It may not look it from the outside, but an important part of Crossrail’s Canary Wharf station has already been completed – and five months ahead of schedule.

In fact it doesn’t really look completed when you have a look at it – but what the builders have done is finish the structural construction in order to hand it over to Crossrail engineers to start fitting it out. Over the next few months they will be laying tracks on the base of the station so that when the tunnel boring machines arrive next year, they can drive through the station and out the other end.

There will in fact be a four-month rest inside the station as the engineers take the opportunity to carry out some maintenance work before they carry on tunnelling west towards Farringdon Station.

As – in construction terms – a milestone has been achieved, it was a chance to go back inside and have a look at what has changed since I last saw the bottom of the station, which at the time looked a bit like this:

It’s possibly worth reflecting on the construction method a bit, as people who live and work locally who have been watching the site probably wont be aware of how deep the site actually is.

The station sits in an old dock, which was drained and then they started building on top of that base – but what was then hidden from view is that they also started digging down as well as building up. In fact, they went down the equivalent of about 4 stories to get to the bottom where the trains will run.

This construction work is largely hidden from the public watching from the sidelines, who otherwise might wonder why it took two years just to build a couple of levels of flooring inside the docks.

The site visit was one that took us straight down to the very bottom of the station, with limited time to snap a few photos of the intermediate floors, which are frankly, just big open spaces at the moment. Down one flight of builders stairs, a walk along the station then down another flight to get to the bottom.

And finally you can get to see the base of the building, and the vast area that has been dug out of the ground for the trains and platforms.

Once finished, the platform level will lose some of its height as the tracks will run at about the same height as the man’s head is in the photo above. You’ll also lose a little bit at the ceiling for fittings, but it will still be a very impressive space regardless.

The box itself is 30 metres wide and some 250 metres in length. If you lay it on its side, you can actually fit the famous Canada Square skyscraper inside the station, with space to spare – which might be a more impressive way of thinking about it.

The tunnel boring machines will start digging from the Canning Town area later this year and arrive at Canary Wharf early next year. They will arrive, hopefully on target at these two prepared rings, when they will then run on rail tracks across the station to the other end and engage in identical rings to begin tunnelling again.

To put it into context, this is what the site looked like last year.

All the Thanet Sand has been covered over, so no chance to play this time and the rough Giken Piles that were initially driven down have been covered in smooth concrete.

The use of Giken piles was interesting, as they can be slid into soil almost silently, which is a boon for the offices right next to the building site. They were also essentially watertight, which is vital to hold back both the dock/river water, but also to hold back the lower aquifer as they drained the soil of water to allow digging down.

Most of the Crossrail stations will be built after the tunnel has passed their location, but Canary Wharf is, evidently, the other way round. This is partly to take advantage of the box design, but also due to a safety issue. If you are building in a dock environment, it is better to have the station box watertight before the TBM arrives, otherwise later construction carries the theoretical risk that the Thames will drain into the tunnels.

As we were on site, some equipment belonging to the builders was still being removed, including the mobile hoist unit, which was itself hoisted up and out of the station by a surface crane while we were there.

The boxes you see around the columns, they are basically the platform level. The space below will be in-filled with services and eventually track ballast for the trains to run along.

As all construction site visitors will be aware, it is necessary to pay homage to the tunnel portal when visiting as seen below – and for the avoidance of doubt, that was a joke.

Back up at surface level, I learnt a few new snippets of information I wasn’t aware of before.

As mentioned, the station sits inside the dock, and as I was aware, the north side will be re-flooded eventually, and will form a navigable channel for boats. Small boats.

I had presumed the same would happen on the south-side, but no – it will be slightly flooded, but will in fact be a sort of wetland nature reserve running the length of the station. This is more strategic than tree-hugging.

Despite the vast size of the station, and the mega-tonnes of concrete in it – water is still more powerful. Should the dock gates fail, during high tide, then the southern channel will be designed to flood and the weight of the water there, balances out the additional weight of water around the rest of the station. OK, the station is hardly going to float down the Thames, but it could shift an inch or two without that flood channel.

The pedestrian bridges over the channel will also be designed to absorb the movement.

It is slightly humbling to remember that for all the might and scale of the human construction seen here, the river is still more powerful.

The concrete beams in the photo above will carry a pedestrian passage along the outside of the station at shop level.

I also wasn’t aware of it, but underneath the KPMG office block is a tunnel that will link the station to the current Canary Wharf shopping centre. It was put in when the office block was built, in expectation that the Crossrail station would arrive, eventually.

Quizzing the site manager as to where the tunnel enters the shopping centre delivered a bit of a shock. The coffee shop I usually use actually sits inside the tunnel entrance – so around 2017 when final fittings are taking place, I lose my coffee shop!

A load more photos from today’s site visit here. Thanks to Crossrail and Canary Wharf as usual for the invite.

I also look a look around last May, when it was more mud and less concrete – the article for that is here.