It has been proposed in several places that tunnels be built across the oceans. It seems to me that these dreams will be unrealized due to the vagaries of Nature; such tunnels will cross various high-earthquake rift zones, and eventually be snapped. Even a known variation on the tunnelling theme, that of letting the tunnel-tube float in the water, but tethering it to the bottom and keeping it IN the water, more than a hundred feet down, is not perfect. When the ocean floor heaves, conventional anchor blocks move, too! And so will the tethering cables, and thus also the attached tunnel. Not good! But here is how to quake-proof them:

The anchor blocks on the ocean floor should be placed on smoothed-out surfaces (not necessarily as slippery as Teflon), so if the ground under a block shifts, its mass holds it in place, not unlike the tuned-mass motion-dampers on top of various tall skyscrapers. Repair would merely consist of preparing some more seafloor in the direction the block shifted, to accommodate future horizontal shifts. Vertical shifts are a bit more problematic. Perhaps each tether cable should include a reel with extra cable, and automatic tensioning devices that take up slack when it appears (seafloor heaves up), and unreels fresh cable when needed (seafloor sinks). I'm not sure if any such tensioning devices exist for cable reels (they do exist for 10-speed bicycle chains :), but I see no reason why they couldn't.

So, now we have this nice pair of tubes stretching across the ocean, deep enough so no ship will run into them (submarines and SINKING ships excepted, although the tethering system does have some built-in "give" to it, which may ultimately be deliberately enhanced to prevent damage from exactly such incidents).

On to the vehicles! The tubes could be made of glass (thick-enough glass can be shatterproof even against collision), and the view from inside might be quite interesting. I say "might" because any vehicles in the tube will be running at extreme speed. The tubes might be evacuated for maglev cars (discussed elsewhere), or the cars themselves might be designed to USE the air in the tubes. Consider a tube that has a funnel of just-about the same size placed in it. The funnel would be the front end of a cylindrical tube-car (and another at the rear); turbines along the central axis of the car would suck air in front of the car and expell it out the expanding rear funnel (rocket nozzle), propelling the car forward AND greatly reducing air resistance! A computer-controlled circular airfoil at the edge of the funnel would force some air around the exterior of the cylindrical car, letting it "float" away from the walls of the tunnel, when moving at high speed. Also, each car could have a probocis that could be telescoped to fit in the tail of the car in front (and a tail-end ring-shaped accommodation for a nesting funnel-airfoil), making a twice-as-long car that doesn't waste energy letting air expand and be recompressed between the cars. The lengths of various trains of such cars would be quite variable. They would all have to be electric-powered, of course (via induction, probably).
-- Vernon, Jul 07 2003

mass damper http://ffden-2.phys...'s%201st%20page.htm
an explanation [Vernon, Oct 04 2004, last modified Oct 21 2004]

Trans-Oceanic Tunnel http://www.halfbake...ns-Oceanic_20Tunnel
See my third link on this idea [Shz, Oct 04 2004]

The submerged floating tunnel http://www.ita-aite...gi?d=tritu&p=p8&s=8
Here's that third link. Letting the tube hang from pontoons is portrayed, too. [Vernon, Oct 04 2004]

I think we done this one already.
-- DrCurry, Jul 07 2003


link DC?
-- po, Jul 07 2003


You would definitely want a convoluted airlock system every what, hundred miles or so? If there were damage to the tube, at least it could be contained.
-- phoenix, Jul 07 2003


Shz, I'm not surprised to see that others are working on submerged tubes. The funnel-ended tube cars are original with me, though. And, I don't recall ever seeing any mention of the specific earthquake-proofing things that I have stressed here. So I don't think I have abused anyone's intellectual priority by posting this.

dag, that's a good point about terrorists. Sometimes I think we should take all the spoiled brats in the world and give them chunks of responsibility that are totally dissociated from either privilege or authority. They BECAME spoiled by having privilege or authority, and no responsibility, see? If we cure them, then they can't grow up to become juvenile delinquents, hardened criminals, and terrorists. Nips the problem in the bud (and if they utterly refuse to be responsible, then they will never be worth anything to society, except maybe as organ donors -- which also nips the problem in the bud).

Regarding a hilly ride, those hills would have to have very shallow angles to accommodate high-speed vehicles within the bent tubes. This could be done without breaking the surface -- and I'd rather not expose the tubes at all to ship-collisions, thank you! In the long run, Murphy's Law is much more dangerous than mere terrorists!

phoenix, you have pointed out a major dilemma. High speed and suddenly-slammed emergency doors do not go together well! Still, some of what you ask for may be a natural consequence of the construction process itself. Consider that the tube would probably have to be built in sections, each of which is floated out and attached to the growing tunnel. There would TWO doors of SOME kind at each section joint! Arranging for them to be closable again, in an emergency, seems simple enough. I suppose we would have to rely on suitable communications and automated electronics to inform all vehicles approaching a sealed section to hit the brakes. This may be as easy as closing the flow of air to the turbines, because a sealed door means that air pressure will build up in front of the approaching train....
-- Vernon, Jul 08 2003


The design in that link puts the tube 150’ down, tethered to the bottom, and takes into account earth movements and ocean currents. I’m not saying it’s the same as yours. It’s just a good reference.
-- Shz, Jul 08 2003


So, take those parts out and make them a separate idea.
-- DrCurry, Jul 08 2003


Naw, I think I'll just edit this one. Watch this space!
-- Vernon, Jul 08 2003


Japan has been building under-sea tunnels in earthquake zones for years. Don't ask me how they make them safe, but they do somehow.
-- kinemojo, Oct 25 2007


[kinemojo], I think you'll find that those Japanese tunnels, such as the long one between Honshu and Hokkaido, are under ground as well as under water.
-- Vernon, Oct 25 2007



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