Stuff You Should Know - How Underwater Tunnels Work

Episode Date: December 12, 2013

It's a pretty amazing feat to dig a tunnel beneath a body of water that's big enough (and safe enough) to drive a train through. While humans have been digging underwater tunnels for thousands of years, it wasn't until the late 19th century that it became viable on a large scale. In this episode, Chuck and Josh explore the ins and outs of the engineering triumph that is digging below water. Learn more about your ad-choices at https://www.iheartpodcastnetwork.comSee omnystudio.com/listener for privacy information.

I'm Munga Shatikler and it turns out astrology is way more widespread than any of us want to believe. You can find it in Major League Baseball, International Banks, K-Pop groups, even the White House. But just when I thought I had a handle on this subject, something completely unbelievable happened to me and my whole view on astrology changed. Whether you're a skeptic or a believer, give me a few minutes because I think your ideas are about to change too.

Just a Skyline drive on the iHeart Radio app, Apple Podcast, or wherever you get your podcasts. On the podcast, HeyDude the 90s called, David Lacher and Christine Taylor, stars of the cult classic show HeyDude, bring you back to the days of slip dresses and choker necklaces. We're going to use HeyDude as our jumping off point, but we are going to unpack and dive back into the decade of the 90s. We lived it and now we're calling on all of our friends to come back and relive it. Listen to HeyDude the 90s called on the iHeart Radio app, Apple Podcasts, or wherever you get your podcasts.

Brought to you by the all new 2014 Toyota Corolla. Welcome to Stuff You Should Know from HowStuffWorks.com. Hey and welcome to the podcast, I'm Josh Clark, there's Charles W. Chuck Bryant, Noel is with us again. That's right. Actually it's just been a very short period of time since he was last with us. Well who knows, we might release these weeks apart. Just to throw people.

You know? It's possible. How you doing? Fine. How are you? I'm good man. I'm great. I'm ready to tunnel through the show and get all on up out of here.

That's pretty lame. It was okay. It worked though because what we're talking about has to do with tunnels. Yes. I don't know if you caught that. Yeah we covered a little bit of this in the Subways podcast. Yeah, cut and cover. Cut and cover, but this goes deep under cut and cover.

You gotta stop this. I know. Yeah, we're talking about underwater tunnels specifically. That's right. Which by the way we should probably say for those of you who are into semantics, the word tunnel is applied only to something that is bored entirely underground. Yes. If you say like we talked about with cut and cover in Subways, if you dig out a trench,

put in your tunnel and then backfill over your tunnel, what you've created is a conduit. And if you correct people when they talk about this kind of thing, that means you're so obnoxious. Or you're an engineer of some sort. Yeah, but engineers don't even do that because they so want to be liked. You know, they don't want to be that guy. Yeah, so we're talking about how and I think a lot of people wonder how did you manage to get a tunnel under the water? We're going to tell you.

It's really not that hard. And there's a few ways. Yeah. I don't know if saying it's not that hard is correct. Well not that complicated in an engineering sense. No, I think none of these like I was like, what, right? They bore a tunnel under a river. Right.

But just the this is the overview. I mean, you can read this article and build an underwater railway tunnel. Is that what you thought I was saying? No, no, I'm just saying like there's so much more to like just the details. Yeah. I mean, but you weren't saying that there's particle physics and there's digging a big hole under a river, you know what I'm saying? And we're going to hear from some angry civil engineer.

No, I think it's great. I think it's modern modern marvel is what it is. It is. Yeah. So Chuck. Yes. It's not necessarily modern. Yeah, that's true.

You know, people have been digging under rivers since the Babylonians. Yeah. I was quite surprised by this. They managed to build a 3000 foot brick lined art supported tunnel 12 by 15 feet under while they diverted the Euphrates River. And it was a pedestrian passageway. That's crazy. Right.

This is 2180 BCE. Right. I think they diverted it temporarily. Well, yeah, sure. But even still, it's still a tunnel and they still did this several thousand years ago. And they diverted a river, which is impressive in its own. I'm impressed with them. I'm glad to hear you are too.

Over the years, people kind of, I imagine, built and failed spectacularly in trying to build underwater. It wasn't until the 19th century that people really kind of started to advance by leaps and bounds over, say, the Babylonian methods to come up with some techniques that are still in use today. Yeah. As far as underwater goes, I mean, they were tunneling all during the 18th and 19th centuries. And in fact, the word under mine, I thought was fairly interesting.

It came from the fact that there were miners who dug under castle walls to collapse them. That's a pretty good idea. Yeah. It's a very good idea. And I don't think we covered that in our castle podcast either. No. I wish we had. Yeah.

That would have been complete. Now I know that that episode is incomplete. But like you said, it was the 1800s when we finally said, hey, let's try this underwater thing again because we think we can do it now. Yeah. And they kind of had it licked and again, like I said, some of the techniques that they came up with at this time are still in use today. Yeah.

I got a question for you though. Okay. If it's dangerous and it's pricey, why do you tunnel at all? Why not just build bridges? That is a fantastic question. And I happen to have some answers. Okay. All right.

So think about this. You build a bridge. It makes sense. Yeah. It's beautiful. Bridge works. We know how to build bridges. We've been doing it forever.

A heavily trafficked shipping lane with ships that are taller than your bridge. You can build a drawbridge, but it's going to be up and down, up and down, up and down all day. Yeah. And don't fool yourself. A drawbridge is pretty expensive too. Sure. That's one.

All right. If you are an enemy of the United States, your bridge could be a target from airstrikes. Yeah. That's a problem for you. If you, I mean, if you want to build it again afterward, it could be struck down again and then again. Sure. You want your bridges to remain intact.

Yes. I'm going to argue for tunnels here though, my friend, and say that they withstand tides very well in currents and storms. It's not out in the open like a bridge is. You can go greater distances with a tunnel and you can carry like almost virtually unlimited amounts of weight. So score one for tunnel and chuck. Yeah, because with the bridge, you have to worry about it collapsing.

With the tunnel, it's like, no, you're probably pretty firm against some sort of bedrock or seabed or something like that. You can put as many trucks as you want on it. It's not going to break. Yeah. I guess we'd call seismic activity a draw. Have you ever seen that? It's probably not good for either one.

You have the bridges? Yeah. Yeah. That is nuts. Was that in Seattle or Washington? I don't know, man, but you look at that and think, how does that move like that without just completely breaking apart? It does.

Pretty scary. So we're going to call that a draw, though, because earthquakes are not good for either. Well, at cost, you said that bridges are costly. Well, bridges get costlier the bigger they are, whereas tunnels get cheaper the bigger they are. Yeah. The length with the tunnel, the cost starts to drop as it gets longer and longer. Not so with the bridge.

So why then would city planners still use tunneling as a last sort of a last resort? I guess because they like bridges more. Okay. All right. So that was and scene. We were play acting. It's not very well, either. No, I thought it was pretty good.

Oh, you did? Yeah. I thought it was okay. So let's talk about some of the tunnels they've got going on these days that are pretty remarkable. There's one that actually connects two islands in Japan. It's called the, well, you're the resident Japanese expert. How do you pronounce that? The Saikon Tunnel.

The Saikon Tunnel? Saikon. And that is the one of those two holds the record for the longest and deepest underwater rail tunnel. And they did that in the 1950s after a typhoon sank some ferry boats and the Sugaru Strait and killed like over 1400 people. They said, you know what, maybe we should go underwater with this operation. Yeah.

And they did so. And it connects Honshu and Hokkaido. And Hokkaido is known for its sub factories. I knew you would have a tidbit for me. The Simpsons tidbit. Oh, was that from the Mr. Sparkle episode? Oh man, one of the best ever. So in 1988, they completed the Saikon, Saikon Tunnel.

Yeah. I'm going to go with Saikon. And it stretches 33 and a half miles. Yeah. The whole tunnel does. Yeah. That's impressive. It is.

But then only 14 and a half miles of it, only 14 and a half miles of it, are underwater tunnel. Yeah. But it goes close to 800 feet deep, which is, that's sort of the remarkable part. That's a long way down. Yeah. You have to pop your ears when you're on that train. Oh, I'm sure.

The tunnel, which we were laughing about before we hit record. That's the name. I know. And we should say it's called the Tunnel because it's actually the Channel Tunnel. It goes under the English Channel to connect the UK and France. Yes. And that was finished in the mid-90s. And 24 of its 31 miles are underwater, but it only goes about 246 feet down.

Yes. Still impressive. Only. Yeah. It's so funny to use words like only with stuff like this or just. Yeah. And then the newest member to the underwater tunnel family is the Marmaray Tunnel in Istanbul that connects the Asian portion of Istanbul and the European portion of Istanbul, which

means it's the only underwater tunnel or the first to connect two continents. That's right. And the name comes from the sea of Marmara and the word Rey, which is Turkish for rail, because it is another rail tunnel. Yeah. And it's pretty cool when they started digging it. This thing, this project went slow as molasses, not just because of construction, but because they came upon the port of Theodosius, theodosius, I think.

Is that right? Sounds good to me. So it was a port in Istanbul. Back then it was Constantinople. That was the busiest port in the world for about a thousand years. And it was lost. Yeah. And they came upon it while digging this tunnel and the archaeologists were like, okay, stop,

stop, stop. You got a turn. Yeah. They found 40,000 artifacts from this. No, they didn't turn. They went through it. Yeah. But they documented everything and grabbed it for the museums.

Well, if it hadn't been for the tunnel, maybe they would have never found that stuff, you know. No, really? So that was an immersion tunnel and it was the longest and deepest immersion tunnel ever built. Immersion tunnels are my favorite. Yeah. That's the one that I didn't think was super complicated.

I saw a couple of videos and I'm telling you, there's a lot to it. Just the pontoons alone are... Yeah, but it's like the kind of thing you can replicate in your bathtub. Right. That's what I mean by complicated. I see what you mean. Okay. Okay.

In the 1990s called David Lasher and Christine Taylor, stars of the cult classic show, Hey Dude, bring you back to the days of slip dresses and choker necklaces. We're going to use Hey Dude as our jumping off point, but we are going to unpack and dive back into the decade of the 90s. We lived it and now we're calling on all of our friends to come back and relive it. It's a podcast packed with interviews, co-stars, friends, and non-stop references to the best decade ever. Do you remember going to Blockbuster?

Do you remember Nintendo 64? Do you remember getting frosted tips? Was that a cereal? No, it was hair. Do you remember AOL Instant Messenger and the dial-up sound like poltergeist? So leave a code on your best friend's beeper because you'll want to be there when the nostalgia starts flowing. Each episode will rival the feeling of taking out the cartridge from your Game Boy, blowing

on it and popping it back in as we take you back to the 90s. Listen to Hey Dude, the 90s called on the iHeart radio app, Apple Podcasts, or wherever you get your podcasts. I'm Mangesh Atikulur and to be honest, I don't believe in astrology, but from the moment I was born, it's been a part of my life. In India, it's like smoking. You might not smoke, but you're going to get secondhand astrology. And lately, I've been wondering if the universe has been trying to tell me to stop running

and pay attention because maybe there is magic in the stars if you're willing to look for it. We rounded up some friends and we dove in and let me tell you, it got weird fast. Tantric curses, Major League Baseball teams, cancelled marriages, K-pop. But just when I thought I had a handle on this sweet and curious show about astrology, my whole world came crashing down. Situation doesn't look good. There is risk to father.

And my whole view on astrology? It changed. Whether you're a skeptic or a believer, I think your ideas are going to change too. Listen to Skyline Drive and the I Heart Radio app, Apple Podcast, or wherever you get your podcasts. So we're going to get into what that all means because there are quite a few ways to build tunnels and three, yeah, and there are three in use. I bet there's other dudes out there trying to figure new stuff out.

But one of the oldest that is still in use, it's called a tunneling shield, thanks to a remarkable, remarkable dude, a Frenchman named Marc Isambard Brunel, who was eventually knighted for his work as inventing the tunnel shield. Understandably so. Yeah. It was a big invention. Pretty amazing. He got the idea from watching a shipworm, there's like a naked clam, there's these little

shells on one end. It's basically, yeah, it's like the termite of the sea is what they call it, because this thing bores into docks and boats and basically tunnels into wood and leaves sawdust in his wake. And this guy saw this and he's like, hey, that's a pretty good idea. I think we'll make a tunneling shield. Exactly. Yeah.

So he came up with the Brunel shield, which is actually rectangular, but the best way to think of what a modern tunneling shield looks like, there's a description given in this article that makes sense if you add one extra sentence, you take a coffee can, imagine a coffee can without its lid and the bottom part of the coffee can is pointed somewhat with some holes in it. Yeah. And we dig it into the ground and then turn it on its side to bore horizontally. What you have is something like a tunneling shield.

So at the front end, what part did they miss? They're going straight down and it just completely confused me. The fact that it wasn't going to the side, I couldn't wrap my head around it until I finally was like, oh, I see what they're saying. So that coffee can, imagine it jammed horizontally underground. Let's go in and explore it, right? In the front, there's holes and you have different kind of compartments where people stand. They're called muckers and they dig out the dirt in front of them, right?

Yeah. In Brunel's case, they were cast iron shutters and they would just open these shutters one at a time and just dig a few inches out and back then they used screw jacks, but now they use hydraulics and just inch away, forward little by little. Little by little and then reinforcing them, building the sides as you go. Right. And that coffee can in the meantime is holding that tunnel shape, right? Because it's the exact shape of the tunnel shield.

Yeah. Because in front of digging, the coffee can is giving them all support and then right behind it are masons and steel workers who are reinforcing the tunnel. And then the reinforced finished concrete tunnel provides the stability for those hydraulic jacks that slowly and little by little inch the whole thing forward. Yeah. I mean, it's like every tunnel, although actually the immersion tunnels aren't, but when you're digging a tunnel, it goes back to the Babylonians, you dig, support, advance, dig, support, advance.

Right. Just like Charles Bronson in The Great Escape. Oh yeah. Was that his mantra? No. This was just, I'm going to go tunneling this tunnel and build the frame. You did a good Bronson. Well, it's sort of Bronson, but it's also sort of the guy from the Simpsons who is based

on Bronson. Hank Azaria. Is that who does that? Sure. Okay. Yeah. I don't know that for sure. But is it?

I'm positive. Oh, okay. It's Simpsons reference number two. Oh yeah. Nice. But remember In The Great Escape too, they needed, and of course we'll see this too. It's a very dangerous job and they needed air. So they had the, I think, fire bellows, bellows, something pumping bellows just to pump fresh

air in there. Right. Because when you're 100 feet in a tunnel underground, especially the size of one, The Great Escape, just like big enough for your body. Yeah. You're going to run out of air. Yeah. Well, that's something that they ran into.

We talked about, I don't remember what episode it was, but we were talking about building the Brooklyn Bridge. They had these basically an upright coffee can that they dug the posts out of. Yeah. This is the same. They ran in the same thing when they were building the tunnel underneath the Thames River thanks to Brunel. He'd built it with his son.

Yeah, very short, like 1,200 feet, but it took about eight or nine years. Yeah. There was a shutdown for seven years because it ran out of money, but it was deep enough so that you had to pump compressed air in to keep the water out. Yeah. And since there was compressed air, you had to go through a series of air locks or else you'd get the bent. Sure.

And I don't know if we said this. It seems obvious, but the reason you're doing all this is because digging into soft earth is problematic because your leading edge is going to continually want to collapse on top of you. Unless you have compressed air to keep the water at bay and you have guys digging out through a support structure, e.g. a tunneling shield. Sand hogs. That's method one.

Yes. And it's an old one and it's a good one. It's still in use today. It has to be softer. You can't dig through bedrock because this thing moves through hydraulic jacks and there's guys digging. If you run into some serious rock, the best thing to use is called a tunnel boring machine. Yeah.

If you've ever seen Die Hard 3, you get a good glimpse at these. That was Jeremy Irons. Yeah. It's a pretty good one. In fact, well, actually, yeah, one of only two good ones. Sam Jackson? Yeah. The first one and that one were pretty good.

The second one and I didn't, all the other ones were just terrible. The second one, it wasn't so bad. It was all right. I'd love to see it again. It was at the airport. Yeah. It was okay. I love any kind of airport disaster flick at all.

Oh, yeah, man. I'm crazy for those movies, airport, airport 77, airport 82, whatever. Yeah. Airplane. Love them. What about that bad Tom Hanks movie where he played the foreign guy that lived in the airport? I never saw that.

But did you know? The terminal. Was it in a real guy? Yeah. Yeah. It says so in the movie. I didn't know that. I didn't see the movie.

It wasn't very good. I think the fact that it was kind of lighthearted and warm, that's not what the guy was like. Yeah. Well, Spielberg, plus Tom Hanks doing accents. Man, have you seen him doing Walt Disney? Yeah. I thought that looked okay in the preview. No?

I can't tell. I did. I managed to get through only about 20 minutes of Cloud Atlas the other night. Oh, man. I mean, I just can't see Tom Hanks as like this cockney, rough, roughy, and I mean, I love the guy. He's an amazing actor, but it just didn't work. No.

Why did they do that to him? I don't know. Hodgman's got some good stories about Tom Hanks, by the way. I don't know if you should be telling people that. No. I'm not going to tell the stories. I don't even know if you should say. Okay.

Yes. All right. Man, that was a nice Hanksian sidebar. Yeah. Tunnel boring machines die hard, two, three. Yeah. So these things are like a couple of stories tall. Yeah.

They're amazing. They're tunnel boring machines is the right word for them. They're all inclusive machines. They cut, they support, and they build as they go along. They're magnificent as far as mechanical engineering goes. Yeah. A spinning cutting head needs basically huge, giant steel wheels that twist and turn in different directions.

And then that whole thing turns, and it's just a destructo mobile that goes straight ahead and lifts that, pummels that rock and shoots it out on a conveyor behind it. Yeah. Yeah. Just all in one motion. It's like a five-alve, a shipworm. And this is the part I didn't get, that they're actually building it with an erector as it goes.

Yeah. Man, that's crazy. Yeah. It's all this one big machine that you just basically press start and it goes forward. Yeah. And they actually used tunnel boring machines, a pair of them, for the channel construction. Yeah. One from one side and one from the other side.

And thanks to GPS, good GPS, they were able to keep them on a course for one another. Yeah. The first thing I thought was I would end up like 10 feet above. Oh, man. I wouldn't even end up that close. Yeah. I need to be screwed. You'd have to start all over.

Mine would end up in Scotland. Yeah. Well, that'd be great. Yeah. We'd be like, just tunnel up and get drunk. Yeah. It's where some distilleries. But luckily they had a lot smarter people than us working on the channel.

Right. They drive forward at a rate of about 250 feet per day. That's significant because we're talking like bedrock. Yeah. You know, like if you were able to take away all of the dirt and all of the water on earth, what you would have is rock. That's the mantle. And that's what you're digging through is this rock.

It's made to support the earth. Exactly. Heck, it is the earth. And this is what these machines dig through at a rate of 250 feet a day. That's impressive. Yeah. When they work, apparently they're something this violent is prone to breaking down. So I guess when you have them up and running, that's a good thing.

When they're down, then you're obviously going to be losing time. Did you see how the author of this article put it? I did. I didn't even want to comment. You want to go ahead? Well, he just says that they break down more often than he used Jaguar. I think he probably said Jaguar. Jaguar.

Yeah. I didn't know that or Jaguar, so they famous for not working. Yeah. Oh, yeah. Oh, really? Didn't know that. The older ones are. Well, that's like any old car, right?

I think they and like VW rabbits had like really bad track records. Oh, I remember the rabbit or the Cabriolet. Yeah. Every sorority girl's favorite car. Right. What else? I remember Le Carr. Yeah.

It even said Le Carr on the side. Yeah. It's French for the car. Is it? All right, so did you know, Josh, that they have been banding about the idea of a transit climate tunnel for decades? It's pretty awesome. I don't think it'll ever happen, though.

No, they would be very costly because it would be an immersion tube, but they wouldn't be able to go to the seafloor, obviously, because that's just crazy. It would be tethered, floating essentially at about 150 feet below the water. Right. Dangling from a pontoon on the surface. Yeah. And 54,000 football field size sections. And that's how we're going to get into that in a minute, but that's how they work with

these immersion tunnels. They do it one section at a time. It's just too much money and too much stuff. Well, there's actually an immersion tube tunnel that's proposed in Norway across the Sagna fjord. That sounds much more manageable than the Atlantic Ocean. Really? I mean, just the idea of this pontoon getting pummeled by cyclones and just bad weather

in general. Plus, why do it? Are these people who just want to drive to England from New York? I don't know. I don't know the logic behind any advantage behind something like that. It just seems like it would just, every foot of it is a potential for it to just break and the whole thing's trashed. Yeah.

But the one in Norway, is that an ITT, an immersion tube tunnel? It is dangling from a pontoon above. Oh, OK. That one's dangling. Right. So that technology exists. Well, it's in proposal stage, and the thing I saw was still probably kind of an overview, but they seemed pretty confident about it.

They had like, you know, title charts and all that kind of stuff. But it's only something that's like 20 kilometers or 30 kilometers, something like that. It's not all the way across the Atlantic Ocean. Gotcha. You know. All right. So I guess we should fully explain the ITT then, which is our final way that you can tunnel underground.

And again, my favorite. But before we get to it, let's do a message break. OK. On the podcast, Hey Dude, the 90s called David Lasher and Christine Taylor, stars of the cult classic show, Hey Dude, bring you back to the days of slip dresses and choker necklaces. We're going to use Hey Dude as our jumping off point, but we are going to unpack and dive back into the decade of the 90s. We lived it.

And now we're calling on all of our friends to come back and relive it. It's a podcast packed with interviews, co-stars, friends and non-stop references to the best decade ever. Do you remember going to Blockbuster? Do you remember Nintendo 64? Do you remember getting frosted tips? Was that a cereal? No, it was hair.

Do you remember AOL instant messenger and the dial-up sound like poltergeist? So leave a code on your best friend's beeper because you'll want to be there when the nostalgia starts flowing. Each episode will rival the feeling of taking out the cartridge from your Game Boy, blowing on it and popping it back in as we take you back to the 90s. Listen to Hey Dude, the 90s, called on the iHeart radio app, Apple Podcasts, or wherever you get your podcasts. I'm Mangesh Atikular and to be honest, I don't believe in astrology, but from the moment

I was born, it's been a part of my life. In India, it's like smoking. You might not smoke, but you're going to get secondhand astrology. And lately, I've been wondering if the universe has been trying to tell me to stop running and pay attention. Because maybe there is magic in the stars, if you're willing to look for it. So I rounded up some friends and we dove in and let me tell you, it got weird fast. Tantric curses, Major League Baseball teams, cancelled marriages, K-pop.

But just when I thought I had to handle on this sweet and curious show about astrology, my whole world came crashing down. And it doesn't look good, there is risk to father. And my whole view on astrology, it changed. Whether you're a skeptic or a believer, I think your ideas are going to change too. Listen to Skyline Drive and the iHeart Radio app, Apple Podcasts, or wherever you get your podcasts. And Chuck, now we finally get to talk about my favorite type of tunneling, the Immersion

Tube Tunnel. That's right. So these rubber seals have GINA gaskets, actually is what they're called. And you winch the two together and you pump the water out and these gaskets and seals, the change in water pressure compresses them and creates an airtight seal. But it's underwater. So you would go in, say we want an underground tunnel going from this part of land to that part of land, under here.

So we're just going to go in, we're going to dredge and dig and create a trench where we're going to eventually put the tunnel. But we're going to make the tunnel in individual pieces here on dry land, usually at some sort of shipyard. And they're going to use the equivalent of steel and concrete to make an average size 10 story building. So just tip it on its side and that's what your section looks like. That's one section.

And then once the concrete cures after a month, we'll take it out to sea in a pontoon crane, which is exactly what it sounds like, but they're gigantic. We seal it up first so that it floats. Sure. Can't have it sinking yet. Right. And then once we do get it over the site roughly where we want it, we will kind of start to sink it a little bit.

Or I've also seen they'll weight it down and then they'll sink the thing. And eventually they'll link it up to another segment. So they use winches to pull one segment to another. And then these rubber gaskets hold the seal. And in this bulkheads, these temporary bulkheads that are keeping the two segments separate, inside the tunnel you couldn't go through them yet. You pump the water out, that changes air pressure, compresses the rubber gaskets forming a water tight seal.

Then you remove the steel bulkheads. Bam, there's two connected segments of the tunnel, and you just keep adding and adding and adding and adding until you've created your prefab underwater tunnel. It's beautiful. Then you cover that up, backfill it or something with rock. And we have a guy named W.J. Wilgus to thank for this, because he invented it way back in the early 1900s. Yeah, that is an early 1900s name.

Oh yeah. W.J. Wilgus. The Merced Tube Tunnel, where the world's fast. And everyone said this is a pretty good idea. Yeah. And he pioneered the technique when he built the Detroit River Railroad Tunnel connecting Michigan to Canada.

So technically, the first Merced Tube Tunnel is a sewer line in Boston in 1894. And when he built that railway line, that was like, okay, this thing works. Because we've been shuttling poop in Boston. Exactly. Like now we can do it with trains, and you are now the man of the hour, W.J. Because what is a train except a lot of poop, you know? There is a similarity in principle. But that has been the go-to since then, and there's been more than 100 of these built

in the 20th century alone, and that didn't even count the 21st century. No. So I don't even know what's been going on the past 13 years. I saw like an engineering thing that referred to them as rare, but I don't have the impression that they're rare at all. They're not rare. They're kind of like the go-to technique for any, well, as many as possible. Yeah.

Well, the one advantage is that you can make them any shape. It's not like when you have a tunnel boring machine, it's going to have the shape of the tunnel bore. Or same with the tunnel shield as well. Yeah, I guess so. It's the size of the giant coffee can. But you can make a tunnel in the shape of a diamond if you wanted to. Right.

Well, maybe not diamond. Well, you could. It'd be kind of crazy. It'd be a big waste of money. But yeah, you can take any shape. And you will also have to use some of those other methods eventually, because this is just for the what's along the bottom, to get down to that section and then out the entrances and exits.

You're going to have to use some other methods. Right. You might have to tunnel through some sort of rock or whatever. But yeah, when you put these tunnel segments in and you pump the water out of the chamber that connects the two, you take the bulkheads off, like there's your finished tunnel right there. I mean, you've got the floors, the walls, the ceiling, the roadway. You go in and put the wiring in and the lighting and all that stuff afterward.

But your tunnel's set. Yeah. I just think it's neat. I think it's very neat. What else you got? I got nothing else. There's one proposed right now that will be the longest immersed tube tunnel in the world when it's finished in 2016.

There's a 50 kilometer bridge that connects or will connect Hong Kong to Macau. And part of it is a 6.7 kilometer long immersed tube tunnel, which will probably be real nice. Awesome. Yeah. I guess that's it. All right. Go forth and build tunnels. Go forth and build underwater tunnels.

That's right. Let's see. If you want to learn more about underwater tunnels, you can type that word in the search bar at HowStuffWorks.com. And since I said search bar, that means it's time for listener mail. All right. I'm going to call this another chess email. And this is going to be it on the chess emails.

But thank you to everyone who wrote in about your chess strategies and stuff. It's pretty great. Hey, guys. Thanks for doing the podcast on chess. It's a great game. Here are a few things that you sort of missed. Jumping, Josh implied, or maybe even outright said that a knight only appears to jump over other pieces, but really just goes around them.

Knights actually can jump over other pieces. For example, if you were so inclined on your very first move, you could jump your knight over your pawns and place it in front of the rest of your pieces. There aren't any empty spaces to take your knight around your islands in the stream. So that's jumping, baby. A little more on castling, a couple of things. As you said, you cannot castle if either piece involved has moved during the game. You also can't do it if the king is in check or has to move through check to castle.

So the opposition queen is attacking a square that the king has to go through to castle it. It cannot be done. Yeah. Yeah. You got that? Yeah. You should probably all go back, rewind that and listen to it again.

That's right. And that's from Matt in Pittsburgh. I'm sorry, in LA via Pittsburgh. But I did want to point out someone else in another correction. And I think we got the pawn promotion right, like if you make, get your pawn all the way to the other end of the table. But I don't think we pointed out that you can only promote it to a piece that you've already lost.

No, we definitely did not. In other words, you can't have two queens. Okay. But if you lost your queen. I specifically said you'd have two queens. Oh, you did? Yeah. Okay.

I genuinely didn't know that. I thought that. I didn't catch that. I knew that, but I didn't catch it. So that was from someone else. Yeah. In LA via Pittsburgh. Yeah.

Thanks. And he was the other person. Yeah. He also described on Passant, but I think we've already taken that up in another listener mail. Yeah. Thanks for all the corrections on Chester. Yeah, everybody.

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