WEBVTT - How Do We Build Tunnels Underwater?

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<v Speaker 1>Welcome to Brainstuff, a production of iHeartRadio. Hey brain Stuff

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<v Speaker 1>Lauren Vogebon Here. With winter coming on fast here in

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<v Speaker 1>the Northern Hemisphere, I've been thinking about travel, but not

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<v Speaker 1>travel through the cold, wet weather. What if we could

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<v Speaker 1>reach a beautiful destination via underwater tunnel. Unfortunately, contrary to

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<v Speaker 1>what supervillains and Moleman would have you believe, it takes

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<v Speaker 1>more than some giant machine to build an underwater tunnel.

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<v Speaker 1>Even so, for most of human history we've been pretty

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<v Speaker 1>tunnel savvy. Humans have tunneled since the first cave dwellers

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<v Speaker 1>decided to excavate a spare bedroom, and the essentials of

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<v Speaker 1>dig support and advance were well refined by the time

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<v Speaker 1>the ancient Greeks used tunnels to irrigate and drain their farmland.

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<v Speaker 1>Even underwater tunneling is old. Sometime around twenty one seventy BCE,

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<v Speaker 1>the Babylonia built one of the first known examples by

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<v Speaker 1>diverting the Euphrates River. The bricklined and arch supported tunnel

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<v Speaker 1>measured twelve feet high by fifteen feet wide that's four

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<v Speaker 1>by five meters, and provided passage for pedestrians and chariots

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<v Speaker 1>alike between the royal palace and a temple some three

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<v Speaker 1>thousand feet or nine hundred meters away. For centuries, tunnels

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<v Speaker 1>were employed mainly by miners and medieval sappers, who dug

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<v Speaker 1>under castle walls to collapse them, hence the term undermine.

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<v Speaker 1>But the advent of canal transport and later railroads gave

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<v Speaker 1>workers something new to sink their shovels into. The eighteenth

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<v Speaker 1>thirty twentieth centuries saw a succession of ever more challenging

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<v Speaker 1>tunnel projects, made possible by vast improvements in surveying and

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<v Speaker 1>ventilation techniques. Even so, a danger and expense delayed attempts

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<v Speaker 1>at underwater tunneling until the mid eighteen hundreds, which raises

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<v Speaker 1>the question if underwater tunneling risks in your own grave,

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<v Speaker 1>literally and financially, why bother. Many city planners agree turning

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<v Speaker 1>to tunnels only when congested bridges reach choking capacity. But

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<v Speaker 1>bridges are problematic too. They interfere with shipping traffic, take

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<v Speaker 1>up valuable riverfront property, and block scenic views. From a

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<v Speaker 1>defense standpoint, bridges make easy airstrike targets and can constitute

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<v Speaker 1>hazards if they collapse. Tunnels conversely, withstand tides currents and

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<v Speaker 1>storms better than bridges, can reach longer distances and have

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<v Speaker 1>virtually unlimited weight carrying capacity. In addition, a tunnel's per

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<v Speaker 1>length cost drops as it gets longer, whereas for bridges

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<v Speaker 1>the opposite is true, and while tunnels require a larger

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<v Speaker 1>initial investment, bridges make up the difference in maintenance costs.

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<v Speaker 1>But let's not get tunnel vision. Tunneling faces particular security

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<v Speaker 1>vulnerabilities and safety issues of fires and accidents post die

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<v Speaker 1>threats in tunnels, which is why rail tunnels include crossover

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<v Speaker 1>passages where trains can switch tracks, along with service tunnels

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<v Speaker 1>that can serve as emergencies scape routes. Yet today underwater

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<v Speaker 1>tunnels are so commonplace that we rarely think of them

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<v Speaker 1>as the modern wonders that they are. Take the Seikan

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<v Speaker 1>Tunnel in Japan, a connecting the islands of Honshu and Hokkaido,

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<v Speaker 1>which holds the record for the longest and deepest underwater

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<v Speaker 1>rail tunnel at thirty three and a half miles that's

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<v Speaker 1>fifty four kilometers, reaching a depth of seven hundred and

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<v Speaker 1>ninety feet or two hundred and forty meters. Japan began

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<v Speaker 1>planning it in the nineteen fifties after a typhoon caused

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<v Speaker 1>a deadly disaster in the strait between the islands. It

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<v Speaker 1>took thirty years to complete, and pumps keep it clear

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<v Speaker 1>of water at the rate of twenty tons per minute.

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<v Speaker 1>As impressive as the Seikon Tunnel is, only about fourteen

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<v Speaker 1>of its miles or twenty three of its kilometers run underwater,

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<v Speaker 1>meaning that the Channel Tip or chunnel that connects the

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<v Speaker 1>United Kingdom in France beats it. There. The channel only

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<v Speaker 1>goes a third is deep, but its underwater portion runs

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<v Speaker 1>for twenty four miles or about thirty eight and a

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<v Speaker 1>half kilometers. It was finished in nineteen ninety four, but okay,

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<v Speaker 1>the Sekan and Channel tunnels respectively blasted and bored their

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<v Speaker 1>passages through solid rock. The longest and deepest immersion tunnel

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<v Speaker 1>is the Marmarai, which connects the Asian and European halves

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<v Speaker 1>of Istanbul Turkey across the floor of the Bosporus Sea.

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<v Speaker 1>It employs pre assembled sections connected by thick, flexible rubber

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<v Speaker 1>reinforced steel plates to better contend with regional seismic activity,

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<v Speaker 1>and stretches a total of eight miles or thirteen kilometers,

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<v Speaker 1>but let's back up a bit and get into some

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<v Speaker 1>technical but important definitions. A tunnel is technically a passage

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<v Speaker 1>dug entirely underground, and many of the subterranean tubes that

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<v Speaker 1>we consider tunnels, like subway and sewage and water lines,

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<v Speaker 1>are technically conduits because to build them we temporarily remove

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<v Speaker 1>ground material, place the line, then cover it back up,

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<v Speaker 1>which is generally much cheaper and easier, especially if you're

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<v Speaker 1>dealing with loose dirt and shallow projects. But to tunnel

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<v Speaker 1>in the earth under a body of water, the classic

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<v Speaker 1>approach is to use a tunneling shield. Shields let you

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<v Speaker 1>dig a long tunnel through soft earth without its bleeding

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<v Speaker 1>edge collapsing. Here's how it works, okay, Imagine you take

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<v Speaker 1>a coffee can and take off the lid, then sharpen

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<v Speaker 1>the edge around the bottom and punch a few holes

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<v Speaker 1>in the bottom. If you took that tin by the

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<v Speaker 1>open end and pushed the bottom into soft earth, some

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<v Speaker 1>dirt would squeeze up through the holes. You could remove

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<v Speaker 1>the dirt and then push the can in further. On

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<v Speaker 1>the scale of a real shield. Several humans as sometimes

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<v Speaker 1>nicknamed muckers or sandhogs, would stand inside compartments within the

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<v Speaker 1>can and remove the clayer sand. Hydraulic jacks would gradually

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<v Speaker 1>move the shield forward while crews behind it installed metal

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<v Speaker 1>supporting rings, then lined them with concrete or masonry. In

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<v Speaker 1>order to hold back water seepage from the tunnel walls.

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<v Speaker 1>The front of the tunnel or shield is sometimes pressurized

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<v Speaker 1>with compressed air. Workers who can only withstand short periods

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<v Speaker 1>in such conditions must pass through one or more air

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<v Speaker 1>locks and take precautions against pressure related sickness. Shields are

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<v Speaker 1>still used in tunnel construction, especially when installing utility conduits

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<v Speaker 1>or larger water or sewage pipes. Although labor intensive, they

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<v Speaker 1>cost only a fraction as much as their mammoth cousins.

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<v Speaker 1>The tunnel boring machines afar from dull. A tunnel boring

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<v Speaker 1>machine is a multi story tall engine of destruction capable

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<v Speaker 1>of chewing through solid rock at its front spins its

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<v Speaker 1>cutting head, which is a giant wheel that has bristles

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<v Speaker 1>of rock breaking discs, and incorporates a system of scoops

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<v Speaker 1>to lift the pummeled rock and drop it onto an

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<v Speaker 1>outbound conveyor belt. Behind the cutting head swings an erector,

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<v Speaker 1>which is a rotating assembly that builds the tunnel lining

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<v Speaker 1>in the machine's wave. In some large projects, like the Channel,

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<v Speaker 1>a separate tunnel boring machines begin on opposite ends and

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<v Speaker 1>drill toward a central point, using sophisticated surveying methods to

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<v Speaker 1>keep them on course. Drilling through solid rock creates largely

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<v Speaker 1>self supporting tunnels, and these machines drive forward quickly and relentlessly.

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<v Speaker 1>Some Channel machines could bore two hundred and fifty feet

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<v Speaker 1>a day, that's seventy six meters. On the downside, they

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<v Speaker 1>break often and deal poorly with rock that's worn, sheared,

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<v Speaker 1>or highly jointed, so they sometimes move much slower. Luckily,

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<v Speaker 1>tunnel boring machines and shields aren't the only games in town.

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<v Speaker 1>Enter these sunken two tube or immersed tube tunnel. These

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<v Speaker 1>entirely evade the problem of trying to dig through soft

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<v Speaker 1>earth or solid rock while preventing a whole ocean from

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<v Speaker 1>pouring into your tunnel by constructing the tunnel separately then

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<v Speaker 1>installing it under water. Immersion tunnels are assembled on site

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<v Speaker 1>from prefab pieces, each the size of a football field.

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<v Speaker 1>American engineer W. J. Wilgis pioneered the technique when he

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<v Speaker 1>built the Detroit River Railroad tunnel connecting Detroit, Michigan, and Windsor, Ontario,

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<v Speaker 1>in nineteen ten, and they've been the go to technique

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<v Speaker 1>for vehicle tunnels ever since. To make each segment, workers

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<v Speaker 1>assemble some thirty thousand tons of stealing concrete enough for

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<v Speaker 1>a ten story apartment building in a massive mold, then

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<v Speaker 1>allow the concrete to cure for nearly a month. The

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<v Speaker 1>molds contain the tunnel's floor, walls, and ceiling and are

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<v Speaker 1>initially capped at the ends to keep them water tight

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<v Speaker 1>as they're transported out to sea. Immersion pontoons, which are

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<v Speaker 1>large ships resembling a cross between a gantry crane and

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<v Speaker 1>a pondtoon boat, do the hauling. Once they're over the

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<v Speaker 1>pre dug sea trench. Each tunnel section is weighted to

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<v Speaker 1>allow it to sink. A crane slowly lowers the section

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<v Speaker 1>into position while divers guide it precisely to its GPS coordinates.

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<v Speaker 1>Each new section is connected to its predecessor with a

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<v Speaker 1>massive flexible joint that can establish a seal on the

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<v Speaker 1>outside of the two tubes. Crews then pump out the

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<v Speaker 1>water between the two bulkhead seals on the inside of

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<v Speaker 1>the seal, and then can remove the bulkheads, at which

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<v Speaker 1>point you're ready to sink a new piece and connect

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<v Speaker 1>it the same way. Once the tunnel is built and

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<v Speaker 1>reinforced from the inside, it might be buried under backfill

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<v Speaker 1>or otherwise covered. Immersed tube construction can delve deeper than

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<v Speaker 1>other approaches. Because the technique doesn't require compressed air to

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<v Speaker 1>hold water at bay, A cruise can for work longer

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<v Speaker 1>in them and under more tolerable conditions. Moreover, sections of

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<v Speaker 1>an immersed tunnel can take any form, unlike a board tunnel,

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<v Speaker 1>which follows the shape of its shield or boring machine. However,

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<v Speaker 1>immersed tunnels do require additional tunneling methods to prepare the

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<v Speaker 1>bed and bore out their land based entrances and exits.

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<v Speaker 1>Researchers are working on developing submerged but floating tunnels that

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<v Speaker 1>would circumvent the need to bore at all. In underwater tunneling,

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<v Speaker 1>as in life, it takes all kinds. Today's episode is

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<v Speaker 1>based on the article how do you build an underwater tunnel?

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<v Speaker 1>On how stuffworks dot com, written by Nicholas Gerbis. Brain

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<v Speaker 1>Stuff is production by Heart Radio in partnership with HowStuffWorks

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<v Speaker 1>dot Com and is produced by Tyler Klang. For more

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<v Speaker 1>podcasts my Heart Radio, visit the iHeartRadio app, Apple Podcasts,

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<v Speaker 1>or wherever you listen to your favorite shows.