The cramped maze of tunnels that make up Bank tube station are about to change, as a set of huge new tunnels are being dug next to the Northern line that will transform the amount of space deep underground.

(click on the photos for larger versions)

When completed in a couple of years time, the narrow Northern line platforms will be much larger, a fast travolator will link with the Central line, and banks of new escalators will replace narrow stairs linking them to the DLR.

It’s an upgrade that’s being going on for several years, but almost all of it is hidden from view. There’s a building site near Monument, and what otherwise looks like just another office block development near Bank. However, unless you pay attention, it could be possible for even the most ardent of Bank station commuter to not be aware that on the other side of the corridors they squeeze along, huge new tunnels are being dug.

When completed in 2022, the station will be much faster to get in and out of, will have a brand new entrance on Cannon Street and will have a lot more space to wait for trains on the Northern line platforms.

Why is Bank such a complicated station?

Like a lot of the London Underground it wasn’t planned as a major junction, it just sort of emerged as one over the decades.

Initially the Circle/District line arrived at Monument in 1884, then 15 years later the Waterloo & City line arrived, followed in 1900 by both the Northern and Central lines. In 1933, Bank was linked to Monument, then in 1991 the DLR arrived.

Squeezing all these different lines into the space that’s already cramped thanks to the deep bank basements was a challenge, as was providing links between the lines so people could swap between them.

One thing to consider is why the station is so busy, which might seem an odd question to start with, but it can be illustrative when you look at the wider area. Yes, it’s right in the heart of the City of London, with a huge commuter base, but when you look at the area around Bank, the alternative transport options are surprisingly weak.

The nearest alternative tube stations are all on the sub-surface lines, so while great for those commuters, Bank is the only direct north-south or west transport option in this part of London. That puts a lot of pressure on the station to cope with those commuters.

Add in the Waterloo and City line and the DLR, and below ground, the narrow tunnels and different connections are often overwhelmed with people switching lines or trying to get out of the station.

In numbers, with nearly 62 million entry and exits through the station in 2017, plus the considerable numbers swapping between lines, Bank/Monument is busier than Heathrow airport. And getting busier.

With tube lines being upgraded to carry more passengers, one of the constraints to reducing overcrowding on the trains is how fast passengers can get out of stations. If the stations cant get people off the platforms before the next train arrives, you can end up having to close the station for a while.

It was that which triggered Bank station’s first major upgrade, back in 1960 when the long walkway from the Waterloo & City line was converted into a travolator,

Before the travolators were installed, it took an average 10 minutes to get from the platform to the street level during the morning rush hour, with the platforms often not emptying of passengers before the next train arrived. Following their installation, exit times were dropped to an average of four minutes, with no over-crowding on the platforms.

More about travolators later

It’s clear that with Bank station straining to cope with current demands, let alone future ones, and that something needed to be done.

Back in 2012 plans were proposed to upgrade the station, and these were then put out to engineering firms to see what they thought.

The core of the proposal is to dig a new Northern line tunnel to one side of the existing line, then reuse the old tunnel as a new corridor, massively expanding the amount of space below ground. This is a proven idea, as it was used at Angel and London Bridge.

What was to happen next was very unexpected. While three of the firms came back with modest changes here and there to make construction easier, less risky or cheaper, one firm, Dragados had clearly done a lot of thinking and came back with some innovative ideas.

It is fortunate that many of those ideas are now being put into action as they change what would have been a sizeable upgrade into something truly transformational.

The original plan would have seen the new Northern line southbound platform dug right next to the old southbound tunnel, and then the old southbound tunnel turned into a central passageway.

This is pretty much what happened at London Bridge in the late 1990s.

What we’re actually getting is a much bigger space, thanks to the addition of a new set of cross passages and tunnels between the old Northern line tunnels and the new southbound tunnel.

The extra space underground is being added mainly thanks to what’s going on at the surface.

One of the biggest problems in delivering the Bank station upgrade that had to be overcome is the lack of space above ground to do any work below ground.

Bank just happens to be in a part of London packed full of important historic buildings and narrow streets. In order to accommodate all the works needed to upgrade the tube station, they had to demolish an entire block of offices. Fortunately, there was a rather unimpressive block on King William Street that could be torn down without too many people mourning its passing, and while still a very cramped site to work on, does offer a few useful benefits.

The main one is that the block faces onto both King William Street and Cannon Street, which is a huge benefit for logistics as you can have lorries come in one side and drive out the other — which massively reduces congestion around the entrances and opens up more of the cramped space for working on.

What they also realized is that if some changes to the proposed layout were made below ground, there’s a rather useful second building site not far away which could be of considerable help.

When working underground, you often have to deal with old sewers and utilities, not to mention building foundations, but also occasionally, something old becomes very useful.

Not far from the Northern line tunnels is the remains of the original “northern line” that was decommissioned in 1900. What Dragados have done is to make use of that old tunnel as access to the Bank station upgrades. They’ve had to seal off a little used road nearby for their construction site, and drilled a large shaft down, but it gave them two building sites where it had been thought only one would be possible, and opened up a range of interesting other ideas.

In order to really make use of the old tunnels for the Bank station upgrade, they found that they needed to move the planned route of the new Northern line tunnel further away from the original path. That’s usually more expensive as you have to dig longer side-passages, but having the two Northern line tunnels further apart than planned opened up two of the more innovative ideas for this project, and the time savings from having two building sites more than compensated for the additional tunneling costs.

The travolator

One of the big reasons for there being sometimes quite long tunnels between platforms and exits in many tube stations is that they act as capacity sponges, allowing people to get off the platforms and away from trains, while waiting to get up the lifts or escalators.

But the longer the tunnel, the more annoying it is for people to walk down (ahem, Green Park), so here at Bank, they’re about to install a travolator linking the Central and Northern lines.

Where the original plans had a corridor squeezing into the curving line between the two Northern line tunnels, the much wider space now allows for a large, and importantly, very straight tunnel to be built instead.

And adding a travolator.

That extra tunnel that wasn’t part of the original plans added more capacity to the station to absorb passengers, while also speeding up the interconnection between the two lines it provides a lot more space so the tunnels feel less crowded. And it avoids the tedious climb up and down all those narrow stairs as the current station requires.

It was also almost entirely possible thanks to the second building site which made removing the extra muck easier than had they been stuck with just the one building site.

DLR escalators

At the moment, the two escalators and staircase leading towards the Bank side of the station for the DLR are hopelessly overcrowded at rush hours. But squeezing more in to such a tight space would be very difficult.

Studying passenger movements though revealed that the long corridor that runs between the two DLR platforms is only really used at either end, where the exits are. The middle is comparatively little used — and is just about the right length to fit in another back of escalators.

What will happen is that the DLR corridor will be cut in half, so if, for some odd reason you wanted to walk from Monument to Bank via the DLR, right now you can, but soon you wont. While the tiny handful of lost souls making that convoluted journey will lose out, the 500 people arriving on each train in the rush hour gain a set of escalators straight up to the Northern line, and to the new exit on Cannon Street.

That will massively speed up the time it takes to get out of Bank station if you’re a DLR commuter.

The plans laid out, construction starts

April 2016 saw works start on the two building sites above ground to get down to the tunnels.

The office block on King William Street had to be demolished, carefully, not just because of the nature of the area, but lacking anywhere for the staff welfare facilities, these were in the basement of the very building being torn down above their heads. Not ideal, and as soon as the block was taken down, decent staff facilities were put on the site.

When working in tunnels, which are very hot, noisy, dirty places, while wearing full protective clothing, gloves, goggles, carrying a heavy oxygen rebreather, it’s a challenging working environment, and good quality staff welfare facilities are essential. There are currently three 8-hour shifts per day working in the tunnels.

Over at the Arthur Street site, a lot of work went on to shift the utilities to one side to allow space for a deep shaft to be dug down. A lot of utilities. The side road being of use to the engineers has been of considerable use to utilities firms. Pretty much everything other than a gas mains was under the street and needed to moved. Then they found some Roman remains, so the archeologists had three months to explore the area.

The shaft is slightly unusual in having a rectangular top, to fit into the tight space, while allowing lorries to drive up to it to drop of fresh supplies, or carry away muck.

More than the building work itself, the most important thing in the success of a project is planning how the construction will work. When people complain why something can’t happen sooner, it’s often because several years of project planning need to be carried out to make sure everything will fit, on the day it’s needed, and that they can be removed on the day they need to be. That lorries wont turn up to deliver goods to a site that’s already full of other kit, the sites work with precise planning.

Digging a shaft down to the tunnels seems routine, until you need to check that all your kit will fit into the hole, and if not, and the hole cant be bigger, how does using a smaller machine impact on all the other timelines on the building site.

For the Arthur Street site, this was critical, as everything in the tunnels arrives, and leaves through this small rectangular shape — even one large digger that they decided to send down nose first to make it fit.

The tight space they have was described as trying to redecorate your living room with all the work taking place through your letterbox.

About half way down the shaft, the old King William Street station is proving to be a very useful storage site, and entrance to the main tunnels that are still another long walk down a set of metal stairs.

Down here a vast space opens up. We’re standing right in the middle of what will be the new Northern line railway tunnel. When completed, the shaft above our heads will be filled in again and never used again. Much of what goes into a construction site are the enabling works that permit the final tunnel to be dug, and are themselves never used again.

It would have been nice to reuse the shaft for ventilation, but it does sit in the middle of a road at street level, so that wouldn’t have been possible.

The new tunnel heading south is ready to be joined up with the existing southbound train tunnel, and the green haze you can see is the waterproofing membrane that is applied before the final finish is added to the tunnels.

The new Northern line tunnel has been largely dug now, but they are having to deal with a fully expected annoyance at one part — a building at street level is affecting the tunnel all the way down here.

The foundations to be exact. The new tunnel runs right though the foundations, and while they are able to just about squeeze it through between the piles along most of the route, there are four piles right in the way of the tunnel.

So, carefully, they’ve cut the bottom off each pile in turn, and that’s a sight you will probably never see again, the bottom of one of the huge piles that hold buildings up.

After the pile is cut out, the area is reinforced with a massive concrete shield that transfers the load back into the ground below the new tunnel. Cutting the bottoms off wouldn’t affect the building at street level today, but the big reinforcements are needed in case they ever want to build something bigger upstairs in the future.

When completed, the Northern line trains will pass through a massive concrete tunnel built inside the foundations of an office block. Which when you think about it for a moment, is not just really impressive, but shows how difficult it can be to squeeze additional spaces out of the ground under London.

Elsewhere, the new tunnel widens dramatically, for this is the new platform space. Much larger than the old Northern line platforms. Side passages are being dug to connect the two platforms, and in places the existing train tunnels are being dug out of the ground and exposed, ready for the connections to be made.

Part of the project is to dig a lot of new side passages between the two existing platforms, to link the old northbound platform to the much wider space being left behind by the old southbound platform.

This has been done by digging down between them from above, all by hand, and carefully taking away the soil between the two tunnels and then slotting in the necessary walls. As people lean up against the tiles of the northern line platforms waiting for a train, little do they realise there are people digging away just inches behind their backs.

A similar project is going on down below the Northern line as well, to create more side passages for the DLR to get to their new escalators.

Here we’re looking down at the top of the new side passage for the escalators which is being waterproofed before all this space is filled in again.

While the new double bank of escalators will make access between the street, Northern and DLR lines much faster and less crowded, probably one of the greatest changes in how people swap between lines is now being completed.

For the first time, we’re able to see the long corridor that will carry the new travolators linking the Northern and Central lines.

The entrance to the travolators will be around the middle of the platforms, which also reduces the crowding at each end of the Northern line platforms where the current exits are.

All this work is going on hidden from view.

What will make people who haven’t noticed pay attention is something that needs to happen in the summer of 2021.

When digging a brand new train tunnel, there comes a point when you need to link it up with the old tunnel. Ideally, you dig a very large cavern around the new and old tunnels, then over a few weekends break out the old tunnel and link the tracks to the new tunnel. As happened at Kennington recently.

That’s just not possible here largely thanks to the aforementioned deep foundations. What will happen is that in the summer of 2021, a section of the Bank branch of the Northern line will close for roughly 3 months.

When that happens, the old southbound tunnel either side of Bank station will be filled in with a soft concrete foam to stabilise them, while the new tunnels are drilled into the sides of the old tunnels.

Only then can the tracks can be joined up.

While that’s going on, at Bank station, the old southbound tunnel will have it’s tracks filled in and turned into a new large concourse, while the currently hidden new side passages are cut through into the old northbound platform and finished off.

Come roughly September 2021, after a few months of closure, people will arrive at Bank station and see these huge new tunnels, the new escalators down to the DLR, the travolator to the Central line.

Blimey, some people might think, they did all that in just a few months. When in fact, it’ll be the culmination of years of planning and construction, and roughly £600 million being spent to make our journeys less of an ordeal.

When finished, around 1,213 metres of new tunnels will have been dug deep under London’s streets to turn the Bank tube station upgrade project into a reality.

Thanks to all the staff at the Bank Station upgrade project for taking the time to show off the work they’re doing.

Some more photos