November 19, 2018 • 37 mins
How do tunneling machines work? We look at the science and tech behind burrowing under the Earth.
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Speaker 1 (00:04):
Get in touch with technology with tech Stuff from half
stuff works dot com. He there, and welcome to tech Stuff.
I'm your host, executive producer, Jonathan Strickland, and I love
all things tech. And in past episodes of tech Stuff,
I have covered stuff like the history of subway systems,
(00:26):
and I've given an overview of the Boring Company that's
one of Elon Musk's companies and its mission to create
underground tunnel systems beneath cities to allow for a new
method of getting around town and also methods for getting
between towns. So you've got the loop and the hyper
loop concepts. But today I'm going to talk more about
(00:48):
the enormous machines used to dig out tunnels as well
as the smaller ones that are used to dig out
smaller tunnels, the ones that are used for utility lines,
or the ones that are really huge to make transportation tunnels.
Those are gigantic, they're incredibly interesting, and they consist of
multiple machines joined together to make a comprehensive tunneler. So
(01:09):
this is a this is a big topic, both figuratively
and literally. So first, let's talk about the challenges that
we face if we want to dig a tunnel, specifically
a tunnel under a populated area like a city. So
we have to make sure that the method we use
will not create structural problems for the region above. Right,
we don't want any collapses. The tunnel can't create any
(01:31):
welling or sink holes. Uh if it cannot undermine buildings.
The method we use has to preserve the stability of
everything else above it, or catastrophe will occur. Obviously, Likewise,
the method we use needs to protect the tunnel that
we're digging. We have to create a way to prevent
(01:52):
the tunnel from collapsing in on itself. Through stone, maybe
this requires a little bit of work just to force everything,
but through soft earth you have to come up with
something else. So there's got to be a mechanism to
improve the structural stability of a tunnel. The machine we
build has to be able to cut through lots of
different kinds of ground, from sandy soft material to rocky surfaces,
(02:17):
or dry material to wet mud. So the cutting edge
of the tunnel er has to be capable of handling
all of that, or you need to be able to
swap out cutting edges depending upon the kind of ground
you're going through, and that's easier said than done. Typically
you just want to keep the same cutting edge on
(02:38):
your your tunnel, or for the entirety of a dig
you may have to replace little components on it, but
that's a lot easier in the grand scheme of things
than replacing an entire cutting head. We'll get more into
that in a bit. We also have to have a
way to remove all the material we're cutting or digging through.
The excavated material, which is often called muck or spoil.
(03:02):
All of that stuff has to go somewhere, so whatever
method we use needs to take that into account so
that we can manage all that mess as we keep digging.
The digging mechanism needs a method for transporting the muck
or spoil out from behind the cutting head and preferably
out of the tunnel itself. So modern tunneling machines do
(03:23):
these things in really interesting ways. There are differences between
the various machines. They generally are doing the same thing,
but they do it in different ways. Some are almost
completely automated, others have a balance between human controlled systems
and automated systems. The Boring Company posted a video that
showed a machine apparently following the input of someone holding
(03:46):
an Xbox game controllers. So that was interesting. Now, I
don't know if that machine was actually following the directions
of the person with the controller or the whole thing
was an orchestrated video. It seemed to correspond with the
person holding the controller, although that could have been a
very well rehearsed routine and the person with the controller
(04:09):
is just pushing the controls in different directions and hitting
different buttons in time with something that has already been programmed.
That's a possibility. I suppose there's no reason someone couldn't
make an interface between a game controller and a huge machine.
But then, considering the precision needed for some of the
operations we're going to talk about, it does make me
(04:30):
a little skeptical. I mean, it's possible that the video
is completely legitimate, but I'm a bit concerned about the
work the machine would be doing in that case, because
I play Xbox a lot and precision is not one
of the words I would use to describe the control system.
But maybe I'm wrong. It's entirely possible. Now, Ideally, the
device we create should be able to cut through the ground,
(04:55):
shore up a tunnel as it does so so that
the tunnel remains stable, move the spoil or muck from
the dig so it's out of the way, and do
so without disrupting anything above the ground. So how the
heck is that possible? Well, first, the type of tunneling
machines we use to drill the way for stuff like
utility lines to subway trains or tunnels come in a
(05:18):
range of sizes. Some are relatively small, and they're meant
for digging tunnels that will house cables or utility lines.
The company Robbins produces small tunneling machines that range from
two feet or about sixty one centimeters up to six
ft or one point eight meters in diameter. They make
(05:39):
bigger ones too, but these are the ones that they consider,
these small boring machines from two to six feet in diameter,
and these machines actually rely upon another device. It's called
an augur boring machine, which provides two things. It provides
the rotational force that is used to turn the cutting head,
(06:00):
which is the part of the tunneler that actually makes
contact with the earth, and it also provides the forward
thrust to push that cutting head against the earth, so
that it is continuously making that contact and cutting away.
The cutting face or the cutting head and the end
of the augur can interlock with each other sort of
(06:22):
like a socket wrench, and it's detachable sockets. So you've
got the end of this auger blade coming in all
the aug boring machine that connects it its sockets into
the actual cutting head, and that's where you can transfer
the rotational force from the auger boring machine to the
cutting head, which spins like a disc on the other
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end of the scale. So that's the small side. If
you want to talk big, let's go with the biggest
there ever was, at least up to now. You've got
something like Bertha. Bertha was the largest boring machine ever
made so far. Anyway, the cutting face, that is the
front of the cutting head, measured fifties seven feet in diameter,
(07:09):
that's seventeen point four meters. The machines length from the
face of the cutting head all the way to the
back of the machine was three hundred twenty six ft
or nine nine meters. While a small boring machine is
an extension of an auger and it gets its rotational
power and its forward thrust from this auger boring machine.
(07:32):
Bertha was like a giant tunneling facility. It had a
frame mounted behind the cutting head that housed stuff like
break rooms and an operator office. So you had people
walking inside this giant machine that had a shielded part
in the front where the cutting head was, and then
the part in the back was. It looked like a big,
(07:55):
open scaffolded machine with lots of conveyor belts and these
little rooms for for operator rooms and break rooms that
kind of stuff. So the cutting head looks like a
big disc with teeth sticking out of the face of it,
and then behind that you've got this big cylinder. The shield.
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The shield is what protects the cutting head and the
immediate part of the tunnel or from behind the cutting
head and keeps the earth stable behind it, so it's uh,
it's keeping everything from caving in essentially. Behind that, you've
got an enormous um crane. More on that in a bit,
(08:39):
and you also have a screw conveyor. A screw conveyor
is kind of like an auger. It's got this helical
screw that's designed to lift spoil or muck up to
a conveyor belt. The conveyor belt sends all that muck
back through the back of the machine and eventually completely
out of the tunnel. All of these elements are mounted
within this enormous metal for aim that's part of the
(09:00):
tunneling machine. It's typically held into place by hydraulic legs
that brace against the sides of the tunnel to keep
it steady. The frame or maybe wheels as well. It
could be wheels that are are locked into place. They
have very powerful breaks and they just locked into place
on the sides of these tunnels. Bertha was a special
type of borer called an earth pressure balanced tunneling boring
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machine or EPB. I'll explain more about that and a
little bit. So let's start with the small boring machines.
A lot of the principles behind the small boring machines
apply to the larger ones. That's just they're much bigger scale.
So the drive for those smaller machines, as I mentioned,
was an auger boring machine. Now, an auger is a
(09:44):
tool that's a type of drill. Usually it has a
helical bit, meaning the bit is in the shape of
a helix, and the helical bit acts like a screw
conveyor and It works on the same principle as an
ancient piece of technology called Archimedes screw. And your typical
Archimedes screw has a helical bit housed inside a pipe,
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and you don't have a whole lot of space between
the screw and the pipe, so the screw is very
snug inside this pipe. You can rotate it, but that's
all you know. It's it's otherwise almost essentially making contact
with the sides. It's very important for this. You set
the screw at a forty five degree angle with the
lower section immersed in water. So imagine you have a
(10:28):
low body of water. You insert and Archimedes screw at
this forty five degree angle into the water, and then
when you turn the screw, it will lift or pump
water out of the low end. As the water moves
up the screw, it acts like a rotating ramp and
it pushes the water up traps the water lifts it
up to a higher elevation, so you can actually transfer
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water from a low area to a high area using this.
You can build one of these yourself with a dowel
and some plastic tubing and you just wrap the plastic
two being around the dowel and a spiral, and when
you put the dowel into water and you keep the
dowel at like a forty five degree angle, as long
as you're turning the dowel in the proper direction, it
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will continue to dip into the water, and that water
will slowly make its way all the way up the
coil as you rotate the dowel. Augers are used for
all sorts of things. So wood drill bits typically have
those helical grooves in them, and this helps convey shavings
out of the hole that you're drilling and gets that
those wood shavings out of the way so they don't
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just gum up the space. And you can use an
auger to drill holes into the earth. The tunneling machines
i'm talking about used augers for their rotational force and
their ability to transport spoil out of a tunnel. The
actual cutting head of these tunneling machines wasn't on the
augur itself. It was a separate piece and it does
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the actual tunneling part. The auger boring machines sold by
companies like Robin are large devices that allow for horizontal
boring and they look like these big metal rectangular construction devices,
and out of one end parallel to the ground is
the auger blade. So to use one, first thing you
(12:16):
would do is you would dig a pit down to
whatever level you need so that where the tunnel is
going to be. So you're gonna actually have to dig
a pretty long and deep rectangular pit and get it
down to the level where you're gonna dig this tunnel.
And then you would put down tracks which the auger
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boring machine would sit on, and probably a concrete barrier
at the back to act as a surface that the
auger boring machine can thrust off of to start with.
And that's your basic point of operations for the beginning
of your tunneling process. The machine will provide the torque
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necessary for everything to work, and torque is a twisting
force that tends to cause rotation. When you use a screwdriver,
you are applying torque to a screw. With augur boring machines,
torque comes from the rotational force created by the motor
driving the auger And I've talked a lot about motors
in previous episodes of Tech Stuff, So rather than go
(13:24):
on through all that again, we'll just say it's a
motor that creates the rotational force. The international systems of
unit metric for torque is the Newton meter and Augur
boring machine on the more modest side, might produce a
peak torque of about four hundred newton meters or two
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foot pounds of force. I've got a lot more to
say about these tunneling machines, but first let's take a
quick break to thank our sponsor the honors. Rotational force
transfers to the cutting head of this boring machine. These
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components make contact with what's called the cutting face of
the dig that's the part of the earth or rock
that the cutting head is actually making contact with. The
cutting head is the surface that goes against the rocks, boulders,
and sand. So this cutting surface can have numerous tools
on it, including cutting disks which are used mostly to
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break up rocks and boulders, scrapers and other projections meant
to remove material to excavate it, to break it up,
excavate it and move it back into the back part
of this tunneling machine. They also typically have gaps in
the face of the cutting head that allows this spoil
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to pass through the cutting head and move back through
the chain. Uh the spoil is able to come through
that way, it encounters the auger blade that acts like
a conveyor screw, and the auger blade will pull the
spoil or muck away from the cutting surface. Now, not
all cutting tools are suitable for all types of ground. Some,
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like the cutting disks, like I said, are really good
for breaking up larger rocks and boulders into smaller pieces.
But if you're encountering a lot of mud or water
in this tunneling job, a different selection might be needed
in order to dig the tunnel and to convey the
material to the conveyor screw and maintain the cutting faces stability.
Wet ground presents challenges in that regard. I'll talk more
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about that in a bit. So the cutting tools tend
to be made from really really hard materials because you
want them to last a good long while, preferably for
the length of the tunneling job. So you might use
something like tungsten carbide, and it's also sometimes just called
carbide for short. And this is a pretty cool material.
(15:53):
So tungsten is more than twice as dense as steel.
The process for making tungsten carbide involves lots of steps,
but essentially you're taking ore that contains tungsten, so something
like wolf from right. Uh. So you take wolf from
right and you crush it. You maybe you treat it
with some chemicals, You heat it up, and you end
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up with something like tungsten oxide. Then you treat it
in a carbonizing process, such as heating it to more
than twelve degrees celsius. This removes the oxygen from that
mixture and it binds carbon to the tungsten. Then you
sort out the grains of tungsten carbide into piles based
on grain size. You typically would use something like a
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sieve to do this. So you pass through sieves and
you get the finest grains out, and then you go
with progressively larger sieves to get the other grains. You
mix that with some other materials, including cobalt. Cobalt connect
as a binding agent. You press the mixture into a
mold high temperature mold for the whatever tool you're building.
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Then you put it into what was called a centering furnace,
which is hot enough to melt the cobalt, which then
binds everything together kind of like the force. Then you
remove the tungsten carbide you and uh then hone it
down to its final size and its final shape. And
I've skipped a lot of details here. Anyone who has
worked with tungsten carbide, who's made the stuff knows that.
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But this is a very high level kind of look
at the process. And in the end, what you have
is a tool much stronger than steel that can stand
up to a lot of wear and tear, which is
perfect for cutting into stuff like stone and breaking up rocks.
So the business end of the boring machine is the
cutting head, and that's typically protected by some shielding that
that sort of cylinder that's from the point of the
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cutting face and extends back quite a bit. And then
sometimes you might use a length of pipe right behind that,
especially if you're using cutting these utility size holes, then
you would have metal pipe that would be connected to
the cutting head and surrounding the auger blade. On the
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really big machines, it's typically part of the boring machine itself.
You don't just have a cutting head that's extending from
a pipe. It's all part of the same machine. This
big shield that will extend back several feet. The shielding
keeps the area near the face stable and it makes
direct contact with the earth that you're cutting through, So
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it's it's sort of the tip of the tunneling machine.
So the cutting surface of the toweling machine presses against
the cutting face and turns it up to start digging horizontally.
The pressure is generated by these in the small ones
by the boring machine. It has those tracks I talked
about that's laid down in the pit and it starts
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to roll forward, and the rolling forward is what puts
the forward thrust against the the cutting head which makes
contact with the the earth it starts to cut through
and tunnel in. This is a very slow process. It
is not happen quickly at all. So when I say
roll forward, I really just mean putting forward pressure, forward
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thrust on that cutting head. Uh. The process itself takes
quite a long time, and the auger is typically wheeled
and has some sort of bracing technology to hold it
into place so that it doesn't just push itself backward
while it's trying to cut through this tunnel. Between the
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auger boring machine and the tunneler that you've you're using,
you would lay down this metal pipe that contains the
auger blade and it would attach to either end right,
So one end of the auger blade attaches to the
cutting head, the other end of the auger blade attaches
to the auger boring machine. And then the auger boring
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machine starts to turn, the auger blade turning, the cutting
head starts to tunnel into the earth. But obviously this
only allows you to tunnel so far right. Eventually you're
going to push the auger boring machine up against the
point where the tunnel opens up. So what happens then?
How do you go any further? If you're digging a
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short tunnel, obviously it's not a problem. But if it's
a long tunnel, what do you do? Well, what you
would do is you would stop the auger boring machine.
You would you would stop your tunneling process. This is
the cutting phase. You'd stop the cutting phase, and you
would detach the auger boring machine from the blade and
the pipe that it was pushing into the tunnel. You
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would pull the auger boring machine back to its starting position.
You would then lower into the digging pit a new
length of pipe inside, which is another length of auger blade,
and then you would connect the two lengths of auger
blade together the one that's already in the tunnel and
the new length of auger blade that you've just lowered
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into the pit. You would connect the other side to
the auger boring machine, and now you've essentially doubled the
length of your auger blade and you can start up again.
A full dig job might require you do this several times,
and essentially you would keep doing it until the dig
job was done. Uh, if the dig job was super long,
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this is problematic because eventually you're going to get to
a length where the auger boring machine is not going
to be able to generate the torque necessary to turn
that long of a blade and the cutting head. But
generally speaking, that's how it works. You just keep on
lowering extensions into the pit, connecting it to the part
that's already been pushed into the tunnel, and start up again.
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It's actually kind of neat. There are a lot of
videos on YouTube that show this process. I watched tons
of them because it was I don't know, I was
turned into like a little kid again watching construction videos. Now,
for the larger boring machines, the really big ones that
are digging tunnels for like, you know, cars, or trains
or whatever. There's a really cool method for building out
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a tunnel. These machines are way too big to draw
thrust or rotational power from an auger boring machine. You
would not have just a truly enormous auger boring machine
outside in a deep pit. So instead they have all
the mechanical elements incorporated into this enormous tunneler, and there's
so many moving parts that it's hard to keep track
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of them all. They have their own rotational motor to
generate that incredible torque needed to turn the cutting heads that,
like I said, can be meters in diameter. Bertha was
seventeen nearly seventeen and a half meters in diameter. You
need a really powerful motor to be able to turn
that with the force necessary for it to start cutting
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through the earth. Behind the cutting head, typically you have
a chamber. There are a couple of different major types
of tunneling machines, so these chambers can serve slightly different purposes,
And I guess I should go ahead and break them
down because it all has to do with the type
of material your dig through. If it's pretty much solid
rock you're digging through, you could use what's called an
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open tunnel boring machine. These do not have the protective
shielding cylinder that extends back from the cutting head. They're
just open because they're cutting through essentially stone, and they
the rest of the machine is just straight behind it,
unprotected for the most part, and the machine would use
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hydraulic grippers to brace against the walls of the tunnel
it was building and to provide the forward thrust needed
for it to make contact with the cutting face to
keep on cutting crews behind it would add support systems
to the tunnel like rock bolts and wire mesh, and
that would help support the tunnel as it was being dug.
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But otherwise you don't have to have any additional stuff.
You know, you you have like a conveyor to move
the spoil away from the cutting head and down the tunnel,
but otherwise eyes you don't need all the other bits
and pieces. For soft ground, however, you might need something
like an earth pressure balance machine. These machines have a
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shield to keep the tunnel supported around the end of
the boring machine. So this is that cylinder I was
talking about that extends back from the cutting head. They
hold up the tunnel from uh that that's made immediately
behind the cutting head, otherwise it would just collapse in
on itself. Behind the cutting head, there's a chamber and
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that's where the muck or spoil comes into the tunneler.
There's a screw conveyor that then can take that stuff
out of this chamber, and the screw conveyor can turn
at different speeds, and the reason why you would want
to alter the speed of the conveyor is to control
the amount of pressure inside that chamber. The pressure can
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help keep the cutting face stable. So if you need
more pressure to keep the cutting face stable, maybe there's
water that would otherwise come into the system, then the
screw conveyor can slow down. It can remove material more
slowly from the chamber, and it creates more pressure so
that the tunnel doesn't just flood and collapse in on itself.
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If less pressure is needed, the screw conveyor can speed
up and remove more material from the chamber and that
decreases the pressure behind the cutting head. There's another soft
ground tunneling machine type called a slurry shield, which is
for ground that has really high water pressure inside it,
or is made up of very granular particles like sand
or gravel or some types of clay. And with these
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boring machines you create a pressurized slurry. You use a
material called bentonite clay and you suspend it in water
and this helps create the hydrostatic pressure needed to keep
the cutting face stable during tunneling, and it also acts
as away to transport muck back away in the cutting head.
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In this case, the muck ends up being almost liquid
or gelatinous in nature, so this mixture can be injected
into the cutting face through pressurized nozzles. It's like it's
like you're squirting out this bentnite stuff in front of
the tunneler and this creates a sort of membrane that
protects against the exterior water pressure and it keeps water
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from rushing into the tunneling machine. The excavated material and
slurry mixture can be pumped back out of the tunnel.
Instead of using a screw conveyor, you're actually using pipes
and pumps to pump it out the back. Then you
can process it, and some of that material you might
even use in construction, so you might reclaim some of that,
not just dump it as spoil. Now next I'm gonna
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explain how these large tunneling machines could keep digging underground
even in soft earth, and how they build the solid
tunnel behind them. But first let's take another quick break
to thank our sponsor. So in these soft earth tunneling machines,
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there's an apparatus that is just inside the shielded section
near the cutting head, so it's protected by that cylinder
I was talking about. This device is an erector. It
puts up rings of concrete in segments uh there. The
segments can be several meters in length. That all depends
upon the diameter of the tunnel you're digging. So what
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the erector does is there's a conveyor that will pull
prefabricated segments of concrete rings to the erector. The erector
comes down, picks up each segment and then places them
as part of the tunnel wall. So it does this
piece by piece, and it ends with a wedge shape
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piece called the keystone. The segments of concrete ring essentially
snapped together. They use things like dowels and holes to
snap together, and they also are bolted together. And the
concrete ring acts as a tunnel interior. And it's also
while the tunneling machine uses to push off of to
use as thrust when tunneling. So the small borders I
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talked about earlier do this in too processes two stages really,
so do the large ones. So first, let's say that
you've been tunneling for a while, right, You've set up
several meters of tunnel, so the process has been going
on for a few days. Hydraulic arms on the tunneling
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machine press against the edge, the outer edge of the ring,
the one that's furthest inside the tunnel. So it's as
far as you've gone, and in constructing this tunnel, this
is still under the protective shielding of that cylinder I
was talking about. So you have these hydraulic arms that
are pressing on that outer edge. Those hydraulic arms exert
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pressure and create force to put the cutting head against
the cutting face. So they as they extend, they're at
their creating that forward thrust for the cutting head, so
it's actually pushing the cutting head against the earth. Now,
this tends to go really really slowly, and once all
those hydraulic arms have extended all the way, they can't
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go any further. That means you're not going to get
any more forward thrust, the tunneling phase ends and the
erector moves into place, and now we move into the
second phase, the building phase. So for each segment of ring,
the respective hydraulic arms that are pushing against that outer
edge will withdraw, and that gives the erector the enough
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room to snap the next ring section into place. Once
it has done that, the hydraulic arms can extend again
and brace against this new section of ring. And once
you've completed a whole ring segment, you've extended the tunnel
by one more ring. Now each ring might be you know,
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a meter or so in with so you've just extended it.
Then the next tunneling phase can begin. All the hydraulic
arms are now closer in their one ring segment further contracted,
so they can start extending again and they can create
thrust again. And so you do this in this sort
of seesaw approach. You tunnel, you stop, you build, the
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building creates the space you need in order to create
the thrust, and you tunnel again. It's actually pretty interesting,
and there's a lot of videos that show this. I
know it's kind of hard to envision from audio, but
I highly recommend if you want to check this out,
you can look for tunneling machine videos to see the
process I'm talking about. So what happens though if you
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need to turn as you're tunneling, Because what I've been
describing works really well if you're going in a straight line.
But if you're in one of these big machines and
you need to make that tunnel curve a bit, well,
for those sections, you might use ring segments that are conical,
which means that by changing the direction of this cone
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shape you can create a curve. And plus you have
these hydraulic arms behind the cutting head that can exert
different levels of thrust and turn the direction of the
cut just slightly so like the left side is pushing
out a little further than the right side. That starts
to create the curve that you need in order to
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meet whatever the shape of the tunnel needs to be.
Over time, this creates these really long curves. Now, these
machines do not go very fast. The cutting head might
only turn two or three times per minute, and according
to the Boring Company, your average snail is a speed
demon compared to a tunnel boring machine can move fourteen
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times faster than a tunneling machine as it travels a
straight line, and tunneling also is really expensive and again
according to the boring Company, a mile of tunnel could
cost up to one billion dollars depending upon the project.
These are really big obstacles that stand in the way
of building out tunnel systems to allow for underground travel
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in some of the busiest cities in the world. So
the boring Company hopes to bring both the time it
takes to complete a project down and the cost down.
To increase speed, the Boring Company is increasing the cutting
speed of the cutting head, so they're increasing the number
of rotations it does per minute. This also requires building
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out other systems like cooling systems to help keep the
bearings and other components at the right nominal operating temperatures.
The company is also developing machines that will not have
to alternate between digging and the building phases, so that
they can just keep cutting continuously. They don't have to
cut stop, build a segment of ring, cut stop, build
(32:58):
a segment of ring. The company also proposes using the
excavated earth when possible, to make bricks, which might then
be used to line the tunnel itself, which would cut
down the need for making concrete, and that's environmentally a
good thing because concrete production causes a lot of pollution.
Nearly five percent of the world's greenhouse gas emissions comes
(33:19):
from concrete production. In early November two eighteen, Elon Musk
tweeted out a video of the Hawthorne Test tunnel. That's
a route that leads from SpaceX Is parking lot and
moves under street near Los Angeles for about two miles.
And the tunnel is supposed to open on December tenth,
(33:40):
two eighteen, and they're supposed to be a big opening
celebration event that day and on the following day, the
boring company will offer free rides to the public in
the tunnel, which sounds pretty exciting. Meanwhile, these sorts of
tunneling machines are being used all over the world to
dig out subway systems. The tunnel Bertha Ug in Seattle
(34:01):
is a replacement for the Alaskan Way Viaduct that's an
elevated highway in Seattle, so instead of building up, they're
building down. The project was originally supposed to take two
and a half years to complete. Instead it took nearly
four years due to various setbacks, one of which happened
early early on in the progress project when um they
(34:21):
encountered a steel rod that was underground. And UM they've
also had a few attempts by various Washington politicians to
kill the whole project. They were saying that it was
um an embarrassment, it was a waste. But it kept
on going and it did complete. The tunneling process ended
in April. The tunnel as of the recording of this
(34:44):
podcast isn't open yet. It's not scheduled for use until
February twenty nineteen. But once Bertha finished the digging process,
it broke through into what was called a disassembly pit,
where it was well, just a bold Bertha would not
be used to dig any more tunnels. Instead, anything that
could be melted down and recycled was and everything else
(35:07):
was kind of, you know, thrown away. The massive machine
was cut up into twenty ton pieces, but since the
machine weighed seven thousand two tons, that took a long time.
Since tunneling ended, engineers have been building a double deck
highway inside the tunnel that Bertha dug. And that's all
(35:28):
I have to say about these tunneling machines. They are
really interesting. Uh. The more I looked into them, the
more I was fascinated by how enormous the big ones
are and the fact that it's a machine that also
is like a construction site all by itself is pretty phenomenal.
And just seeing how simple things like the Archimedes screw
(35:49):
could be incorporated into these machines to move massive amounts
of earth. It also speaks to the ingenuity of the
ancient designers like Archimedes who came up with these ideas
that we're still finding uses for today, These these simple
machines that are still the best way to do certain things.
I think it's pretty interesting and I really look forward
(36:09):
to finding out how Elon Musk's boring company is able
to advance the technology. And maybe pretty soon we'll have
underground tunnels in all major cities that make getting around
much much easier. I would look forward to that too.
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should cover in tech Stuff, why not visit our website.
(36:31):
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(37:37):
and thousands of other topics. Because it how staff works
dot Com
Get in touch with technology with tech Stuff from half
stuff works dot com. He there, and welcome to tech Stuff.
I'm your host, executive producer, Jonathan Strickland, and I love
all things tech. And in past episodes of tech Stuff,
I have covered stuff like the history of subway systems,
(00:26):
and I've given an overview of the Boring Company that's
one of Elon Musk's companies and its mission to create
underground tunnel systems beneath cities to allow for a new
method of getting around town and also methods for getting
between towns. So you've got the loop and the hyper
loop concepts. But today I'm going to talk more about
(00:48):
the enormous machines used to dig out tunnels as well
as the smaller ones that are used to dig out
smaller tunnels, the ones that are used for utility lines,
or the ones that are really huge to make transportation tunnels.
Those are gigantic, they're incredibly interesting, and they consist of
multiple machines joined together to make a comprehensive tunneler. So
(01:09):
this is a this is a big topic, both figuratively
and literally. So first, let's talk about the challenges that
we face if we want to dig a tunnel, specifically
a tunnel under a populated area like a city. So
we have to make sure that the method we use
will not create structural problems for the region above. Right,
we don't want any collapses. The tunnel can't create any
(01:31):
welling or sink holes. Uh if it cannot undermine buildings.
The method we use has to preserve the stability of
everything else above it, or catastrophe will occur. Obviously, Likewise,
the method we use needs to protect the tunnel that
we're digging. We have to create a way to prevent
(01:52):
the tunnel from collapsing in on itself. Through stone, maybe
this requires a little bit of work just to force everything,
but through soft earth you have to come up with
something else. So there's got to be a mechanism to
improve the structural stability of a tunnel. The machine we
build has to be able to cut through lots of
different kinds of ground, from sandy soft material to rocky surfaces,
(02:17):
or dry material to wet mud. So the cutting edge
of the tunnel er has to be capable of handling
all of that, or you need to be able to
swap out cutting edges depending upon the kind of ground
you're going through, and that's easier said than done. Typically
you just want to keep the same cutting edge on
(02:38):
your your tunnel, or for the entirety of a dig
you may have to replace little components on it, but
that's a lot easier in the grand scheme of things
than replacing an entire cutting head. We'll get more into
that in a bit. We also have to have a
way to remove all the material we're cutting or digging through.
The excavated material, which is often called muck or spoil.
(03:02):
All of that stuff has to go somewhere, so whatever
method we use needs to take that into account so
that we can manage all that mess as we keep digging.
The digging mechanism needs a method for transporting the muck
or spoil out from behind the cutting head and preferably
out of the tunnel itself. So modern tunneling machines do
(03:23):
these things in really interesting ways. There are differences between
the various machines. They generally are doing the same thing,
but they do it in different ways. Some are almost
completely automated, others have a balance between human controlled systems
and automated systems. The Boring Company posted a video that
showed a machine apparently following the input of someone holding
(03:46):
an Xbox game controllers. So that was interesting. Now, I
don't know if that machine was actually following the directions
of the person with the controller or the whole thing
was an orchestrated video. It seemed to correspond with the
person holding the controller, although that could have been a
very well rehearsed routine and the person with the controller
(04:09):
is just pushing the controls in different directions and hitting
different buttons in time with something that has already been programmed.
That's a possibility. I suppose there's no reason someone couldn't
make an interface between a game controller and a huge machine.
But then, considering the precision needed for some of the
operations we're going to talk about, it does make me
(04:30):
a little skeptical. I mean, it's possible that the video
is completely legitimate, but I'm a bit concerned about the
work the machine would be doing in that case, because
I play Xbox a lot and precision is not one
of the words I would use to describe the control system.
But maybe I'm wrong. It's entirely possible. Now, Ideally, the
device we create should be able to cut through the ground,
(04:55):
shore up a tunnel as it does so so that
the tunnel remains stable, move the spoil or muck from
the dig so it's out of the way, and do
so without disrupting anything above the ground. So how the
heck is that possible? Well, first, the type of tunneling
machines we use to drill the way for stuff like
utility lines to subway trains or tunnels come in a
(05:18):
range of sizes. Some are relatively small, and they're meant
for digging tunnels that will house cables or utility lines.
The company Robbins produces small tunneling machines that range from
two feet or about sixty one centimeters up to six
ft or one point eight meters in diameter. They make
(05:39):
bigger ones too, but these are the ones that they consider,
these small boring machines from two to six feet in diameter,
and these machines actually rely upon another device. It's called
an augur boring machine, which provides two things. It provides
the rotational force that is used to turn the cutting head,
(06:00):
which is the part of the tunneler that actually makes
contact with the earth, and it also provides the forward
thrust to push that cutting head against the earth, so
that it is continuously making that contact and cutting away.
The cutting face or the cutting head and the end
of the augur can interlock with each other sort of
(06:22):
like a socket wrench, and it's detachable sockets. So you've
got the end of this auger blade coming in all
the aug boring machine that connects it its sockets into
the actual cutting head, and that's where you can transfer
the rotational force from the auger boring machine to the
cutting head, which spins like a disc on the other
(06:45):
end of the scale. So that's the small side. If
you want to talk big, let's go with the biggest
there ever was, at least up to now. You've got
something like Bertha. Bertha was the largest boring machine ever
made so far. Anyway, the cutting face, that is the
front of the cutting head, measured fifties seven feet in diameter,
(07:09):
that's seventeen point four meters. The machines length from the
face of the cutting head all the way to the
back of the machine was three hundred twenty six ft
or nine nine meters. While a small boring machine is
an extension of an auger and it gets its rotational
power and its forward thrust from this auger boring machine.
(07:32):
Bertha was like a giant tunneling facility. It had a
frame mounted behind the cutting head that housed stuff like
break rooms and an operator office. So you had people
walking inside this giant machine that had a shielded part
in the front where the cutting head was, and then
the part in the back was. It looked like a big,
(07:55):
open scaffolded machine with lots of conveyor belts and these
little rooms for for operator rooms and break rooms that
kind of stuff. So the cutting head looks like a
big disc with teeth sticking out of the face of it,
and then behind that you've got this big cylinder. The shield.
(08:17):
The shield is what protects the cutting head and the
immediate part of the tunnel or from behind the cutting
head and keeps the earth stable behind it, so it's uh,
it's keeping everything from caving in essentially. Behind that, you've
got an enormous um crane. More on that in a bit,
(08:39):
and you also have a screw conveyor. A screw conveyor
is kind of like an auger. It's got this helical
screw that's designed to lift spoil or muck up to
a conveyor belt. The conveyor belt sends all that muck
back through the back of the machine and eventually completely
out of the tunnel. All of these elements are mounted
within this enormous metal for aim that's part of the
(09:00):
tunneling machine. It's typically held into place by hydraulic legs
that brace against the sides of the tunnel to keep
it steady. The frame or maybe wheels as well. It
could be wheels that are are locked into place. They
have very powerful breaks and they just locked into place
on the sides of these tunnels. Bertha was a special
type of borer called an earth pressure balanced tunneling boring
(09:23):
machine or EPB. I'll explain more about that and a
little bit. So let's start with the small boring machines.
A lot of the principles behind the small boring machines
apply to the larger ones. That's just they're much bigger scale.
So the drive for those smaller machines, as I mentioned,
was an auger boring machine. Now, an auger is a
(09:44):
tool that's a type of drill. Usually it has a
helical bit, meaning the bit is in the shape of
a helix, and the helical bit acts like a screw
conveyor and It works on the same principle as an
ancient piece of technology called Archimedes screw. And your typical
Archimedes screw has a helical bit housed inside a pipe,
(10:06):
and you don't have a whole lot of space between
the screw and the pipe, so the screw is very
snug inside this pipe. You can rotate it, but that's
all you know. It's it's otherwise almost essentially making contact
with the sides. It's very important for this. You set
the screw at a forty five degree angle with the
lower section immersed in water. So imagine you have a
(10:28):
low body of water. You insert and Archimedes screw at
this forty five degree angle into the water, and then
when you turn the screw, it will lift or pump
water out of the low end. As the water moves
up the screw, it acts like a rotating ramp and
it pushes the water up traps the water lifts it
up to a higher elevation, so you can actually transfer
(10:50):
water from a low area to a high area using this.
You can build one of these yourself with a dowel
and some plastic tubing and you just wrap the plastic
two being around the dowel and a spiral, and when
you put the dowel into water and you keep the
dowel at like a forty five degree angle, as long
as you're turning the dowel in the proper direction, it
(11:12):
will continue to dip into the water, and that water
will slowly make its way all the way up the
coil as you rotate the dowel. Augers are used for
all sorts of things. So wood drill bits typically have
those helical grooves in them, and this helps convey shavings
out of the hole that you're drilling and gets that
those wood shavings out of the way so they don't
(11:34):
just gum up the space. And you can use an
auger to drill holes into the earth. The tunneling machines
i'm talking about used augers for their rotational force and
their ability to transport spoil out of a tunnel. The
actual cutting head of these tunneling machines wasn't on the
augur itself. It was a separate piece and it does
(11:54):
the actual tunneling part. The auger boring machines sold by
companies like Robin are large devices that allow for horizontal
boring and they look like these big metal rectangular construction devices,
and out of one end parallel to the ground is
the auger blade. So to use one, first thing you
(12:16):
would do is you would dig a pit down to
whatever level you need so that where the tunnel is
going to be. So you're gonna actually have to dig
a pretty long and deep rectangular pit and get it
down to the level where you're gonna dig this tunnel.
And then you would put down tracks which the auger
(12:37):
boring machine would sit on, and probably a concrete barrier
at the back to act as a surface that the
auger boring machine can thrust off of to start with.
And that's your basic point of operations for the beginning
of your tunneling process. The machine will provide the torque
(13:03):
necessary for everything to work, and torque is a twisting
force that tends to cause rotation. When you use a screwdriver,
you are applying torque to a screw. With augur boring machines,
torque comes from the rotational force created by the motor
driving the auger And I've talked a lot about motors
in previous episodes of Tech Stuff, So rather than go
(13:24):
on through all that again, we'll just say it's a
motor that creates the rotational force. The international systems of
unit metric for torque is the Newton meter and Augur
boring machine on the more modest side, might produce a
peak torque of about four hundred newton meters or two
(13:44):
foot pounds of force. I've got a lot more to
say about these tunneling machines, but first let's take a
quick break to thank our sponsor the honors. Rotational force
transfers to the cutting head of this boring machine. These
(14:05):
components make contact with what's called the cutting face of
the dig that's the part of the earth or rock
that the cutting head is actually making contact with. The
cutting head is the surface that goes against the rocks, boulders,
and sand. So this cutting surface can have numerous tools
on it, including cutting disks which are used mostly to
(14:26):
break up rocks and boulders, scrapers and other projections meant
to remove material to excavate it, to break it up,
excavate it and move it back into the back part
of this tunneling machine. They also typically have gaps in
the face of the cutting head that allows this spoil
(14:47):
to pass through the cutting head and move back through
the chain. Uh the spoil is able to come through
that way, it encounters the auger blade that acts like
a conveyor screw, and the auger blade will pull the
spoil or muck away from the cutting surface. Now, not
all cutting tools are suitable for all types of ground. Some,
(15:10):
like the cutting disks, like I said, are really good
for breaking up larger rocks and boulders into smaller pieces.
But if you're encountering a lot of mud or water
in this tunneling job, a different selection might be needed
in order to dig the tunnel and to convey the
material to the conveyor screw and maintain the cutting faces stability.
Wet ground presents challenges in that regard. I'll talk more
(15:32):
about that in a bit. So the cutting tools tend
to be made from really really hard materials because you
want them to last a good long while, preferably for
the length of the tunneling job. So you might use
something like tungsten carbide, and it's also sometimes just called
carbide for short. And this is a pretty cool material.
(15:53):
So tungsten is more than twice as dense as steel.
The process for making tungsten carbide involves lots of steps,
but essentially you're taking ore that contains tungsten, so something
like wolf from right. Uh. So you take wolf from
right and you crush it. You maybe you treat it
with some chemicals, You heat it up, and you end
(16:15):
up with something like tungsten oxide. Then you treat it
in a carbonizing process, such as heating it to more
than twelve degrees celsius. This removes the oxygen from that
mixture and it binds carbon to the tungsten. Then you
sort out the grains of tungsten carbide into piles based
on grain size. You typically would use something like a
(16:37):
sieve to do this. So you pass through sieves and
you get the finest grains out, and then you go
with progressively larger sieves to get the other grains. You
mix that with some other materials, including cobalt. Cobalt connect
as a binding agent. You press the mixture into a
mold high temperature mold for the whatever tool you're building.
(17:00):
Then you put it into what was called a centering furnace,
which is hot enough to melt the cobalt, which then
binds everything together kind of like the force. Then you
remove the tungsten carbide you and uh then hone it
down to its final size and its final shape. And
I've skipped a lot of details here. Anyone who has
worked with tungsten carbide, who's made the stuff knows that.
(17:21):
But this is a very high level kind of look
at the process. And in the end, what you have
is a tool much stronger than steel that can stand
up to a lot of wear and tear, which is
perfect for cutting into stuff like stone and breaking up rocks.
So the business end of the boring machine is the
cutting head, and that's typically protected by some shielding that
that sort of cylinder that's from the point of the
(17:44):
cutting face and extends back quite a bit. And then
sometimes you might use a length of pipe right behind that,
especially if you're using cutting these utility size holes, then
you would have metal pipe that would be connected to
the cutting head and surrounding the auger blade. On the
(18:07):
really big machines, it's typically part of the boring machine itself.
You don't just have a cutting head that's extending from
a pipe. It's all part of the same machine. This
big shield that will extend back several feet. The shielding
keeps the area near the face stable and it makes
direct contact with the earth that you're cutting through, So
(18:30):
it's it's sort of the tip of the tunneling machine.
So the cutting surface of the toweling machine presses against
the cutting face and turns it up to start digging horizontally.
The pressure is generated by these in the small ones
by the boring machine. It has those tracks I talked
about that's laid down in the pit and it starts
(18:50):
to roll forward, and the rolling forward is what puts
the forward thrust against the the cutting head which makes
contact with the the earth it starts to cut through
and tunnel in. This is a very slow process. It
is not happen quickly at all. So when I say
roll forward, I really just mean putting forward pressure, forward
(19:11):
thrust on that cutting head. Uh. The process itself takes
quite a long time, and the auger is typically wheeled
and has some sort of bracing technology to hold it
into place so that it doesn't just push itself backward
while it's trying to cut through this tunnel. Between the
(19:31):
auger boring machine and the tunneler that you've you're using,
you would lay down this metal pipe that contains the
auger blade and it would attach to either end right,
So one end of the auger blade attaches to the
cutting head, the other end of the auger blade attaches
to the auger boring machine. And then the auger boring
(19:52):
machine starts to turn, the auger blade turning, the cutting
head starts to tunnel into the earth. But obviously this
only allows you to tunnel so far right. Eventually you're
going to push the auger boring machine up against the
point where the tunnel opens up. So what happens then?
How do you go any further? If you're digging a
(20:14):
short tunnel, obviously it's not a problem. But if it's
a long tunnel, what do you do? Well, what you
would do is you would stop the auger boring machine.
You would you would stop your tunneling process. This is
the cutting phase. You'd stop the cutting phase, and you
would detach the auger boring machine from the blade and
the pipe that it was pushing into the tunnel. You
(20:36):
would pull the auger boring machine back to its starting position.
You would then lower into the digging pit a new
length of pipe inside, which is another length of auger blade,
and then you would connect the two lengths of auger
blade together the one that's already in the tunnel and
the new length of auger blade that you've just lowered
(20:58):
into the pit. You would connect the other side to
the auger boring machine, and now you've essentially doubled the
length of your auger blade and you can start up again.
A full dig job might require you do this several times,
and essentially you would keep doing it until the dig
job was done. Uh, if the dig job was super long,
(21:18):
this is problematic because eventually you're going to get to
a length where the auger boring machine is not going
to be able to generate the torque necessary to turn
that long of a blade and the cutting head. But
generally speaking, that's how it works. You just keep on
lowering extensions into the pit, connecting it to the part
that's already been pushed into the tunnel, and start up again.
(21:39):
It's actually kind of neat. There are a lot of
videos on YouTube that show this process. I watched tons
of them because it was I don't know, I was
turned into like a little kid again watching construction videos. Now,
for the larger boring machines, the really big ones that
are digging tunnels for like, you know, cars, or trains
or whatever. There's a really cool method for building out
(22:01):
a tunnel. These machines are way too big to draw
thrust or rotational power from an auger boring machine. You
would not have just a truly enormous auger boring machine
outside in a deep pit. So instead they have all
the mechanical elements incorporated into this enormous tunneler, and there's
so many moving parts that it's hard to keep track
(22:22):
of them all. They have their own rotational motor to
generate that incredible torque needed to turn the cutting heads that,
like I said, can be meters in diameter. Bertha was
seventeen nearly seventeen and a half meters in diameter. You
need a really powerful motor to be able to turn
that with the force necessary for it to start cutting
(22:44):
through the earth. Behind the cutting head, typically you have
a chamber. There are a couple of different major types
of tunneling machines, so these chambers can serve slightly different purposes,
And I guess I should go ahead and break them
down because it all has to do with the type
of material your dig through. If it's pretty much solid
rock you're digging through, you could use what's called an
(23:05):
open tunnel boring machine. These do not have the protective
shielding cylinder that extends back from the cutting head. They're
just open because they're cutting through essentially stone, and they
the rest of the machine is just straight behind it,
unprotected for the most part, and the machine would use
(23:26):
hydraulic grippers to brace against the walls of the tunnel
it was building and to provide the forward thrust needed
for it to make contact with the cutting face to
keep on cutting crews behind it would add support systems
to the tunnel like rock bolts and wire mesh, and
that would help support the tunnel as it was being dug.
(23:48):
But otherwise you don't have to have any additional stuff.
You know, you you have like a conveyor to move
the spoil away from the cutting head and down the tunnel,
but otherwise eyes you don't need all the other bits
and pieces. For soft ground, however, you might need something
like an earth pressure balance machine. These machines have a
(24:08):
shield to keep the tunnel supported around the end of
the boring machine. So this is that cylinder I was
talking about that extends back from the cutting head. They
hold up the tunnel from uh that that's made immediately
behind the cutting head, otherwise it would just collapse in
on itself. Behind the cutting head, there's a chamber and
(24:30):
that's where the muck or spoil comes into the tunneler.
There's a screw conveyor that then can take that stuff
out of this chamber, and the screw conveyor can turn
at different speeds, and the reason why you would want
to alter the speed of the conveyor is to control
the amount of pressure inside that chamber. The pressure can
(24:54):
help keep the cutting face stable. So if you need
more pressure to keep the cutting face stable, maybe there's
water that would otherwise come into the system, then the
screw conveyor can slow down. It can remove material more
slowly from the chamber, and it creates more pressure so
that the tunnel doesn't just flood and collapse in on itself.
(25:18):
If less pressure is needed, the screw conveyor can speed
up and remove more material from the chamber and that
decreases the pressure behind the cutting head. There's another soft
ground tunneling machine type called a slurry shield, which is
for ground that has really high water pressure inside it,
or is made up of very granular particles like sand
or gravel or some types of clay. And with these
(25:40):
boring machines you create a pressurized slurry. You use a
material called bentonite clay and you suspend it in water
and this helps create the hydrostatic pressure needed to keep
the cutting face stable during tunneling, and it also acts
as away to transport muck back away in the cutting head.
(26:01):
In this case, the muck ends up being almost liquid
or gelatinous in nature, so this mixture can be injected
into the cutting face through pressurized nozzles. It's like it's
like you're squirting out this bentnite stuff in front of
the tunneler and this creates a sort of membrane that
protects against the exterior water pressure and it keeps water
(26:22):
from rushing into the tunneling machine. The excavated material and
slurry mixture can be pumped back out of the tunnel.
Instead of using a screw conveyor, you're actually using pipes
and pumps to pump it out the back. Then you
can process it, and some of that material you might
even use in construction, so you might reclaim some of that,
not just dump it as spoil. Now next I'm gonna
(26:45):
explain how these large tunneling machines could keep digging underground
even in soft earth, and how they build the solid
tunnel behind them. But first let's take another quick break
to thank our sponsor. So in these soft earth tunneling machines,
(27:06):
there's an apparatus that is just inside the shielded section
near the cutting head, so it's protected by that cylinder
I was talking about. This device is an erector. It
puts up rings of concrete in segments uh there. The
segments can be several meters in length. That all depends
upon the diameter of the tunnel you're digging. So what
(27:29):
the erector does is there's a conveyor that will pull
prefabricated segments of concrete rings to the erector. The erector
comes down, picks up each segment and then places them
as part of the tunnel wall. So it does this
piece by piece, and it ends with a wedge shape
(27:50):
piece called the keystone. The segments of concrete ring essentially
snapped together. They use things like dowels and holes to
snap together, and they also are bolted together. And the
concrete ring acts as a tunnel interior. And it's also
while the tunneling machine uses to push off of to
use as thrust when tunneling. So the small borders I
(28:13):
talked about earlier do this in too processes two stages really,
so do the large ones. So first, let's say that
you've been tunneling for a while, right, You've set up
several meters of tunnel, so the process has been going
on for a few days. Hydraulic arms on the tunneling
(28:33):
machine press against the edge, the outer edge of the ring,
the one that's furthest inside the tunnel. So it's as
far as you've gone, and in constructing this tunnel, this
is still under the protective shielding of that cylinder I
was talking about. So you have these hydraulic arms that
are pressing on that outer edge. Those hydraulic arms exert
(28:57):
pressure and create force to put the cutting head against
the cutting face. So they as they extend, they're at
their creating that forward thrust for the cutting head, so
it's actually pushing the cutting head against the earth. Now,
this tends to go really really slowly, and once all
those hydraulic arms have extended all the way, they can't
(29:19):
go any further. That means you're not going to get
any more forward thrust, the tunneling phase ends and the
erector moves into place, and now we move into the
second phase, the building phase. So for each segment of ring,
the respective hydraulic arms that are pushing against that outer
edge will withdraw, and that gives the erector the enough
(29:42):
room to snap the next ring section into place. Once
it has done that, the hydraulic arms can extend again
and brace against this new section of ring. And once
you've completed a whole ring segment, you've extended the tunnel
by one more ring. Now each ring might be you know,
(30:02):
a meter or so in with so you've just extended it.
Then the next tunneling phase can begin. All the hydraulic
arms are now closer in their one ring segment further contracted,
so they can start extending again and they can create
thrust again. And so you do this in this sort
of seesaw approach. You tunnel, you stop, you build, the
(30:25):
building creates the space you need in order to create
the thrust, and you tunnel again. It's actually pretty interesting,
and there's a lot of videos that show this. I
know it's kind of hard to envision from audio, but
I highly recommend if you want to check this out,
you can look for tunneling machine videos to see the
process I'm talking about. So what happens though if you
(30:46):
need to turn as you're tunneling, Because what I've been
describing works really well if you're going in a straight line.
But if you're in one of these big machines and
you need to make that tunnel curve a bit, well,
for those sections, you might use ring segments that are conical,
which means that by changing the direction of this cone
(31:08):
shape you can create a curve. And plus you have
these hydraulic arms behind the cutting head that can exert
different levels of thrust and turn the direction of the
cut just slightly so like the left side is pushing
out a little further than the right side. That starts
to create the curve that you need in order to
(31:30):
meet whatever the shape of the tunnel needs to be.
Over time, this creates these really long curves. Now, these
machines do not go very fast. The cutting head might
only turn two or three times per minute, and according
to the Boring Company, your average snail is a speed
demon compared to a tunnel boring machine can move fourteen
(31:53):
times faster than a tunneling machine as it travels a
straight line, and tunneling also is really expensive and again
according to the boring Company, a mile of tunnel could
cost up to one billion dollars depending upon the project.
These are really big obstacles that stand in the way
of building out tunnel systems to allow for underground travel
(32:15):
in some of the busiest cities in the world. So
the boring Company hopes to bring both the time it
takes to complete a project down and the cost down.
To increase speed, the Boring Company is increasing the cutting
speed of the cutting head, so they're increasing the number
of rotations it does per minute. This also requires building
(32:35):
out other systems like cooling systems to help keep the
bearings and other components at the right nominal operating temperatures.
The company is also developing machines that will not have
to alternate between digging and the building phases, so that
they can just keep cutting continuously. They don't have to
cut stop, build a segment of ring, cut stop, build
(32:58):
a segment of ring. The company also proposes using the
excavated earth when possible, to make bricks, which might then
be used to line the tunnel itself, which would cut
down the need for making concrete, and that's environmentally a
good thing because concrete production causes a lot of pollution.
Nearly five percent of the world's greenhouse gas emissions comes
(33:19):
from concrete production. In early November two eighteen, Elon Musk
tweeted out a video of the Hawthorne Test tunnel. That's
a route that leads from SpaceX Is parking lot and
moves under street near Los Angeles for about two miles.
And the tunnel is supposed to open on December tenth,
(33:40):
two eighteen, and they're supposed to be a big opening
celebration event that day and on the following day, the
boring company will offer free rides to the public in
the tunnel, which sounds pretty exciting. Meanwhile, these sorts of
tunneling machines are being used all over the world to
dig out subway systems. The tunnel Bertha Ug in Seattle
(34:01):
is a replacement for the Alaskan Way Viaduct that's an
elevated highway in Seattle, so instead of building up, they're
building down. The project was originally supposed to take two
and a half years to complete. Instead it took nearly
four years due to various setbacks, one of which happened
early early on in the progress project when um they
(34:21):
encountered a steel rod that was underground. And UM they've
also had a few attempts by various Washington politicians to
kill the whole project. They were saying that it was
um an embarrassment, it was a waste. But it kept
on going and it did complete. The tunneling process ended
in April. The tunnel as of the recording of this
(34:44):
podcast isn't open yet. It's not scheduled for use until
February twenty nineteen. But once Bertha finished the digging process,
it broke through into what was called a disassembly pit,
where it was well, just a bold Bertha would not
be used to dig any more tunnels. Instead, anything that
could be melted down and recycled was and everything else
(35:07):
was kind of, you know, thrown away. The massive machine
was cut up into twenty ton pieces, but since the
machine weighed seven thousand two tons, that took a long time.
Since tunneling ended, engineers have been building a double deck
highway inside the tunnel that Bertha dug. And that's all
(35:28):
I have to say about these tunneling machines. They are
really interesting. Uh. The more I looked into them, the
more I was fascinated by how enormous the big ones
are and the fact that it's a machine that also
is like a construction site all by itself is pretty phenomenal.
And just seeing how simple things like the Archimedes screw
(35:49):
could be incorporated into these machines to move massive amounts
of earth. It also speaks to the ingenuity of the
ancient designers like Archimedes who came up with these ideas
that we're still finding uses for today, These these simple
machines that are still the best way to do certain things.
I think it's pretty interesting and I really look forward
(36:09):
to finding out how Elon Musk's boring company is able
to advance the technology. And maybe pretty soon we'll have
underground tunnels in all major cities that make getting around
much much easier. I would look forward to that too.
If you guys have any suggestions for future topics I
should cover in tech Stuff, why not visit our website.
(36:31):
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(36:54):
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(37:14):
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(37:37):
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