The hole under the cover is round, because the cylinder can bear the pressure of the surrounding land best. Moreover, there should be enough space for a person to pass through the sewer outlet hole, and the cross section of the person climbing down the ladder is basically round, so the circle naturally becomes the shape of the sewer outlet hole.
Moreover, the diagonal of the square is longer than the side, and it is easy to fall into the well. Why is the manhole cover of the sewer round?
This question is a question in Microsoft interview, and the specific answer is as follows:
Interviewer: Now we're going to ask a question to see your creative thinking ability. Don't think too much, describe your thoughts with common sense of daily life. The question is: Why is the manhole cover of the sewer round? Fanman: They are not round. Some are square. There are indeed some round manhole covers, but I have also seen square and rectangular ones. Reporter: But we only consider circular manhole covers. Why are they round? Fanman: If we only consider circles, then they are naturally round, which is a repetition in itself. Reporter: I mean, why are there round manhole covers? Is there any special significance in designing the manhole cover into a circle? Fanman: It has special significance. When the hole to be covered is circular, the cover is usually circular. It is the easiest way to cover the round hole with a round cover. Interviewer: Can you think of any advantages of round manhole covers over square manhole covers? Fanman: Before answering this question, we need to see what's under the lid. The hole under the cover is round, because the cylinder can bear the pressure of the surrounding land best. Moreover, the manhole is to leave enough space for a person to pass, and the cross section of a person climbing down the ladder is basically round. So the circle naturally becomes the shape of the sewer access hole. The round manhole cover is just to cover the round hole. Reporter: Do you think there are security considerations? I mean, will the square manhole cover fall in and cause personal injury? Fanman: Not likely. Sometimes you can see the square cover on some square holes. This kind of cover is bigger than the entrance and has rungs around it. Usually this kind of cover is made of metal and heavy. We can imagine a square hole two feet wide and a track 1 to 1.5 inches wide. In order to let the manhole cover fall in, you need to lift one end, then rotate it 30 degrees, so that it will not be blocked by the crosspiece, then make the manhole cover at a 45-degree angle with the horizon, and then shift the center of gravity enough to let the manhole cover fall. Yes, it is possible for the manhole cover to fall off, but it is very unlikely. As long as the person in charge of opening the manhole cover has a little training, he won't make such a mistake. From the engineering point of view, the shape of the manhole cover depends entirely on the shape of the hole it covers. Interviewer (face is reluctant): Excuse me; I need to talk to management about something. (Leaving the room) (10 minutes later, the interviewer came back. Interviewer: We suggest that you work in the sales department at once.