How giant tunnelling machines work

Is this magic? Cause I'll be damned if that was not a magic wand at the start!!

Fun fact: It was legendary French engineer Marc Isembard Brunel who pioneered this technique of using a tunneling shield in 1818, and he later used it to successfully dig a tunnel beneath the Thames, completed in 1843.

His son, Isembard Kingdom Brunel, also became an engineering legend in his own time, but that's a story for a different thread.



Each machine has a rotating cutter head at the front, and a series of trailers behind, housing all the mechanical and electrical equipment required for the excavation of material.

Each TBM weighs approximately 1000 tonnes and will be up to 140m in length with an external diameter of 7.1m. This allows for an inside tunnel diameter of 6.2m once the concrete tunnel segments are in place.

Each TBM will be operated by a 'tunnel gang' comprising of around twenty people - twelve people on the TBM itself and eight people working from the rear of the machine to above ground.

The weird thing is that you could start his son's description as "legendary British engineer Isembard Kingdom Brunel". He's responsible for a great many pieces of British Victorian engineering.

Avatar anyone?

Boring gif

I hear that they often just abandon some boring machines past the end of the tube because there's no viable way to back it out, turn it, or lift it out. There are a lot of mountain tunnels that immediately change to elevated track/roadbed/bridge as it emerges from a slope. I would like to know more about the logistics of tunnel bore starting and ending situations.

Well, there is this video from the magic wand factory, and the way they make the wand is eerily similar to how giant tunneling machines work.

One of the Channel Tunnel TBMs was driven into a hole in the middle of the English channel. Bertha in Seattle is going to be disassembled (it just emerged from its tunnel about a week ago!). There's no other project needing the same size and design, so it's not worth keeping. I think Sound Transit has been using the same two TBMs to bore quite a few of its tunnels, because they're all the same diameter for trains.

And before they had that technology, they just used Alaskan Bull Worms to do all the tunneling.

Oh, I almost voted you down, then I got it. Well done, sir/madam.

but they cost a fortune to buy and operate

Yet after the tunnels were done they sold one of them for £40k and had the other one dig itself into the ground where it rots to this day.

On a conveyor belt heading out the back so it can be dumped in carts or trucks and taken to the surface

Tunnel Boring Machines (TBMs) can go on the order of 10m per day, but that probably depends on the size of the machine and what it's boring through. Or whether it hits any underground pipes and has to be repaired haha.

They use electricity, although the movement of the drill part is hydraulic (powered by electricity).

The machines used for the channel tunnel are the most precise boring machines ever developed, but they cost a fortune to buy and operate, and their precision is excessive most of the time. As such only two have ever been built. One bored from Dover, the other from Calais, and neither has been used for anything since then.

* must have * must've * must of

Ba sing se must of been the test.

Giant robot worm train. Got it 👍

Each TBM will be operated by a 'tunnel gang'

That's us! And we rule!

Heck no, there are multiple humans within. The concrete blocks don't just lock into place, they have connecting bolts that are hydraulically drilled (by hand). There are also many other parts of the process that need human observation - pressures, rates of motion, ensuring the excess grund is conveyered away smoothly, etc. Large teams of skilled workers.

My first thought too.

What kinda energy does it use?

How fast is it? let's say for example how long until it moves/digs 10 meters?

You've never been to European cities with your car then ;)

So you're saying he's the greatgodfather of steam-punk non?

Where does the dirt go?

Fuckin Bertha

This kills the nature.

Interesting gif, boring machine.

Yes, they often abandon it after it finishes it's job. The machine is usually designed specifically for the planned tunnel, according to the geology, width of the tunnel etc., and can't be used anywhere else - each tunnel is usually different. These machines are used when the time spent digging the tunnel the conventional way would be long or it would be too complicated, and it's more efficient to just design and construct a specific machine. (I am a geologist, so I know a little bit about them)

Soil tests at some intervals are made before the project begins.

I believe the French kept and have reused the TBMs they used in the channel tunnel, even going as far to give them nicknames.

I'm still curious how long it took to get that thing to Ba Sing Se. That bitch had to be in transit for years.

The real magic is making sure you're digging this beast in the right direction and angle.

/u/rukuto is correct, but in addition the walls of the tunnel are self-supporting. Those concrete pieces you see are strong like an arch bridge so they take the weight of surrounding soil/rock and prevent collapse. Tunnel builders can also use shotcrete (concrete that can be sprayed onto surfaces) to create and seal tunnel walls, depending on the rocks and the tunnel.

Oh god, can you imagine being the guy responsible for getting the math right.

"Perkins was off by a 1/128th of an inch when we started and well, long story short, we just bumped into the Hudson."

Oh yeah, I had completely forgotten about the self burial.

I read this in Steve Coogan's Saxondale voice.

Good god, dear sir - I do believe those are eerily similar!

I thought it was perfect. They even showed the stockyard to show how large each one of those panels were.

This is cool, but how d they know that the ground is not loose and wont cave in on them?

Or does it not matter because the placed supports maintain the tunnel no matter what?

Hahahaha holy shit kind of morbid

Maybe they weren't powerful enough, or were exhausted by the transport work. Or Azula lost her temper with them and killed them.

I'm guessing he means for stuff like plaque build up.

two TBMs went from Dover (Shakespeare) and two went from France and a fifth went north from Shakespeare's cliffs towards the rail depot at Folkestone and I think that was the one that was by the side of the motorway ? - I forgot the service tunnel which also had two TBM digging from each end.

Actually, it broke even several years ago, and is currently making a profit. Ie, paying back the construction cost, with interest, operating costs, and having money left over.

It would have been transported in pieces, then assembled in safety just outside of ba sing sei to drive the last stretch.

Using inches.

There's your problem, right there.

In Norway, every new tunnel is first sprayed with shotcrete and it is also injected into the rock. Problem is, many developers use an insane amount of pressure when injecting it into the mountain, sometimes it comes bubbling to the surface.

There is no war in Ba Sing Se.

And right at the front of it is Archimedes' screw, still doing a damn fine job 2300 years later.

Bertha goes about 10m every 2 years.

Big spinny disc at the front grinds rock, which is sent backward on a conveyor belt.

Part of the machine puts panels in to help secure the tube.

Does that help?

The design and maintenance probably cost many times more than the machines themselves.

Thank you! This posting-gifs-instead-of-videos mania is starting to wear me down. This is utterly worthless w/o sound.

You have to consider these things probably cost a fuckton on upkeep if you want to have them operational. And you never know when the next tunnel needs to be dug with exactly those specifications of the machine.

Also getting them out of there means having to disassemble the thing and haul 1000 the tonnes of equipment out that hole

One day, we'll be able to do the same for veins and arteries.

Is Isembard is Steampunk Jesus, then Marc is Steampunk God.

I know it's probably quite safe working there, but for some reasons it sounds scary.

Is this completely robotic like the video suggests? No human interaction on-site?

Is this why Elon Musk said that there were similarities between SpaceX and his boring company? In that currently the machinery is not reused between jobs, which drives up cost immensely

I'm pretty sure it gets made into slurry

I'd call it engineering porn.


Jesus, how much do these cost?! I can't imagine just abandoning something like this haha

Well the machines should be more fun then!

10 m per day is a pretty boring job...

But wouldn't they just use the earth benders to, ya know, just open the wall?

Did you notice that they showed 2 types of machines, 1 for competent ground with the auger and the other where they are using a slurry based system. Very cool machines.