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Some proposed underwater tunnel connections are unfeasable
because there's a deep sea trench in the way. On land we
would simply build a viaduct over a canyon, so why not do the
same when building a tunnel?
I would propose a tunnel running under the sea floor up to the
trench's vertical ridge,
where it will emerge from the sea floor
and become a covered viaduct or above-ground tunnel (or
maybe I should call it a vunnel?).
Also. for places where building any kind of conventional
tunnel would be hard, but where a building bridge would also
be cnstrained by shipping or wind, a full underwater viaduct
can be the best solution.
The underwater viaduct thus has the potential to allow for
widespread usage.
Bering Strait Bridge
[pocmloc, Sep 22 2014]
I did the math for buoyancy
https://app.box.com...yopwwxb64csy603btck
thanks all. porpoise, maybe the current effect can be reduced by using a more hydrodynamic shape than just a round tube, for example a double teardrop cross section. Another potential burden is the effect of buoyancy. If you have a 10m inner diameter tunnel, and a one meter thick reinforced concrete shell, then you still have to somehow compensate for 29 metric tons of buoyancy per meter. But this can also be an advantage, since holding it in place with cables to prevent it from floating might be cheaper than building heavy concrete pillars every 10 meters. [sdk16420, Sep 23 2014]
Beaufort's Dyke
http://en.wikipedia...i/Beaufort%27s_Dyke
Projects for a tunnel or Irish Sea fixed link ... have been suggested .... The Dyke has always been an important problem for such proposals [8th of 7, Sep 23 2014]
Force of sea currents
https://app.box.com...it66hike9o6y9t54hzg
Here's the updated pdf with calculation for the force exerted by the sea current added. I get 11 kN of horizontal force per meter of tunnel length. [sdk16420, Sep 25 2014]
Norway plans to build on
http://inhabitat.co...er-traffic-tunnels/
Hah! [sdk16420, Jul 25 2016]
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Annotation:
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If an ocean current is 10 times slower than wind (100 fold less energy), it's still 1000 times more dense. From an energy perspective, this means an underwater viaduct would have to be 10 times stronger than a land-based one. That neglects viscosity and other fluid dynamics stuff that you need charts for, but I suspect that designing for moving water is worse than accounting for wind in most respects. |
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As long as you account for that, I don't see anything wrong with this idea. |
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Welcome to the Halfbakery. |
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+ Hi there [sdk]. Nice idea. I'd like to see an elevator it the
vunnel to get back up to the vertical ridge. |
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Good point about buoyancy cables. |
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I did some reading about deep ocean currents, and they are much slower than surface currents. Not sure how they behave in trenches, but the fluid forces may not be so bad. |
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What did you use to make such pretty calculations? |
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Where is this place that a trench is in the way of a tunnel? |
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Beaufort's Dyke, between Scotland and Ireland, is one such instance. |
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Oh the calculation where done in glorious MS Word
hehe. (the equation editor in Word 2010/2013 is
actually great) |
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About Beaufort's Dyke, that was exactly what made
me think of this idea, I was reading the Wikipedia
entry for Irish Sea fixed crossing. |
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If I have some more time maybe I'll look into the force
of ocean currents seriously. |
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Since most tunnels are likely to be between two adjacent land masses
with relatively shallow water in between, it's likely that tidal flows will
be much more significant than currents per se. |
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I'd think you'd have more trouble with (and here is where I
use made-up terms in place of proper ones I don't
remember) the shearing activity that takes place between
two layered volumes of different tempurature. Tides and
currents are largely predictable things by comparison. |
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Trains running on flat tracks fixed to solid ground develop
troublesome
oscillations at certain speeds andor certain track sections
(braking into a curve at 15mph is the most common such
scenario I've heard of). I
can easily imagine this being dramatically worse when the
track is an encapsulating non-rigid structure that can move
about on three axes (rather than conventional tracks,
which only shift in two planes, and not very much). |
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That problem may need to be addressed before we start
looking deeply into external forces. |
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A buoyant tube would have some advantages in areas of tectonic
activity, if the mooring structure had the required resilience. |
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i dinged you because viaducts are bridges carrying lots of
weight. |
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underwater you can easily solve the tranversing problem
with a zipline for tension------and if the object being
transported is very heavy you can solve it with either a
hydrofoil lifting underwater wing&propulsion system, or
simply with bouyancy control while the object is pushed or
pulled along the length of the zipline. |
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a viaduct is entirely unnecessary just make it a
zipline/single cable. |
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uh, [tesla], the poster is not suggesting an exposed
submarine. |
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Since the structure would be securely anchored at the
ends, and would be subjected to negligible vertical stress
because of the bouyancy of the tube, your main
remaining stress should be (mostly) horizontal
hydrodynamic pressure. (Assuming we can neglect the
weight of any vehicles passing through, which will
probably be a bad assumption.) |
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As this is very similar to the one-sided hydrostatic
pressure problem faced in building a concrete dam, I'd
suggest solving it in the same way: arch it into the face of
the force. |
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(With some added spoilers to compensate for any non-
horizontal component of the current vector...) |
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One problem - many of the deep-sea trenches are
trenches for a very tectonic reason. |
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