King’s Cross tunnels & canal aqueduct #2

King’s Cross tunnels & canal aqueduct #2

That darned canal aqueduct at King’s Cross is a major factor why the railway layout at this prestige London railway terminus has problems. Its not just that, there’s also the Camden sewer which also caused problems too by being right across the entrance to the three Gasworks tunnels. As we have seen, that sewer was realigned and modded so a better approach gradient could be facilitated into the station itself. But the canal aqueduct itself simply cannot be altered – not without a truly massive engineering headache that would entail all sorts of deep excavations, the total closure of King’s Cross station for many months (along with the local roads and the canal itself), and thus the storey of the King’s Cross #EastCoastUpgrade works has essentially been about the art of trying to squeeze a more advanced system into a more advanced system.

In terms of the Regent’s Canal/Cross King’s station interface, there’s nowhere else on the canal system (or on the railways) these days where both canal and railway are in such close conflict, not even places like Birmingham, so the arrangement at King’s Cross is perverse in how it actually came about, yet it’s intriguing as well as archaic – and that because no one in their right mind would put both canal and railway in such close conflict. However, it is also architecturally and historically interesting because it is one of those odd Victorian contraptions that still serves a purpose one and three quarters of a century after it was built.

It is said that King’s Cross station was one of the most difficult to leave due to the dip immediately beyond the station platforms and down under the Regent’s Canal. Even the highly regarded Deltics (Class 55), as well as the A4 Pacifics, struggled at times. It was difficult to see in these tunnels at times, so lights were installed after one accident in particular, which resulted from a train slipping back. These lights alerted drivers if their trains began to slip. They were merely positioning lights and if a train began to slip back down the gradients in the tunnels, well the lights would be moving in the wrong direction and that alone would alert the train drivers in the murky depths of the tunnels something was amiss with their train!

The work to ‘upgrade’ the station throat in the 1970s

Crepello at Gasworks Tunnel in 1976. This view is taken from the York Road platform. Notice how the platform itself actually extends into the tunnel. Source: Wikipedia

The old King’s Cross signal box was demolished in early 1976 and a temporary panel was established in the new power signal box to control the old layout until the remodelling was completed. That’s when the lines to Moorgate were closed and the eastern Gasworks tunnel taken out of use.

London Kings Cross 5th March 1977

Picture of The Cross in March 1977 before the remodelling works began. One can see the gradient that begins through the centre Gasworks tunnel. Despite the very generous headroom in the tunnel judging by the portals, that inside the tunnels themselves was very limited, barely being much above the roof of the train itself! Source: Flickr

King’s Cross poster 1977 advertising the work which would take nine weeks. One can see from this the amount of pointwork (and single/double slips) that were sited on the steep gradients into the tunnels. Source: Twitter

The rationalisation of the tracks out of the station was one of the outcomes of the 1977 works. This was during a period when the UK’s railways were in general decline. Six approach roads were no longer required, so the eastern tunnel was decommissioned. Surprisingly, just six years later, plans were proposed for a single track to be laid in that tunnel to help with capacity at the station. This was never carried out.

There is one minor reason why the eastern Gasworks tunnel would have been decommissioned in 1977. This is due to the fact that the headroom under the Regent’s Canal is slightly less than in the other two tunnels, and with the OHLE technology available at the time, the tunnel’s roofs could not be raised as much as a road bridge can. This was nearly forty years before the GWR’s Steventon bridge problem forced a complete rethink on the tightest parameters an OHLE system could offer. In fact, contact rail was originally planned for Steventon to allow for 100mph/160kmh running, but experiments revealed that the same speeds could be achieved within tighter parameters using contact wire.

‘Smiley’ 365517 arrives at London Kings Cross railway station in July 2009. Note the steep gradient out of the western tunnel. Also the double slips are very much evident in this view. Source: Wikipedia

Of course, there will never be any 100mph running at King’s Cross! Line speeds, on the other hand, would be increased through the station throat and the tunnels themselves. The maximum speed allowed in the centre tunnel is 90 km/h (55 mph). The new eastern pair of tracks would travel at a speed of 75kmh or 46mph, while the western bore (pardon the pun) would travel at the slowest of all, at 65kmh or 40mph. According to the plans, the centre tracks would be the fastest of all, reaching 130kmh or 80mph by the time a train entered the Copenhagen tunnels. Again, in order for any of this to be possible, OHLE design had to become far superior than it had been, even to the point where it could be more individually tailored to suit the various tunnels, as opposed to the standard catenary product of the 1970s and later. Some of the original OHLE gantries from the 1970s were retained for the King’s Cross upgrade, a few were modified, and the rest was completely new.

The tunnels and canal aqueduct as seen before and during the East Coast Upgrade

Note: This section is in two parts.

As most people are aware, the East Coast Main Line was closed on a number of weekends and extended bank holiday periods throughout 2020 and the first half of 2021 to allow for upgrade work and the reopening of the eastern gasworks tunnel. The following sections cover the work to reopen the eastern gasworks tunnel – with the added bonus of the Regent’s Canal aqueduct! As previously stated, this structure would obstruct the scope of work that could be done to reopen the tunnel as well as any upgrades to the King’s Cross station throat.

The King’s Cross closures were regularly announced. The many different colourful posters and adverts would merit a whole post alone! Source: Twitter

According to a number of documents submitted as part of the proposals, the Gasworks tunnel eastern bore closed in 1972. In fact, the year was 1977. In any case, one of the primary reasons for the King’s Cross upgrade was that the 1970s signalling had reached the end of its useful life. As a result, it was decided to renew the signalling on the approaches to King’s Cross, as well as to undertake track alterations and new track over a mile and a half from the buffer stops at King’s Cross. This would also correspond with the transfer of control from King’s Cross Power Box to York ROC. I wrote a little about that here.

The diversion of the Camden sewer was one of the other works that enabled the site to be regraded. I won’t go into detail, except to say that it was realigned so that the station area and gradients could be improved. The sewer originally ran in a straight line across the station throat, from the south west corner of the western Gasworks tunnel portal to the road junction at York Way/Wharfedale Road. Some may have noticed that the York Way platform and tracks had a steep descent to get underneath York Way itself en route to Moorgate. Yes, the Camden sewer was a stumbling block! At the time, the done thing, a sort of solution, was to take over the Finsbury Park to Moorgate line from LT (that in turn had been prompted by the building of the Victoria Line which took out the tunnelled route south of Finsbury Park to Drayton Park.) Thus, the removal of the Widened Lines connections provided British Rail with some additional but limited space to improve the track layout. I say limited because the area was still constrained by the Camden sewer (as well as the tunnels.) The powers that be at Network Rail, no doubt, decided that this sewer had to be fixed if this work was ever going to be considered a good quality upgrade.

The tunnel and the canal aqueduct well before any upgrade was mooted. Its interesting to see a rough sort of pedestrian walkway was marked along the right hand side. This is because the tunnel continued to be used as vehicular access for maintenance work in the locality to the north.

The Regent’s Canal aqueduct seen in its full glory! The survey reports claimed it was in good condition. After nearly 150 years of use I expect it was remarkable the structure had held up so well despite its somewhat tardy appearance.

Both these images were from small pictures (400px max) found on Network Rail documents. I upscaled, cleaned up and and enhanced these small images. Thus those shown are several times larger and they’re not originals.

One of the early stages of the work was to dig out the existing permanent way foundation. It wouldn’t have been suitable for a concrete trackbed which was proposed, not only that it needed to be re-levelled somewhat to permit slightly better gradients through the tunnel.

The eastern Gasworks tunnel without a permanent way base. Part of the canal aqueduct can just be seen at top of the picture. Source: Twitter

Monitoring equipment in the tunnel underneath the aqueduct. The picture clearly shows how the cast iron aqueduct is laid upon the top of a series of stone plinths laid lengthwise along the top of the tunnel’s brick wall. Source: Tunnelling Online

I upscaled the above image and then enhanced and cleaned it up to show the actual foundations of the canal aqueduct itself much better than it had been previously rendered.

During early surveys, the disused Gasworks tunnel was discovered to have large amounts of water ingress, which the surveyors attributed to the Regent’s Canal. Because of the water seepage, the pointing between the brickwork was in generally good condition. The cast iron aqueduct was also deemed in good condition. Significant amounts of moss and bryophyte were discovered, and parts of the tunnel’s arch were missing bricks.

During the process to restore the structure and construct a new track foundation base, five laser monitoring stations were erected in the abandoned bore. Even the bottom of the Regent’s Canal aqueduct was inspected as the work progressed to ensure there were no movements. You wouldn’t want all much water to go into the tunnels, would you? In effect, any work at King’s Cross is treated as though it were done with kid gloves – all because there are millions of gallons of water just a few feet above!

The project was meant to be completed in March 2020. As it turns out it was 14 months late.

Early work to build a new permanent way base in the eastern Gasworks tunnel. Source: Twitter

The eastern Gasworks tunnel looking north after its new track foundation had been laid. Source: Tunnelling Online

Work underway in the western bore showing part of the canal aqueduct. Source: Twitter

Work underway in the western bore showing the canal aqueduct. This was the best Network Rail image published on social media of the aqueduct itself. Source: Twitter

Its interesting to see the later tunnel consists of an aqueduct made with a cast iron base the same as in the other two tunnels. Instead of cast iron plates laid onto stone plinths, brick has been used here. Its probably engineering bricks for all I know. These indicate its merely the clay puddling on the canal bed that stops the canal from leaking! It must be an extremely strong and rigid structure because water plus clay puddling plus bricks is an extremely heavy combination of materials!!

As explained in the first part of this article, the construction of the western bore was in fact accompanied by new tunnelling methods, including underpinning. This presumably is one reason why it was deemed a brick structure would be able to hold up the canal aqueduct rather than having to use stone lintels as in the earlier two tunnels.

Almost the entire Gasworks tunnel can be seen here. Its a very gentle gradient this side of the aqueduct (seen in the distance.) It will also be seen this particular tunnel is in fact somewhat bigger than the other two – although I’m certain it has a somewhat more oval profile too. The picture shows the track bed after an initial top layer of concrete has been laid over the aggregate foundation base pictured earlier. Source: Twitter

North end of the eastern tunnel. August 2020. It can be seen the Regent’s Canal forms a considerable impression upon the course of the railway tunnels. Source: Twitter

Gasworks eastern tunnel with the first sections of track laid. View looking north from near the canal aqueduct. October 2020. Source: Twitter

With the reopening of the eastern Gasworks tunnel, it’s now easier to obtain slightly steeper slopes out of King’s Cross station. Rather than having a complicated configuration jammed between the platform ends and the tunnels itself, the new arrangement allows for softer grades. All of the new platform extensions feature a modest incline into the tunnels, while the platforms themselves have somewhat varied levels on either side depending on track geometry. Throughout the station’s surrounds, the former platform parts are level with the railway at roughly 15 and a half metres above sea level. Partly because the existing station areas are historically significant, any modifications would be difficult, and I believe a fuss would have been made if the idea of rebuilding these platforms had been floated. Yes, the old platforms have new surfaces, but with a few exceptions, they cannot be structurally altered. Platform 0 is an exception because it is not an original part of the station, but there are a variety of reasons why it was required, so there was a valid case for its construction.

Platform eight, for example, is built with original York stone from the 1850s, while the brick structure beneath it was designed by Lewis Cubitt. Other factors include the train shed, its supporting pillars, and the rest of it; there is a long list of historical elements in fact, which is why Network Rail is unable to change the station’s overall structure. Even the new signalling introduced as part of the upgrade had to be approved in accordance with the station’s historical configuration. The new platforms are outside the station’s historically significant boundaries, and because they do not have a material impact on the historic station, Network Rail was able to incorporate a very slight gradient into the new platforms where they meet the old platforms – giving trains an advantage when tackling the gradients through the tunnels. I must admit that despite having walked on these new platforms a few times, I had no idea they had a gradient.

Photograph I took of the new platforms a day or so after this side of the station had been reopened. One cannot tell there’s a slight gradient in these platforms and tracks!

A significant portion of the pointwork that switches trains between the different tracks is now located at the northern end of the tunnels, allowing trains to switch over on gentler graded sections of track. Some may find it strange that a new tunnel increases capacity, especially since it connects to the four-track classical system built in the 1970s. However, the increased capacity is accompanied by increased reliability and faster exits from the station, so the fact that it switches from a six track formation to a four track formation beyond the three tunnels isn’t that significant. In fact as has been mentioned earlier there was a proposal in 1983 to introduce a single track through the now closed eastern Gasworks tunnel to assist with any capacity issues, but again it didn’t entail a full six track pack from the north of the tunnels towards Finsbury Park.

Network Rail’s engineers practically never mentioned the Regent’s Canal or even its being an ever present problem – except in the following tweets. The first we have seen these pictures before however the tweet itself does briefly mention the Regent’s Canal.

They also mentioned it here but its basically a rehash of the above tweet!

In this next Tweet network Rail admitted the King’s Cross Upgrade wasn’t an easy job with the Regent’s Canal in the way – because of the very tight clearances imposed on the equipment that could be used in the tunnels. If one thinks about it, even though the track has been modded and the gradients eased its still a very tight squeeze and that in many ways is why the western gasworks tunnel has more strict speed limits than the other two.

One of the pictures from that tweet shows the Kirov crane carrying a section of track. What’s interesting is this is being carried as level, however the existing track’s steepness as it descends into the tunnel is very obvious – its an excellent illustration of the gradients necessary to pass trains underneath the canal. Source: Twitter

One more mention by Network Rail of the canal. At least they confirm visually there’s more than just a bath tub of water up above!

As can be seen, the steep gradients that lead down from the station area cause a slew of issues. Even though the Camden sewer has now been relocated south to its new location, the gradients still do not have much extra leeway. It has helped, but it is still a less-than-ideal layout. One could argue, “Well, that’s the canal’s fault!” I don’t believe so. Rather, the people who designed the railway in the 1850s are to blame for the current state of affairs. Of course, they could not have predicted how the railways would evolve, with electric trains, overhead catenary systems, high-speed trains, and so on.

However, there were some caveats that could have been designed out in the 1850s. If an aqueduct had not been required, the lines could have easily been levelled into King’s Cross. That, however, was not the case. Indeed, one wonders why the railway’s engineers did not consider building the new station slightly below ground level (like Liverpool Street or Paddington), as this would have avoided the steep gradients required and also made future upgrades to the layout much easier to achieve. The desire to have the new terminus absolutely level with the streets outside the station was obviously a huge factor, and the Great Northern knew it would draw crowds – which is why its tracks were built at a certain elevation. That particular elevation wasn’t really an advantage because it required some rather difficult rail approaches that had to dive under the bottom of the Regent’s Canal.

‘The Great Northern’s experience with its London terminus at King’s Cross was one of the most unfortunate . Opened in 1852 the station was cramped and the approach lines, through the Gas Works and Copenhagen tunnels, steeply graded.’ (Source: Google Books)

How the Great Northern’s terminus station originally looked. It was a fine and imposing structure and passengers and horse drawn carts and coaches had absolutely level access from the streets onto the platforms. It however meant the tracks had to be at a certain elevation which meant the whole thing was in fact very awkward. Source: National Railway Museum (Note: Their blog has been deleted thus an archived image is used here.)

The new station, which opened in the 1850s, was attractive and gave the railway company a status that the other London termini did not have. However, it has been a major annoyance and comes at a cost in terms of future developments and upgrades. Even if a very slightly sloping station had been built in the 1850s, it would have gone a long way toward solving the problems. There was clearly a lot of oversight in terms of how the Great Northern Railway and the Cubitts designed their fine new terminus back then – and the railway is paying for it, as evidenced by the recent #EastCoastUpgrade. There’s no doubt that King’s Cross is a fantastic terminus; it’s architecturally interesting and its history is fascinating; it’s home to many of the most famous named trains in the UK, as well as the world’s fastest steam trains. Unfortunately, the magnificent station comes with a number of caveats any modern railway engineer would prefer to avoid.

This article is continued in Part Three.

Links to the other King’s Cross Aqueduct pages:

King’s Cross Aqueduct #1

King’s Cross Aqueduct #2

King’s Cross Aqueduct #3