Why are manhole covers round?

Self explanatory title.

5 Answers

  • 10 years ago
    Favourite answer

    Reasons for the shape include:

    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 hole. (A Reuleaux triangle or other curve of constant width would also serve this purpose, but round covers are much easier to manufacture. The existence of a "lip" holding up the lid means that the underlying hole is smaller than the cover, so that other shapes might suffice.)

    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.

    Similarly, it is easier to dig a circular hole and thus the cover is also circular.

    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 a lathe.

    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 a cover had corners and were bent that would create a protruding point that could puncture tires.

    Most manhole covers are made by a few large companies. A different shape would have to be custom made

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  • 10 years ago

    Because they are not all round?


    In England it is compulsory that every manhole cover has at least a mass of 50kg, so sewage doesn't explode everywhere x;.

    http://img.groundspeak.com/waymarking/96f3eecd-429... I FOUND A TRIANGLE MANHOLE COVER \O/

    There is no mechanical explanation why most are round, other than it's conveniant to the shape of the piping. But a circle can fit inside a square.

    Statistics here, to all the one above -

    1in2 manhole covers in the UK are square or rectangular. Now that's a lot of manhole covers gone wrong? Circular covers won't make it easy for someone to get down the whole because the cover has to be taken off, and the pipe beneath will be circular no matter what shape its cover. Rectangular and square manhole covers are considerably bigger than circular, so your 'falling down manhole-cover' syndrome won't happen. \o/ Rectangular & Square manhole covers.

    The width of a square would be greater than the diameter of a circle for manhole covers. or it would fall down when its laying flat.

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  • 10 years ago

    Manholes cover should be round because, covers of other shapes can fall inside the manhole if inserted diagonally.

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  • Anonymous
    10 years ago

    Because the pipes that are under the manholes are round?

    Round objects are also easy to turn.

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  • 10 years ago

    If they were square they could fall down the hole, because the diagonal distance between oppisite corners is greater than the sides.. ill try draw it..








    hmm... slashes arnt on big enough angle... so looks crap, haha.

    but you get the point...

    imagine a triangle... hypotenuse is bigger then other two sides in right angle triangle, and a square is just two right angle triangles...

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