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