How Tunnel Boring Works (2011) [video] | Hacker News Reader

How Tunnel Boring Works (2011) [video]

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73 pointsrkagerer30 comments

Absolutely fascinating! After watching all that CGI, I wanted to see an actual machine in action and came across this video:

https://www.youtube.com/watch?v=qlrZ3G0tAzY

it's by the company that makes these massive boring machines.

Interesting stuff.

One thing I was hoping the video would touch on is how do they know exactly where they are and how they are oriented while boring large tunnels? If you're digging 30km of tunnel, being off by half a degree in any direction would be disasterous, no?

Survey control is transferred down the tunnel from surface. How it gets down there depends on whether you launch from a shaft or pit, but once survey control is established in the hole it is straight forward to locate the TBM using standard survey techniques (eg - survey prisms). The TBM has a reflector that can be shot with a survey instrument to accurately place the machine head and the TBM itself is equipped with gyroscopic or accelerometers for backup control if survey is lost during mining.

Why is the video unlisted? Very rare for a 1M+ view video to be unlisted.

The pipeline video is fascinating, too. They coat the exterior of the pipes with a lubricant, and install new segments at the back end, thrusting the entire line forward each time. https://www.herrenknecht.com/en/products/productdetail/85/?w...

I wonder how software is engineered for those machines. Languages used, etc.

Not sure if I missed it but how do you bring this kind of equipment underground in the first place? Do they have to dig a huge hole using traditional methods first?

Yes, they have to build a shaft. One way is a diaphragm wall. A ring of smaller shafts are dug and filled with concrete to form a circular wall. Then the centre of the ring can be excavated with the retaining wall already in place.

I'm pretty sure they do. I mean after all you often have a ramp in to it anyhow, but I think they also use vertical shafts where they e.g. build a subway station anyways.

How do they steer? By using perfectly machined custom segments that turn them in the correct direction?

They touch on that briefly at 8:10 in the video. The rings aren't perfect cylinders; the top and bottom are angled so that each ring is slightly longer on one side. (I.e. They resemble radial slices of a torus.) If each ring is rotated 180 degrees relative to its neighbors, the lengths average out and the tunnel goes straight. If the orientation is kept roughly constant, the tunnel curves in the direction of the short side of the cylinders.

This is partially correct. This is how the curve is maintained with the concrete liner. Steering is also accomplished via articulation jacks at the head and controlling differential stroke of the main jacks.

It should be noted that only certain types of precast segments work the way that is stated with all rings having an angled face - other types have specific concrete segments for each particular curve with the rest of the rings being planar. This approach has gone away in the industry with advances in software.

Does the machine itself deform while going through a curve?

Technically the answer is yes (any stress state results in deformation) but for all practical purposes the answer is no. The TBM does not bend to any degree worth talking about and is considered rigid.

This leads to curves in tunnels generally having a very large radius because you have to build the leading part of the curve inside a rigid cylinder. The tunnel is slightly smaller than the TBM and so some curvature can be tolerated.

So I suppose the curvature is much smaller than what a typical train can tolerate.

This is how it worked before Elon Musk reinvented it by buying a sewer boring machine and running it dozens of feet under a desert.

I'm not sure if your comment is meant to be snarky. But seriously... What is Elon doing differently?

As I understand it (and I am certainly not qualified in any regard with respect to this type of engineering) he is aiming to increase velocity by decreasing diameter (ie couple meter diameter vs 10m diameter) and then also looking at how they can ‘juice’ the machine using engineering magic

And I'm just going off of Wikipedia here on the Boring Company's page but apparently they modified a commercial borer to be 3x as fast as the original and are currently trying to manufacture a borer of their own design which they claim will be 10x faster.

The Boring Company took 2 years to go 6000 ft at 15’ diameter excavated.

There are plenty of ways to slice and dice this number up but the short version is that this is not faster than how the original TBM performed (let alone 3x) - I know the guys that Elon bought the TBM from and the guys that those guys bought it from.

As I’ve said in previous posts about this, TBM operation is not the limiting factor in building a tunnel. Permit acquisition and third parties are the longest part of tunneling projects by far.

The London Tube was built with a 3.58m diameter. Jubilee Line Extension had a 4.4m diameter, Crossrail will have 6.2m diameter. So the diameter reduction is not that much smaller, and it certainly isn’t the smallest attempted.

The original Tube tunnels actually have several problems - the tight diameter means that air conditioning is basically an impossibility (no room for the equipment in vehicles and nowhere to output the heat), and it makes maintenance and emergency evacuation annoying and hazardous if you can’t have a walkway for people to walk alongside the trackway.

most of the original tunneling was done by hand, so i'm not sure if it's directly comparable. There was an interesting article regarding the heat transfer to the surrounding ground recently - [0] that i'm sure you'll find interesting if you haven't seen it before!

Jubilee Line Extension was the '90s and Crossrail is opening soon, so those definitely weren't by hand!

I have seen articles about it, as well as a recent proposal to use that heat for heating homes. But it just illustrates the (many) potential pitfalls of small diameter tunnels, because you really don't want your tunnel to become an oven after a few decades of heat generated from braking.

Other pitfalls include:

You need space for adequate ventilation. This is less of a problem with electric propulsion, but you do still need it for emergencies (like a fire). And then there's the issue of noise; if your vehicle is too small compared to the tunnel, then the air being forced out once you get to a larger space (like the outside or a station) creates loud noise. Japanese high speed rail trains have much stranger aerodynamic shapes than European ones because they built smaller diameter tunnels and this ended up causing noise issues at higher speeds.

Making promises he can't keep about things he doesn't properly understand to convince well-meaning but ultimately naive investors to keep coughing up the dough, as usual.

Trying to do something isn't a promise.

No, saying "Boring company will transport your car all the way into your garage" is a promise. Saying "The Boring Company will be using dirt from tunnel digging to create bricks for low cost housing" is a promise. So is "Just received verbal govt approval for The Boring Company to build an underground NY-Phil-Balt-DC Hyperloop Hyperloop. NY-DC in 29 mins."

Elon Musk has a practically unbroken track record of making wildly speculative, overconfident promises about all sorts of technologies that never materialise, and gullible people lap it up like it's going out of fashion. People are dying because of Tesla's irresponsible and misleading marketing, and Musk shouldn't get a pass just because some people think he's a visionary.

I think most people understand that when he says those things, he's stating ambitions rather than "making promises."

Tell that to the families mourning the deaths of the people who didn't realise something called AutoPilot and dishonestly marketed as FSD capable is just an ambition.

It's hard to give a non-snarky answer because The Boring Company has been very light on actual details, as most of their publicity has focused on the alternative transit method they propose instead of TBM details. Even most of the details on tunneling they suggest aren't meaningful for making it faster; the only one that really is making TBMs run 24/7.

The only reason Elon thinks he can make it faster that I can divine is engineering magic.

To be fair, people said this about Tesla and SpaceX as well.

Given his track record, I'm inclined to believe he understands the problem space and how to solve it better than you or I.

Yes, the burden is on him to execute, but that will take him years. The argument that "I don't understand it therefore it's invalid" holds little meaning. Musk isn't a person who gets this deep into a project without a high likelihood of success, historically.

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