I’m in a huge tunnel deep beneath Austria.
Soon cars are going to zip through here without realising that this space used to be solid rock.
And that’s all made possible by this massive 250 tonne piece of kit.
You won’t find this on many construction sites.
It’s a one of a kind machine that was built especially for
this project … because this isn’t how you’d normally dig.
If you’ve ever been driving through a tunnel and wondered how it got there,
and why it isn’t collapsing … It's because of seriously impressive work like this.
Crews here are pushing day and night to carve a path that better
connects this Austrian city with a massive new suspension bridge.
It’s a challenging, twisting and high stakes infrastructure scheme
that’s about to impact the lives of millions.
Now, if you want to get around here in Linz, you could take a streetcar, cycle, walk or drive.
But there aren’t many ways to get across the Danube.
So the city is building a brand new 305-metre-long suspension bridge across the Danube.
But to build above the water, first they have to actually get up there first.
And there’s a little problem standing in the way – these massive solid rocks.
So the team here in Linz is tunnelling through
them to connect the existing highways up to the new bridge.
They’re basically trying to build a simple slip road – but inside
a massive hillside formed of solid rock and on both sides of the river.
Now here at The B1M we kind of know a thing or two
about how to build a tunnel. Time for another quick engineering 101.
First choice for a tunnel nowadays is probably going to be a tunnel boring machine, or TBM.
You know the ones – they’re massive tube-like machines that eat through rock,
seal and line the newly formed tunnel with prefabricated concrete segments all in one go.
TBMs are great because they’re efficient and can travel underground without anyone
living above really noticing. Like under ancient woodlands
or beneath the city that never sleeps.
But they’re pretty expensive. The nearly 1,000 tonne TBM used on London’s Crossrail cost £10M.
So if you’re splashing out one of those bad boys, you better be getting some serious mileage in.
And since they can be so big – and we mean really big,
up to 15 metres wide and nearly 200 metres long big.
They’re great for tunnelling long stretches of a relatively straight path.
Sounds like a no brainer for a big infrastructure project, right?
Well yes, but here’s the site in Austria.
Just 1,600 metres of twists and turns through solid rock along the bank of a river.
So rather than trying to manoeuvre a giant TBM through it,
construction here went a little more like … this
This is the alternative and quite frankly much more fun way to build a tunnel.
Granted, it’s not quite so subtle, but it gets the job done.
In incredibly simple terms, you drill some holes in the rock, drop some explosives in, stand very
far away, hit a button called “detonate,” clear out the rubble and repeat until you have a tunnel.
The tunnels here in Linz were built using the New Austrian tunnelling method. First the path
was cleared using drill and blast, with the debris taken away by boat along the river.
Then a whole load of anchors and drainage points were installed, concrete was sprayed on the walls,
and these giant yellow waterproof sheets were added to help seal it off.
But that’s only half the battle. Once the tunnel
is cleared the team has to line it to get that nice smooth finish.
Now you might think it would be cheaper and easier to just leave it as exposed craggy rock, and that
would be the case but that’d be pretty dangerous and would create a long-term maintenance issue.
Rocks could fall at any point over the tunnel’s lifespan.
What you want is it looking nice and smooth like this.
That’s where this thing comes in. It’s an absolutely massive 250-tonne piece of
equipment developed by PERI Formwork Systems called a formwork carriage,
and it’s been custom made for this site.
This is our formwork. We
used it to concrete the whole tunnel, the walls. We used it for over 180 different sections. Wow.
Here’s how it works.
First all the parts of the machine are brought in by truck and assembled.
Then workers first prepare the machine for the day by shrinking
it down enough to move through the tunnel.
They’ll remove the front bit called the stopend, close the wings, lower it down
towards the ground and roll it on through. Once it’s inside the bit of tunnel that
needs to be lined, the wings will expand until they’re very close to the hard rock.
Concrete is then pumped up and through into the space between the formwork and the rock,
moulding into the smooth curved shape of the formwork to give the tunnel its nice lining.
Then it’s a waiting game.
The concrete needs to cure overnight so the formwork stays in place until the morning when it
can safely be shrunk back down and moved forward to the next bit of tunnel that needs to be lined.
Even the slightest delay in the schedule during the day means the concrete won’t
be cured by the morning, which means the whole project getting thrown off.
No pressure then.
What's been the hardest part of this project from your perspective?
So we have not a lot of space to work with.
That's a really tight curve, the inner side of the curve is shorter than the outside of the curve.
So we had to adjust the formwork to concrete on one side, a longer
section, and on the other side, a shorter section.
Now when it’s at its full length, PERI’s machine can work in 12 metre stretches.
But because there are such tight corners to this route … sometimes
the team needs to cut the machine in half and pour even smaller 6
metre slivers of concrete to create a curve in the tunnel.
You wouldn’t be able to tell from far away, but if you look up close here you can see
that this curve is formed by a bunch of smaller sections fused together to create that angle.
What's been the best thing about working on this project? What have you most enjoyed?
Every day brings a new problem. Something new to think about.
When it completes, millions of people will pass through this tunnel,
and the immense effort that went into building it will be taken for granted.
It shows once again the power of construction to shape our world,
and the amount of innovation that’s sometimes happening right beneath our feet.
This video was made possible by PERI Formwork Systems,
you can learn more about them and their massive machine at the link below.
There’s also the chance to go even deeper into this tunnel and the other topics on our channel
over on The World’s Best Construction Podcast – available now wherever you get your podcasts.
And as always , if you enjoyed this video and you want to get more from the definitive video channel
for construction, from the channel that takes you down Austrian tunnels, hit that subscribe button.