Comment by contravariant
9 years ago
>But there's no engineering reason why a hole in the ground can't happen.
Well, unless you count damage to whatever happens to be in the way of the tunnel and buildings on top of tunnel. This might be more of a problem in Europe than in the U.S. though.
Look at the Seattle viaduct replacement problem. Bertha came to a standstill for years due to engineers not taking care of a well pipe they thought they removed.