Manholes are typically round it is impossible for a round manhole to fall through its circular opening. A square manhole cover would fall in you inserted it diagonally in the hole. Again, round covers are easier to manufacture
1 year ago
Last edited at 9:01PM on 2/27/2013
You could pickup a square or rectangular one, rotate it, and then drop it in. No matter which way you orient a disk will it not fall through assuming the ground radius is lesser than the disk radius. Just my guess.