrete units had to be delivered by water. In this case, they were moved from Tilbury to site on barges operated by Bennett’s Barges (like Charcon, a subsidiary company of Aggregate Industries).

Complex project

Tony Westlake of Tony Gee & Partners reiterated the complexity of the project when I spoke to him. Whilst the partnership was engaged to carry out structural assessment and design work in relation to the strengthening and widening of the river bridge, Tony estimates that this probably accounted for only about half their work. The remainder of their efforts went into what he called “construction engineering”, including temporary works designs, the assessment of existing/re-engineered structures to ensure that they can carry the loads imposed during construction (such as the loadings from the crawler cranes employed on each bridge span) and the logistical issues of getting prefabricated steelwork and other large items into the site in good time. It included careful analysis of the processes of deconstruction and reconstruction required in repairing and widening the existing bridge structure. This brought back into use the nearer columns of the redundant bridge piers, which have stood in the river alongside the bridge for many years, as supports for the widening on that side of the structure.

As with the concrete platform units, and for the same reasons, the new steelwork was pre-assembled as far as possible off-site, this time at Thames Wharf, and again barges were used to bring materials to the site of work. The use of river transport had the additional benefit of avoiding many lorry loads travelling over London’s congested roads.

Keeping trains moving

Much effort went into deciding the right sequence for the prefabrication and erection to optimise the construction process. The need to keep trains running on both the National Rail and LUL lines throughout the project, with very few track possessions, required further care in the design and sequencing of the works. It was this that led to the decision to split the works into east and west halves, allowing the half not being worked on to carry the mainline rail services whilst the other side was dedicated to the project works. The eastern side was completed first, then the switch was made to the west, and in 2011 it has been this second half that has been the focus of work.

To help with this construction engineering process, the main contractor, Balfour Beatty, was appointed and brought into the project early, and assisted in the design process in order to increase the “buildability” and safety of the design.

Pride of place

The project team is particularly proud of three features of the job. Firstly, the 4,400 photovoltaic panels to be installed on the station roof will make the station the possessor of the largest solar array in London to date and the biggest solar bridge in the world. The panels, designed specially for the site and supplied by Sanyo, will generate 900,000kWh of electricity every year, and are expected to supply about half the annual energy requirement of the station. The panels were a challenge to design. They needed to be especially lightweight because of the project’s need to avoid over-stressing the river bridge, but at the same time, due to security requirements, they had to incorporate shatterproof materials.

Secondly, the “flying staircases” of the south entrance are quite spectacular. Cantilevering from the main structure between a mezzanine above street level and the platform level above, they apparently have fantastic views of the river and surrounding area.

Lastly, but certainly not least, the whole complex will be completely accessible for disabled travellers. Whilst this is the norm we expect of new projects, it is still relatively unusual for transport hubs in London. Network Rail and Transport for London will be delighted to see this site added to the list of upgraded locations that meet modern expectations in this way.

Chris Parker
Chris Parkerhttp://therailengineer.com

Conventional and slab-track, permanent way, earthworks and embankments, road-rail plant

Chris Parker has worked in the rail industry since 1972, beginning with British Rail in the civil engineering department in Birmingham and ending his full-time employment at Network Rail HQ in London in 2004. In between, he worked in various locations including Nottingham, Swindon, Derby and York.

His BR experience covered track and structures, design and maintenance, followed by a move into infrastructure management. During the rail privatisation process he was a project manager setting up the Midlands Zone of Railtrack, becoming Zone Civil Engineer before moving into Railtrack HQ in London.

Under Network Rail, he became Track Maintenance Engineer, representing his company and the UK at the UIC and CEN, dealing with international standards for track and interoperability, making full use of his spoken French skills.

Chris is active in the ICE and PWI. He started writing for Rail Engineer in 2006, and also writes for the PWI Journal and other organisations.


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