Hi lucyfur,
Manhole covers are round so that the cover cannot fall through the
hole. If the cover is not a circle, then there are at least two
lengths across that have different measurements and the smaller width
can fit through the direction of the longer width. For example, a
square manhole cover can fall through the square hole along its
diagonal.
"Manholes, which interconnect underground sewerage pipes, and serve as
a point of entry for cleaning the pipes, are located at every major
sewer pipe junction, and are capped with round manhole covers. The
reason for the circular construction of these covers is, quite simply,
that covers of any other shape would fall through the manholes by
virtue of their varying diameters. Circular manhole covers do not vary
in width, or in diameter, as is the case with these other shapes, thus
remaining in place despite the street traffic running roughshod over
them.
Manufacturers craft the manhole covers together with the smaller sized
lip, upon which they rest, at the same time to ensure a tightly sealed
fit. Additionally, the manufacture of circular manhole covers is
easier and more accurate than the manufacture of covers of any other
shape. Lastly, round manhole covers, once removed, require less
lifting and less manpower, as their shape allows them to be rolled."
Cool Quiz: manholes
http://www.coolquiz.com/trivia/explain/docs/manholes.asp
Improved Construction Methods
http://www.improvedconstructionmethods.com/why_are_manholes_round.htm
Some articles regarding this:
The telegraph: Three sides to city?s manhole story
http://www.drainspotting.com/mirror/nhtelegraph-2003-11-26/
The Straight Dope
http://www.straightdope.com/classics/a1_247a.html
Sniptools
http://sniptools.com/vault/why-are-manhole-covers-round-and-other-trivia-about-the-pesky-drains-covers.htm
Search criteria:
"manhole covers" round "not square"
I hope this helps. If you have any questions regarding my answer
please don't hesitate to ask before rating it.
Best wishes,
rainbow-ga |
