Speaker 1: Welcome to Brainstuff, a production of iHeartRadio. Hey brain Stuff
Speaker 1: Lauren Vogebon Here. With winter coming on fast here in
Speaker 1: the Northern Hemisphere, I've been thinking about travel, but not
Speaker 1: travel through the cold, wet weather. What if we could
Speaker 1: reach a beautiful destination via underwater tunnel. Unfortunately, contrary to
Speaker 1: what supervillains and Moleman would have you believe, it takes
Speaker 1: more than some giant machine to build an underwater tunnel.
Speaker 1: Even so, for most of human history we've been pretty
Speaker 1: tunnel savvy. Humans have tunneled since the first cave dwellers
Speaker 1: decided to excavate a spare bedroom, and the essentials of
Speaker 1: dig support and advance were well refined by the time
Speaker 1: the ancient Greeks used tunnels to irrigate and drain their farmland.
Speaker 1: Even underwater tunneling is old. Sometime around twenty one seventy BCE,
Speaker 1: the Babylonia built one of the first known examples by
Speaker 1: diverting the Euphrates River. The bricklined and arch supported tunnel
Speaker 1: measured twelve feet high by fifteen feet wide that's four
Speaker 1: by five meters, and provided passage for pedestrians and chariots
Speaker 1: alike between the royal palace and a temple some three
Speaker 1: thousand feet or nine hundred meters away. For centuries, tunnels
Speaker 1: were employed mainly by miners and medieval sappers, who dug
Speaker 1: under castle walls to collapse them, hence the term undermine.
Speaker 1: But the advent of canal transport and later railroads gave
Speaker 1: workers something new to sink their shovels into. The eighteenth
Speaker 1: thirty twentieth centuries saw a succession of ever more challenging
Speaker 1: tunnel projects, made possible by vast improvements in surveying and
Speaker 1: ventilation techniques. Even so, a danger and expense delayed attempts
Speaker 1: at underwater tunneling until the mid eighteen hundreds, which raises
Speaker 1: the question if underwater tunneling risks in your own grave,
Speaker 1: literally and financially, why bother. Many city planners agree turning
Speaker 1: to tunnels only when congested bridges reach choking capacity. But
Speaker 1: bridges are problematic too. They interfere with shipping traffic, take
Speaker 1: up valuable riverfront property, and block scenic views. From a
Speaker 1: defense standpoint, bridges make easy airstrike targets and can constitute
Speaker 1: hazards if they collapse. Tunnels conversely, withstand tides currents and
Speaker 1: storms better than bridges, can reach longer distances and have
Speaker 1: virtually unlimited weight carrying capacity. In addition, a tunnel's per
Speaker 1: length cost drops as it gets longer, whereas for bridges
Speaker 1: the opposite is true, and while tunnels require a larger
Speaker 1: initial investment, bridges make up the difference in maintenance costs.
Speaker 1: But let's not get tunnel vision. Tunneling faces particular security
Speaker 1: vulnerabilities and safety issues of fires and accidents post die
Speaker 1: threats in tunnels, which is why rail tunnels include crossover
Speaker 1: passages where trains can switch tracks, along with service tunnels
Speaker 1: that can serve as emergencies scape routes. Yet today underwater
Speaker 1: tunnels are so commonplace that we rarely think of them
Speaker 1: as the modern wonders that they are. Take the Seikan
Speaker 1: Tunnel in Japan, a connecting the islands of Honshu and Hokkaido,
Speaker 1: which holds the record for the longest and deepest underwater
Speaker 1: rail tunnel at thirty three and a half miles that's
Speaker 1: fifty four kilometers, reaching a depth of seven hundred and
Speaker 1: ninety feet or two hundred and forty meters. Japan began
Speaker 1: planning it in the nineteen fifties after a typhoon caused
Speaker 1: a deadly disaster in the strait between the islands. It
Speaker 1: took thirty years to complete, and pumps keep it clear
Speaker 1: of water at the rate of twenty tons per minute.
Speaker 1: As impressive as the Seikon Tunnel is, only about fourteen
Speaker 1: of its miles or twenty three of its kilometers run underwater,
Speaker 1: meaning that the Channel Tip or chunnel that connects the
Speaker 1: United Kingdom in France beats it. There. The channel only
Speaker 1: goes a third is deep, but its underwater portion runs
Speaker 1: for twenty four miles or about thirty eight and a
Speaker 1: half kilometers. It was finished in nineteen ninety four, but okay,
Speaker 1: the Sekan and Channel tunnels respectively blasted and bored their
Speaker 1: passages through solid rock. The longest and deepest immersion tunnel
Speaker 1: is the Marmarai, which connects the Asian and European halves
Speaker 1: of Istanbul Turkey across the floor of the Bosporus Sea.
Speaker 1: It employs pre assembled sections connected by thick, flexible rubber
Speaker 1: reinforced steel plates to better contend with regional seismic activity,
Speaker 1: and stretches a total of eight miles or thirteen kilometers,
Speaker 1: but let's back up a bit and get into some
Speaker 1: technical but important definitions. A tunnel is technically a passage
Speaker 1: dug entirely underground, and many of the subterranean tubes that
Speaker 1: we consider tunnels, like subway and sewage and water lines,
Speaker 1: are technically conduits because to build them we temporarily remove
Speaker 1: ground material, place the line, then cover it back up,
Speaker 1: which is generally much cheaper and easier, especially if you're
Speaker 1: dealing with loose dirt and shallow projects. But to tunnel
Speaker 1: in the earth under a body of water, the classic
Speaker 1: approach is to use a tunneling shield. Shields let you
Speaker 1: dig a long tunnel through soft earth without its bleeding
Speaker 1: edge collapsing. Here's how it works, okay, Imagine you take
Speaker 1: a coffee can and take off the lid, then sharpen
Speaker 1: the edge around the bottom and punch a few holes
Speaker 1: in the bottom. If you took that tin by the
Speaker 1: open end and pushed the bottom into soft earth, some
Speaker 1: dirt would squeeze up through the holes. You could remove
Speaker 1: the dirt and then push the can in further. On
Speaker 1: the scale of a real shield. Several humans as sometimes
Speaker 1: nicknamed muckers or sandhogs, would stand inside compartments within the
Speaker 1: can and remove the clayer sand. Hydraulic jacks would gradually
Speaker 1: move the shield forward while crews behind it installed metal
Speaker 1: supporting rings, then lined them with concrete or masonry. In
Speaker 1: order to hold back water seepage from the tunnel walls.
Speaker 1: The front of the tunnel or shield is sometimes pressurized
Speaker 1: with compressed air. Workers who can only withstand short periods
Speaker 1: in such conditions must pass through one or more air
Speaker 1: locks and take precautions against pressure related sickness. Shields are
Speaker 1: still used in tunnel construction, especially when installing utility conduits
Speaker 1: or larger water or sewage pipes. Although labor intensive, they
Speaker 1: cost only a fraction as much as their mammoth cousins.
Speaker 1: The tunnel boring machines afar from dull. A tunnel boring
Speaker 1: machine is a multi story tall engine of destruction capable
Speaker 1: of chewing through solid rock at its front spins its
Speaker 1: cutting head, which is a giant wheel that has bristles
Speaker 1: of rock breaking discs, and incorporates a system of scoops
Speaker 1: to lift the pummeled rock and drop it onto an
Speaker 1: outbound conveyor belt. Behind the cutting head swings an erector,
Speaker 1: which is a rotating assembly that builds the tunnel lining
Speaker 1: in the machine's wave. In some large projects, like the Channel,
Speaker 1: a separate tunnel boring machines begin on opposite ends and
Speaker 1: drill toward a central point, using sophisticated surveying methods to
Speaker 1: keep them on course. Drilling through solid rock creates largely
Speaker 1: self supporting tunnels, and these machines drive forward quickly and relentlessly.
Speaker 1: Some Channel machines could bore two hundred and fifty feet
Speaker 1: a day, that's seventy six meters. On the downside, they
Speaker 1: break often and deal poorly with rock that's worn, sheared,
Speaker 1: or highly jointed, so they sometimes move much slower. Luckily,
Speaker 1: tunnel boring machines and shields aren't the only games in town.
Speaker 1: Enter these sunken two tube or immersed tube tunnel. These
Speaker 1: entirely evade the problem of trying to dig through soft
Speaker 1: earth or solid rock while preventing a whole ocean from
Speaker 1: pouring into your tunnel by constructing the tunnel separately then
Speaker 1: installing it under water. Immersion tunnels are assembled on site
Speaker 1: from prefab pieces, each the size of a football field.
Speaker 1: American engineer W. J. Wilgis pioneered the technique when he
Speaker 1: built the Detroit River Railroad tunnel connecting Detroit, Michigan, and Windsor, Ontario,
Speaker 1: in nineteen ten, and they've been the go to technique
Speaker 1: for vehicle tunnels ever since. To make each segment, workers
Speaker 1: assemble some thirty thousand tons of stealing concrete enough for
Speaker 1: a ten story apartment building in a massive mold, then
Speaker 1: allow the concrete to cure for nearly a month. The
Speaker 1: molds contain the tunnel's floor, walls, and ceiling and are
Speaker 1: initially capped at the ends to keep them water tight
Speaker 1: as they're transported out to sea. Immersion pontoons, which are
Speaker 1: large ships resembling a cross between a gantry crane and
Speaker 1: a pondtoon boat, do the hauling. Once they're over the
Speaker 1: pre dug sea trench. Each tunnel section is weighted to
Speaker 1: allow it to sink. A crane slowly lowers the section
Speaker 1: into position while divers guide it precisely to its GPS coordinates.
Speaker 1: Each new section is connected to its predecessor with a
Speaker 1: massive flexible joint that can establish a seal on the
Speaker 1: outside of the two tubes. Crews then pump out the
Speaker 1: water between the two bulkhead seals on the inside of
Speaker 1: the seal, and then can remove the bulkheads, at which
Speaker 1: point you're ready to sink a new piece and connect
Speaker 1: it the same way. Once the tunnel is built and
Speaker 1: reinforced from the inside, it might be buried under backfill
Speaker 1: or otherwise covered. Immersed tube construction can delve deeper than
Speaker 1: other approaches. Because the technique doesn't require compressed air to
Speaker 1: hold water at bay, A cruise can for work longer
Speaker 1: in them and under more tolerable conditions. Moreover, sections of
Speaker 1: an immersed tunnel can take any form, unlike a board tunnel,
Speaker 1: which follows the shape of its shield or boring machine. However,
Speaker 1: immersed tunnels do require additional tunneling methods to prepare the
Speaker 1: bed and bore out their land based entrances and exits.
Speaker 1: Researchers are working on developing submerged but floating tunnels that
Speaker 1: would circumvent the need to bore at all. In underwater tunneling,
Speaker 1: as in life, it takes all kinds. Today's episode is
Speaker 1: based on the article how do you build an underwater tunnel?
Speaker 1: On how stuffworks dot com, written by Nicholas Gerbis. Brain
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