
How Tunnel Boring Works (2011) [video] - rkagerer
https://www.youtube.com/watch?v=qx_EjMlLgqY
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Jerry2
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](https://www.youtube.com/watch?v=qlrZ3G0tAzY)

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

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BigJono
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?

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abduhl
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.

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

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rkagerer
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...](https://www.herrenknecht.com/en/products/productdetail/85/?wvideo=y66srmx0vz)

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

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ekianjo
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?

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7952
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.

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

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jetrink
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.

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abduhl
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.

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amelius
Does the machine itself deform while going through a curve?

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abduhl
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.

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

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new_realist
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.

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

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robbiep
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

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bobthepanda
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.

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robbiep
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!

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bobthepanda
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.

