Why are manhole pits circle?

Question

Why are manhole pits circle?

Answer 1

to facilitate entry and exit.

Answer 2

A round manhole cover cannot fall through its circular opening, whereas a square manhole cover may fall in if it were inserted diagonally in the aperture (A Reuleaux triangle or other curve of constant width would also serve this purpose, but round covers are much easier to manufacture.)

Round tubes are the strongest and most material-efficient shape against the compression of the earth around them, and so it is natural that the cover of a round tube assume a circular shape.

The bearing surfaces of manhole frames and covers are machined to assure flatness and prevent them from becoming dislodged by traffic. Round castings are much easier to machine using horizontal boring mills.

Circular covers do not need to be rotated to align them when covering a circular manhole.

Human beings have a roughly circular cross-section.

A round manhole cover can be more easily moved by being rolled.

If an automobile rolls over a dislodged manhole of another shape, the sharp corners could puncture the automobile's tire, whereas a circle doesn't have corners.

It's easier to dig a circular hole.

Tradition

Aesthetics

Supply. Most manhole covers are made by a few large companies. If you want a different shape, you will have to pay more to have them custom-made or you will have to make them yourself.

I know, I took all the fun out of your psychological assessment... : )

Answer 3

because it always fits, unlike square and rectangle manholes

Answer 4

because, no matter how u place the cover on, it wont fall down into the hole.

Answer 5

Because any other shape, and the lid could fall down in there when putting it back in place...the covers have o be heavy in order to prevent them from flipping up when walked or driven over. So you dont exactly want someone having to precisely put them back in place... its easier to slide them back into place.

A circle is the only shape that is impossible for the cover to  fall in the hole. Square, Rectangle, Triangle, Oval... they can all be turned to where the cover can fall into the hole.. but not a circle.

Also, man hole pits are a pipe, leading into a pipe... which is round.

Answer 6

They are square also. But a majority of them are circle.

I think its easy to get down into it keeping its opening small and maybe it can also be by convention. Its been carried on through ages

Answer 7

beause a cylindrical tunnel leading into the sewers is less likely to cave in on itself as a square, as circles are stronger and triangles of the same area wouldn't fit the workers