There is no immutable law requiring manhole covers to be round-why should they be round? Although some sewer covers are square or rectangular, there types are rare and are generally only found in cases where there is a need for heavy equipment to go through them. The answer to why
manhole covers are round is relatively simple, but you need to understand their use and history.
Where does the name "manhole" come from?
What exactly is a manhole cover? As its name implies-there is nothing fun here. Manholes appeared in the mid-19th century as a way to enter the sewer system. In order to adapt to the growth of the sewer system, people began to build manholes underground. Initially, the entrance to the sewer system was only large enough to allow light to come in from the hole to see if the sewage was flowing normally. Ultimately, humans need to be able to enter the sewer system.
So, to put it simply, the word "manhole" is short for a human-sized hole.
Why are manhole covers round?
So, what is the reason that the manhole covers are round instead of square? Is it just because they are always round?
Round manhole covers are more popular than the less popular square manhole covers. Is there a complicated manufacturing reason? Did the original inventor of manhole covers have some sort of grudge against right angles?
If you have ever thought that there must be some logic to it, then your intuition is correct. After all, the original design was the responsibility of the engineer! In fact, there are many reasons why the manhole cover is round, all of which are related to structure, safety and efficiency.
1. Geometry
First, there is a geometric fact that a round manhole cover cannot fall from its own opening. For example, if you have a square cover, the diagonal distance of the square length is 1.414 times the side length. This means that if you put a square cover on its opening at a diagonal angle, it will fall off easily. For more visual thinkers, imagine a children's toy with a series of shapes, such as triangles, rectangles, squares, and circles, and a bucket with the same shape on the top. The square shape can fit into a square box not only when it is aligned with the corners, but also when it is tilted. However, the circular shape must be aligned around the edges to fit.
2. Ease of movement
Depending on the size of the hole to be covered and the material of the cover, the
manhole cover may be heavy and difficult to remove. The round cover can be rolled away relatively easily.
3. Easy to install
When you want to replace the manhole cover, there is no need to worry about the alignment of the round manhole cover, it can be carried out at any angle, unlike other shapes of manhole covers. Another factor in favor of round manhole covers is that if they are bounced off by the force of a passing heavy vehicle, they are most likely to return to their original positions.
4. Economics
Believe it or not, there is another economic reason for the round manhole cover. The surface area of a round sewer cover is smaller than that of a
square cover of the same size, which means that the round cover also requires less material.
5. More geometry
Another geometric reason why the manhole cover is round is that the shape of the round manhole cover is the strongest, especially the manhole cover is only located on the shallow lip around the well head. The distance from each point on its edge to the center of the cover is the same. In many ways, each of these points has the same strength as the corners of a square or rectangular cover.
The cylindrical hole is the strongest because it can withstand the pressure of the surrounding earth. Therefore, it is easier to dig and maintain round holes. However, not all manhole covers lead directly to round holes-they usually lead to larger caves. Many underground buildings are square or rectangular because they intersect the pipe, which makes it easier to have straight, flat sides instead of round. Despite this unique situation of square or rectangular sewer covers, the other benefits of round manhole covers far outweigh this argument to the contrary.
