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-A round manhole cover cannot fall through its circular opening, where as 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.
Quote -Human beings have a roughly circular cross-section. ...sorry, you cannot view external links. To see them, please
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-Human beings have a roughly circular cross-section.
[Isn't the politically correct term "personhole" ]
Isn't the politically correct term "personhole
Some better suggestions ...
Thieves steal manhole covers to cash in on scrap metalAug 14 2008 The rocketing price of scrap metal has led to 220 manhole covers being stolen in four nights across Warwickshire. The Local Government Association said an estimated 50,000 drain covers had been stolen this year, with thieves usually striking at night, costing councils an estimated £1.5m this year and leaving drainage systems exposed. In the past few weeks, 20 covers were stolen on one day in Northampton and Accrington and 42 were taken in 10 days in Slough, while more than 250 covers have been stolen in Surrey since April. Councils have to pay at least £300 to replace a drain cover.