The London Terminals: Blackfriars
“It’s probably fair to say that it’s not been easy. Everything fits in only one place, and almost everything had to happen at a very specific time. Frankly, this station was some kind of infernal jigsaw.”
– Rob Lines, Project Manager for Network Rail
Last weekend saw work at Blackfriars station reach a significant milestone, with the end of weekend and evening blockades and the opening of the new bay platforms. In addition to the return of various FCC services at night and at the weekend, this also meant that the new Southeastern service to Sevenoaks could begin, and the new FCC service to Sutton can start next Sunday. From a passenger perspective this will effectively mark the completion of the Blackfriars rebuild project, although some repair and finishing work on the bridge will still take place post-Olympics. In essence, this means that one of the most complex terminal rebuilds in London has now finally come to a close.
Whilst the impressive work at Kings Cross to the north has attracted a great deal of attention in recent months, it is arguably Blackfriars that represents the greater engineering achievement. Over the last three years the station has essentially been completely reworked, impressive given the station’s restricted site on the north bank of the Thames and the need to maintain as full a service as possible through the station at all times. Indeed in some ways the restrictions brought about by Blackfriars location have been turned into advantages – the new station spans the Thames, becoming the first London station to do so, and adds a new exit on the south bank that is already being used by almost one third of all passengers to the station.
As this article will show, however, bringing this new station into being has not been a simple exercise.
Originally opened as St Pauls in 1886, the station took its name from the railway bridge itself – St Pauls Railway Bridge, a wrought iron bridge designed by Henry Marc Brunel (son of Isambard) and Sir John Wolfe-Barry (more famous for a certain bascule bridge further downstream). The station saw the London, Chatham & Dover move its terminal to the north bank of the Thames. Services had originally terminated just south at Blackfriars Bridge, which became goods-only when St Pauls opened.
The rationalisation of the railways after WW1 and the creation of Southern meant that Blackfriars (as it was finally renamed in 1937) gradually became more of a suburban terminal, as intercity services began to be increasingly consolidated into Waterloo. This shift in focus, combined with the gradual deterioration of the infrastructure, led to Blackfriars being extensively rebuilt in the 1970s. This was followed, in the 1980s, by the demolition of St Pauls Railway Bridge itself and the complete shift of traffic to the current Blackfriars Railways Bridge immediately to the east. This moved the focus of the railway slightly eastwards, with the supporting piers and the southern abutment of the original St Pauls bridge left in place. The abutment was Grade II listed, but the piers were retained largely because removing them from the Thames would have been a costly exercise.
Expanding the Bridge
In order to fully understand the work that has taken place on Blackfriars as part of the Thameslink Programme, it’s important to understand the infrastructure legacy of all the above. Blackfriars had limited space for expansion to the north and one bridge, but – as much through luck as judgement – also an entire set of “spare” piers. Thameslink needed a reworked layout and longer platforms. The decision was made, therefore, to use the old St Pauls piers to widen the bridge and expand the station southwards out over the Thames. As an additional benefit, this would allow a southern entrance to be constructed, giving passengers a direct exit onto the southern side of the river for the first time.
The image above gives a good idea as to the general change in both track and platform layout that the rebuild has brought about on the bridge itself. What it doesn’t necessarily convey, however, is the complexity involved in putting this into place. The need to maintain a running (if not fully served) railway throughout the process meant that closing the bridge entirely during the rebuild wasn’t possible. As a result the work had to take place in stages, with the eastern half of the bridge redeveloped first whilst rail traffic continued to run on the west.
In order to accommodate the new platforms without changing the track layout too much, the bridge also still needed to be widened to the east, even if it was not as much as to the west. With no handily placed spare piers on the eastern side of the bridge, the decision was made instead to remodel the existing eastern piers to support the additional structure. Concrete shoes were thus cast and added to the bases, upon which the additional ribs required to support the platforms were then placed. The ribs themselves needed to be individually engineered, as each spandrel at Blackfriars is unique.
The above exercise may sound relatively straightforward. Look closer at the photos of the process above, however, and you’ll see hints as to why Blackfriars was an incredibly complex project – all this work took place above the Thames – a working, and importantly tidal river.
The impact that the Thames had on the nature, and complexity, of the work undertaken is difficult to underestimate. Beyond the obvious difficulties that come from working over major river traffic, the tidal nature of the Thames made heavy lifting difficult, as it could not be performed from the bridge deck. Lifting required the use of barges as lifting platforms – a process tricky enough without the ebb and flow of the river’s tide.
Indeed the tide also meant the need for some lateral thinking in relation to other elements of the work on the eastern side. In order to expand the piers, the existing facings needed to be removed. These extended below the high tide point though, and so simply surrounding them with a scaffold structure on which the work could be carried out wasn’t possible. The solution was to create a movable platform from which the work could be carried out – one that could be raised or lowered depending on the level of the river.
Similar problems affected the process of putting the concrete shoes into place for the new eastern ribs. Their shape and weight meant that casting them in place would have been by far the preferred solution on a bridge elsewhere, but the pier bases on which they sat were below the high tide point. Given the previously mentioned difficulties involved in heavy lifting from the surface of the Thames, lifting was far from an ideal alternative. In the end, the decision was thus made to build a casting platform for each section on the piers themselves but well above the water line. This allowed the concrete shoes to effectively be cast in situ, and then placed via a controlled drop.
The Bridge Slide
As the “before and after” diagram towards the top of this article shows, the new layout for Blackfriars effectively saw the bay platforms flipped from the east to the west. By changing the path the track takes onto the bridge, however, this changed the load dispersal pattern on the short bridge that connected the existing station infrastructure to Blackfriars Bridge itself on the northern bank. This resulted in the construction of a new bridge section, with safeguarded space for platform width expansion, being slid into place over the Christmas blockade in 2009/2010.
The track was finally slewed to the east over the Christmas blockade in 2010/2011. From this point, work began on the western half of the bridge. Here, the bridge structure was expanded outwards, with the nearest of the original piers being used to support the extra weight.
Whilst the presence of the piers made expanding westward easier, it also meant that the entire bridge deck needed to be relaid. This was not a complex process, but it was a lengthy one – especially given the presence of the live railway on the eastern half of the bridge. Ultimately this was carried out in a north to south sweep, with the graphic below giving a general idea as to the process.
With the bridge deck laid, the new bay platforms could be built. It is these that came into play last weekend, and the photos below show them shortly before completion. As has been commented elsewhere, in comparison to many other London terminals (particularly the reworked Kings Cross) Blackfriars features a low ceiling. This is sadly a necessity, brought about by the protected sight lines to St Pauls. Having checked with the engineering team, however, we can confirm that they are high enough (just) to allow OHLE. One additional consequence of the low, flat roof over the new platforms has been sufficient space to include an extensive range of solar panels. Whether these will provide the 40% of station power figure quoted by Network Rail remains to be seen. It’s a welcome development in looking to creatively use the space nonetheless.
Protecting the Underground
The purpose of this article is largely to highlight some of the complex – and interesting – engineering that has taken place at Blackfriars as part of its rebuild. As a result, we’ll take a more detailed look inside the new northern and southern entrances at a later date. One final element of the project worth looking at here, however, is the work carried out over the District Line during the rebuild of the northern terminal.
As we have covered before, the work on Blackfriars necessitated the temporary uncovering of the District Line station below. In order to allow work to continue without disruption to the Line, a steel Track Protection Structure was erected through which trains ran whilst work continued above.
The diagram above gives a good idea as to the nature of the TPS. Essentially, it featured a series of steel arches sitting on top of a steel base anchored to the platform.
With the TPS in place, the new steelwork for the structure above could be built around the District Line without disrupting the service pattern. This work was carried out with relative ease, although the shape of the site meant that it was impossible to lift the concrete support bars above the tunnel directly into place. As a result these were lifted onto one end and then, as with the connecting bridge above, slid into position.
Finishing the Job
As was indicated at the beginning of this article, Blackfriars is still not complete – although from a passenger perspective there is little left to be done. With the Olympics looming large, however, much of the remaining work will be deferred until after this summer’s giant School Sports Day. The majority of the engineering challenges have, however, already been met. We will visit Blackfriars again in the near future to look briefly at the new entrances on both north and south banks, but in infrastructure terms at least, it seems fair to say that Blackfriars is now essentially ready to face the future.