Why are manhole covers round?

Question

D.G. Fox · Accepted Answer

There are atleast three reasons manhole covers are round.

1. A round cover can not fall into the hole.
2. A heavy round cover can be easily moved by rolling it on its edge.
3. A round cover can be easily centered and aligned when being replaced.

I'm certain there would be other possible answers, such as its easier for a person entering the manhole at any angle with round hole and cover....etc etc

Anonymous · Answer

Oh God. Not this stupid question again? What does it test besides whether you've already heard this question?

Mark J. · Answer

The cover shape has nothing to do with the answer. Below the lid is a manhole neck that can be 20' deep. It is round concrete because this offers the most strength for the buck (so people can safely climb in and out.) A round metal reduction "ring" is then placed over the round neck and then embedded in asphalt or earth. While this ring (cast iron) could be cast to accept any shaped lid, I suppose, a round lid is the strongest and most load efficient for the cast iron ring.

anonymous · Answer

Google shouldn't be THIS MUCH STUPID to ask this sort of brain teasers!

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