Have someone tried this method in other place? Does it work when the walls have sharp edges, sharps turns, and there are water currents flowing at high speed around it? (I guess NASA might be using that method inside a pool.)

What does it mean "glue 2 sides together"? Underwater? For 800m? Completely air and water tight?

Does untrained people be "confortable" to craw in a dark tunnel for 800m or the children would have freak out in the middle?