Welcome to European Tribune. It's gone a bit quiet around here these days, but it's still going.
Sorry for nitpicking, but
  1. cement is actually rather light, c. 1.5 t/m³;
  2. concrete is more dense, up to 2.5 t/m³;
  3. however, methinks the buoyant tunnel would be made of steel, which is much more dense than concrete: 7.8 t/m³.

*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Tue Dec 22nd, 2009 at 06:24:42 PM EST
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