December 6, 2024 • 11 mins
It's relatively common for cars and trains to pass through underwater tunnels, but these structures are marvels of modern engineering. Learn how they're blasted, bored, and built from prefab pieces in today's episode of BrainStuff, based on this article: https://science.howstuffworks.com/engineering/structural/build-underwater-tunnel.htm
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Episode Transcript
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Speaker 1 (00:01):
Welcome to Brainstuff, a production of iHeartRadio. Hey brain Stuff
Lauren Vogebon Here. With winter coming on fast here in
the Northern Hemisphere, I've been thinking about travel, but not
travel through the cold, wet weather. What if we could
reach a beautiful destination via underwater tunnel. Unfortunately, contrary to
(00:26):
what supervillains and Moleman would have you believe, it takes
more than some giant machine to build an underwater tunnel.
Even so, for most of human history we've been pretty
tunnel savvy. Humans have tunneled since the first cave dwellers
decided to excavate a spare bedroom, and the essentials of
dig support and advance were well refined by the time
(00:48):
the ancient Greeks used tunnels to irrigate and drain their farmland.
Even underwater tunneling is old. Sometime around twenty one seventy BCE,
the Babylonia built one of the first known examples by
diverting the Euphrates River. The bricklined and arch supported tunnel
measured twelve feet high by fifteen feet wide that's four
(01:10):
by five meters, and provided passage for pedestrians and chariots
alike between the royal palace and a temple some three
thousand feet or nine hundred meters away. For centuries, tunnels
were employed mainly by miners and medieval sappers, who dug
under castle walls to collapse them, hence the term undermine.
(01:30):
But the advent of canal transport and later railroads gave
workers something new to sink their shovels into. The eighteenth
thirty twentieth centuries saw a succession of ever more challenging
tunnel projects, made possible by vast improvements in surveying and
ventilation techniques. Even so, a danger and expense delayed attempts
(01:51):
at underwater tunneling until the mid eighteen hundreds, which raises
the question if underwater tunneling risks in your own grave,
literally and financially, why bother. Many city planners agree turning
to tunnels only when congested bridges reach choking capacity. But
bridges are problematic too. They interfere with shipping traffic, take
(02:15):
up valuable riverfront property, and block scenic views. From a
defense standpoint, bridges make easy airstrike targets and can constitute
hazards if they collapse. Tunnels conversely, withstand tides currents and
storms better than bridges, can reach longer distances and have
virtually unlimited weight carrying capacity. In addition, a tunnel's per
(02:37):
length cost drops as it gets longer, whereas for bridges
the opposite is true, and while tunnels require a larger
initial investment, bridges make up the difference in maintenance costs.
But let's not get tunnel vision. Tunneling faces particular security
vulnerabilities and safety issues of fires and accidents post die
(03:00):
threats in tunnels, which is why rail tunnels include crossover
passages where trains can switch tracks, along with service tunnels
that can serve as emergencies scape routes. Yet today underwater
tunnels are so commonplace that we rarely think of them
as the modern wonders that they are. Take the Seikan
Tunnel in Japan, a connecting the islands of Honshu and Hokkaido,
(03:22):
which holds the record for the longest and deepest underwater
rail tunnel at thirty three and a half miles that's
fifty four kilometers, reaching a depth of seven hundred and
ninety feet or two hundred and forty meters. Japan began
planning it in the nineteen fifties after a typhoon caused
a deadly disaster in the strait between the islands. It
(03:43):
took thirty years to complete, and pumps keep it clear
of water at the rate of twenty tons per minute.
As impressive as the Seikon Tunnel is, only about fourteen
of its miles or twenty three of its kilometers run underwater,
meaning that the Channel Tip or chunnel that connects the
United Kingdom in France beats it. There. The channel only
(04:05):
goes a third is deep, but its underwater portion runs
for twenty four miles or about thirty eight and a
half kilometers. It was finished in nineteen ninety four, but okay,
the Sekan and Channel tunnels respectively blasted and bored their
passages through solid rock. The longest and deepest immersion tunnel
is the Marmarai, which connects the Asian and European halves
(04:27):
of Istanbul Turkey across the floor of the Bosporus Sea.
It employs pre assembled sections connected by thick, flexible rubber
reinforced steel plates to better contend with regional seismic activity,
and stretches a total of eight miles or thirteen kilometers,
but let's back up a bit and get into some
(04:48):
technical but important definitions. A tunnel is technically a passage
dug entirely underground, and many of the subterranean tubes that
we consider tunnels, like subway and sewage and water lines,
are technically conduits because to build them we temporarily remove
ground material, place the line, then cover it back up,
(05:09):
which is generally much cheaper and easier, especially if you're
dealing with loose dirt and shallow projects. But to tunnel
in the earth under a body of water, the classic
approach is to use a tunneling shield. Shields let you
dig a long tunnel through soft earth without its bleeding
edge collapsing. Here's how it works, okay, Imagine you take
(05:32):
a coffee can and take off the lid, then sharpen
the edge around the bottom and punch a few holes
in the bottom. If you took that tin by the
open end and pushed the bottom into soft earth, some
dirt would squeeze up through the holes. You could remove
the dirt and then push the can in further. On
the scale of a real shield. Several humans as sometimes
(05:55):
nicknamed muckers or sandhogs, would stand inside compartments within the
can and remove the clayer sand. Hydraulic jacks would gradually
move the shield forward while crews behind it installed metal
supporting rings, then lined them with concrete or masonry. In
order to hold back water seepage from the tunnel walls.
The front of the tunnel or shield is sometimes pressurized
(06:18):
with compressed air. Workers who can only withstand short periods
in such conditions must pass through one or more air
locks and take precautions against pressure related sickness. Shields are
still used in tunnel construction, especially when installing utility conduits
or larger water or sewage pipes. Although labor intensive, they
(06:40):
cost only a fraction as much as their mammoth cousins.
The tunnel boring machines afar from dull. A tunnel boring
machine is a multi story tall engine of destruction capable
of chewing through solid rock at its front spins its
cutting head, which is a giant wheel that has bristles
of rock breaking discs, and incorporates a system of scoops
(07:02):
to lift the pummeled rock and drop it onto an
outbound conveyor belt. Behind the cutting head swings an erector,
which is a rotating assembly that builds the tunnel lining
in the machine's wave. In some large projects, like the Channel,
a separate tunnel boring machines begin on opposite ends and
drill toward a central point, using sophisticated surveying methods to
(07:25):
keep them on course. Drilling through solid rock creates largely
self supporting tunnels, and these machines drive forward quickly and relentlessly.
Some Channel machines could bore two hundred and fifty feet
a day, that's seventy six meters. On the downside, they
break often and deal poorly with rock that's worn, sheared,
(07:48):
or highly jointed, so they sometimes move much slower. Luckily,
tunnel boring machines and shields aren't the only games in town.
Enter these sunken two tube or immersed tube tunnel. These
entirely evade the problem of trying to dig through soft
earth or solid rock while preventing a whole ocean from
(08:09):
pouring into your tunnel by constructing the tunnel separately then
installing it under water. Immersion tunnels are assembled on site
from prefab pieces, each the size of a football field.
American engineer W. J. Wilgis pioneered the technique when he
built the Detroit River Railroad tunnel connecting Detroit, Michigan, and Windsor, Ontario,
(08:31):
in nineteen ten, and they've been the go to technique
for vehicle tunnels ever since. To make each segment, workers
assemble some thirty thousand tons of stealing concrete enough for
a ten story apartment building in a massive mold, then
allow the concrete to cure for nearly a month. The
molds contain the tunnel's floor, walls, and ceiling and are
(08:54):
initially capped at the ends to keep them water tight
as they're transported out to sea. Immersion pontoons, which are
large ships resembling a cross between a gantry crane and
a pondtoon boat, do the hauling. Once they're over the
pre dug sea trench. Each tunnel section is weighted to
allow it to sink. A crane slowly lowers the section
(09:16):
into position while divers guide it precisely to its GPS coordinates.
Each new section is connected to its predecessor with a
massive flexible joint that can establish a seal on the
outside of the two tubes. Crews then pump out the
water between the two bulkhead seals on the inside of
the seal, and then can remove the bulkheads, at which
(09:37):
point you're ready to sink a new piece and connect
it the same way. Once the tunnel is built and
reinforced from the inside, it might be buried under backfill
or otherwise covered. Immersed tube construction can delve deeper than
other approaches. Because the technique doesn't require compressed air to
hold water at bay, A cruise can for work longer
(10:01):
in them and under more tolerable conditions. Moreover, sections of
an immersed tunnel can take any form, unlike a board tunnel,
which follows the shape of its shield or boring machine. However,
immersed tunnels do require additional tunneling methods to prepare the
bed and bore out their land based entrances and exits.
(10:22):
Researchers are working on developing submerged but floating tunnels that
would circumvent the need to bore at all. In underwater tunneling,
as in life, it takes all kinds. Today's episode is
based on the article how do you build an underwater tunnel?
On how stuffworks dot com, written by Nicholas Gerbis. Brain
(10:44):
Stuff is production by Heart Radio in partnership with HowStuffWorks
dot Com and is produced by Tyler Klang. For more
podcasts my Heart Radio, visit the iHeartRadio app, Apple Podcasts,
or wherever you listen to your favorite shows.
Welcome to Brainstuff, a production of iHeartRadio. Hey brain Stuff
Lauren Vogebon Here. With winter coming on fast here in
the Northern Hemisphere, I've been thinking about travel, but not
travel through the cold, wet weather. What if we could
reach a beautiful destination via underwater tunnel. Unfortunately, contrary to
(00:26):
what supervillains and Moleman would have you believe, it takes
more than some giant machine to build an underwater tunnel.
Even so, for most of human history we've been pretty
tunnel savvy. Humans have tunneled since the first cave dwellers
decided to excavate a spare bedroom, and the essentials of
dig support and advance were well refined by the time
(00:48):
the ancient Greeks used tunnels to irrigate and drain their farmland.
Even underwater tunneling is old. Sometime around twenty one seventy BCE,
the Babylonia built one of the first known examples by
diverting the Euphrates River. The bricklined and arch supported tunnel
measured twelve feet high by fifteen feet wide that's four
(01:10):
by five meters, and provided passage for pedestrians and chariots
alike between the royal palace and a temple some three
thousand feet or nine hundred meters away. For centuries, tunnels
were employed mainly by miners and medieval sappers, who dug
under castle walls to collapse them, hence the term undermine.
(01:30):
But the advent of canal transport and later railroads gave
workers something new to sink their shovels into. The eighteenth
thirty twentieth centuries saw a succession of ever more challenging
tunnel projects, made possible by vast improvements in surveying and
ventilation techniques. Even so, a danger and expense delayed attempts
(01:51):
at underwater tunneling until the mid eighteen hundreds, which raises
the question if underwater tunneling risks in your own grave,
literally and financially, why bother. Many city planners agree turning
to tunnels only when congested bridges reach choking capacity. But
bridges are problematic too. They interfere with shipping traffic, take
(02:15):
up valuable riverfront property, and block scenic views. From a
defense standpoint, bridges make easy airstrike targets and can constitute
hazards if they collapse. Tunnels conversely, withstand tides currents and
storms better than bridges, can reach longer distances and have
virtually unlimited weight carrying capacity. In addition, a tunnel's per
(02:37):
length cost drops as it gets longer, whereas for bridges
the opposite is true, and while tunnels require a larger
initial investment, bridges make up the difference in maintenance costs.
But let's not get tunnel vision. Tunneling faces particular security
vulnerabilities and safety issues of fires and accidents post die
(03:00):
threats in tunnels, which is why rail tunnels include crossover
passages where trains can switch tracks, along with service tunnels
that can serve as emergencies scape routes. Yet today underwater
tunnels are so commonplace that we rarely think of them
as the modern wonders that they are. Take the Seikan
Tunnel in Japan, a connecting the islands of Honshu and Hokkaido,
(03:22):
which holds the record for the longest and deepest underwater
rail tunnel at thirty three and a half miles that's
fifty four kilometers, reaching a depth of seven hundred and
ninety feet or two hundred and forty meters. Japan began
planning it in the nineteen fifties after a typhoon caused
a deadly disaster in the strait between the islands. It
(03:43):
took thirty years to complete, and pumps keep it clear
of water at the rate of twenty tons per minute.
As impressive as the Seikon Tunnel is, only about fourteen
of its miles or twenty three of its kilometers run underwater,
meaning that the Channel Tip or chunnel that connects the
United Kingdom in France beats it. There. The channel only
(04:05):
goes a third is deep, but its underwater portion runs
for twenty four miles or about thirty eight and a
half kilometers. It was finished in nineteen ninety four, but okay,
the Sekan and Channel tunnels respectively blasted and bored their
passages through solid rock. The longest and deepest immersion tunnel
is the Marmarai, which connects the Asian and European halves
(04:27):
of Istanbul Turkey across the floor of the Bosporus Sea.
It employs pre assembled sections connected by thick, flexible rubber
reinforced steel plates to better contend with regional seismic activity,
and stretches a total of eight miles or thirteen kilometers,
but let's back up a bit and get into some
(04:48):
technical but important definitions. A tunnel is technically a passage
dug entirely underground, and many of the subterranean tubes that
we consider tunnels, like subway and sewage and water lines,
are technically conduits because to build them we temporarily remove
ground material, place the line, then cover it back up,
(05:09):
which is generally much cheaper and easier, especially if you're
dealing with loose dirt and shallow projects. But to tunnel
in the earth under a body of water, the classic
approach is to use a tunneling shield. Shields let you
dig a long tunnel through soft earth without its bleeding
edge collapsing. Here's how it works, okay, Imagine you take
(05:32):
a coffee can and take off the lid, then sharpen
the edge around the bottom and punch a few holes
in the bottom. If you took that tin by the
open end and pushed the bottom into soft earth, some
dirt would squeeze up through the holes. You could remove
the dirt and then push the can in further. On
the scale of a real shield. Several humans as sometimes
(05:55):
nicknamed muckers or sandhogs, would stand inside compartments within the
can and remove the clayer sand. Hydraulic jacks would gradually
move the shield forward while crews behind it installed metal
supporting rings, then lined them with concrete or masonry. In
order to hold back water seepage from the tunnel walls.
The front of the tunnel or shield is sometimes pressurized
(06:18):
with compressed air. Workers who can only withstand short periods
in such conditions must pass through one or more air
locks and take precautions against pressure related sickness. Shields are
still used in tunnel construction, especially when installing utility conduits
or larger water or sewage pipes. Although labor intensive, they
(06:40):
cost only a fraction as much as their mammoth cousins.
The tunnel boring machines afar from dull. A tunnel boring
machine is a multi story tall engine of destruction capable
of chewing through solid rock at its front spins its
cutting head, which is a giant wheel that has bristles
of rock breaking discs, and incorporates a system of scoops
(07:02):
to lift the pummeled rock and drop it onto an
outbound conveyor belt. Behind the cutting head swings an erector,
which is a rotating assembly that builds the tunnel lining
in the machine's wave. In some large projects, like the Channel,
a separate tunnel boring machines begin on opposite ends and
drill toward a central point, using sophisticated surveying methods to
(07:25):
keep them on course. Drilling through solid rock creates largely
self supporting tunnels, and these machines drive forward quickly and relentlessly.
Some Channel machines could bore two hundred and fifty feet
a day, that's seventy six meters. On the downside, they
break often and deal poorly with rock that's worn, sheared,
(07:48):
or highly jointed, so they sometimes move much slower. Luckily,
tunnel boring machines and shields aren't the only games in town.
Enter these sunken two tube or immersed tube tunnel. These
entirely evade the problem of trying to dig through soft
earth or solid rock while preventing a whole ocean from
(08:09):
pouring into your tunnel by constructing the tunnel separately then
installing it under water. Immersion tunnels are assembled on site
from prefab pieces, each the size of a football field.
American engineer W. J. Wilgis pioneered the technique when he
built the Detroit River Railroad tunnel connecting Detroit, Michigan, and Windsor, Ontario,
(08:31):
in nineteen ten, and they've been the go to technique
for vehicle tunnels ever since. To make each segment, workers
assemble some thirty thousand tons of stealing concrete enough for
a ten story apartment building in a massive mold, then
allow the concrete to cure for nearly a month. The
molds contain the tunnel's floor, walls, and ceiling and are
(08:54):
initially capped at the ends to keep them water tight
as they're transported out to sea. Immersion pontoons, which are
large ships resembling a cross between a gantry crane and
a pondtoon boat, do the hauling. Once they're over the
pre dug sea trench. Each tunnel section is weighted to
allow it to sink. A crane slowly lowers the section
(09:16):
into position while divers guide it precisely to its GPS coordinates.
Each new section is connected to its predecessor with a
massive flexible joint that can establish a seal on the
outside of the two tubes. Crews then pump out the
water between the two bulkhead seals on the inside of
the seal, and then can remove the bulkheads, at which
(09:37):
point you're ready to sink a new piece and connect
it the same way. Once the tunnel is built and
reinforced from the inside, it might be buried under backfill
or otherwise covered. Immersed tube construction can delve deeper than
other approaches. Because the technique doesn't require compressed air to
hold water at bay, A cruise can for work longer
(10:01):
in them and under more tolerable conditions. Moreover, sections of
an immersed tunnel can take any form, unlike a board tunnel,
which follows the shape of its shield or boring machine. However,
immersed tunnels do require additional tunneling methods to prepare the
bed and bore out their land based entrances and exits.
(10:22):
Researchers are working on developing submerged but floating tunnels that
would circumvent the need to bore at all. In underwater tunneling,
as in life, it takes all kinds. Today's episode is
based on the article how do you build an underwater tunnel?
On how stuffworks dot com, written by Nicholas Gerbis. Brain
(10:44):
Stuff is production by Heart Radio in partnership with HowStuffWorks
dot Com and is produced by Tyler Klang. For more
podcasts my Heart Radio, visit the iHeartRadio app, Apple Podcasts,
or wherever you listen to your favorite shows.
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