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  1. boats and submarines?  I don't know of any archemdies tunnel in existence, but there are plenty of structures in the ocean with the same principle - oil platforms often use buoyant legs to reduce the total strength requirements.

  2. Displacement of water: if the tunnel is say 10m in diameter it displaces roughly 80m^3 per metre, which is much much more than any train weights (that would be a lot more than 80tonne axle load!), even with the tunnel itself weighing a few tonnes per metre there is far more lift available than any train would require.

  3. I think so.  We can hypothesize various simple strategies: double wall with inner pair of train tubes and outer service tube, fast closing doors every few km, automatic breach detection and autopilot system (if a breach is detected behind, accellerate away, before, decelerate and reverse at maximum rate), automatic detactment and floating in the case of severance, safety tanks where people can climb in and float to safety. etc.
by njh on Tue Dec 22nd, 2009 at 05:11:52 PM EST
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