Why is the shape of the manhole is cirlcle?
Answer:
*"You take your squares, for instance. A square cover you can tip up on edge and drop through the hole on the diagonal, if you follow me. Similarly with ovals. A circular hole, however, will defy the most determined efforts in this regard. (Bear in mind that there's a lip around the inside of the manhole that the cover rests on; this effectively makes the diameter of the manhole an inch or so less than that of the cover.) This means manholes are one of the few things in the universe that are absolutely goofproof."
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*1. So that they don't fall into their holes.
2. So that they may be rolled for transportation.
3. It is aesthetically pleasing.
4. It saves architects the trouble of designing them.
5. They don't get damaged easily.
6. Circular covers are easier to manufacture than other shapes.
7. So that they open on all sides (since they don't technically have sides on their edges).
8. Being public property, these covers may pose a safety hazard if they have sharp or uneven edges, especially to sewage maintenance personnel.
9. So that in a hot day, the cover expands evenly and does not cause cracks in the tarmac due to uneven expansion.
10. To answer this question, it is like asking why the manhole is circular, since a cover has to conform to the shape of its hole. The manhole is circular as it allows the majority of sewage maintenance personnel access into the sewage system, regardless of body size. Also, the lack of edges is safer for these people who might inadvertently hit their heads on a seemingly innocuous edge.
*Please visit following link and you will come across all probable reasons:
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One answer is they're easier to move (by rolling) than square ones. Another is that they can't easily fall into a manhole by slipping down through the longer diagonal in the middle.
Actually, not all manholes are circular. Occasionally you'll see a square one, but they are very nearly all circular and the reason is that a circular disk cannot be turned in a way that would allow it to fall into the hole, whereas you can turn a square one in a way that it will fit inside the hole. The reason you don't want it to fall in the hole is that it might fall on someone who is working in there or, secondarily, it might fall in if some kind of rare occurrence happens like an overpressure that blows it up into the air a few inches.
Incidentally, I've never seen anyone roll a manhole cover.
Because when the heavr cover is being removed or replaced, it cannot fall into the hole. An oval or square cover can fall in, but a round one can't.
a circle has no edges...that makes it easy for the person going in the manhole to close it up...thus preventing their fingers being ran over by a runaway truck
The steel manhole is much harder than the concrete or asphalt street. When a 15 thousand pound truck axle rolls across the manhole cover its under a lot of force very breifly. When the tire rolls away its suddenly free of force. If the hole and cover were square it would not be long until you would see cracking and pot holes at the four corners of a square one. A round one might last a decade. A square one might not last a year. Also down below the street you have economics going on. The city that has to tax people to build the hole can be good stewards with the material. A circular shape evelops the same area as a square but with less perimeter and less material cost.
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