Quite often, when hiring a candidate for a position, they ask why sewer manholes are round. This is a very unexpected question that takes a person by surprise and he begins to think about it. This way you can quickly determine a person’s thinking, assess his level of intelligence and ability to get out of difficult situations. If a person hesitates, thinks about it for a long time and gives a completely illogical and incorrect answer, then one can judge his inability to think creatively and quickly. But what's really interesting is why the sewer manholes are round and not square. There are different theories and answers. Let's try to figure them out.
Manhole cover
The cover is an integral part of the manhole hatch, which must be present. In addition, it should be comfortable and ergonomic, and should not rattle when a car wheel hits it. It also has a small hole through which you can check the gas contamination of the well.
With all this, the lid is most often made of cast iron and is very heavy. Its large weight is justified by the difficulty of theft, but it is precisely because of such a large weight that it is often stolen for subsequent scrap metal. And although the law prohibits the acceptance of sewer manholes at scrap metal collection points, this does not stop thieves. Some people use them in everyday life for various purposes.
However, this is not about that now. In most countries, the lids are indeed round, but there are exceptions. In some states of the USA and even in India they are made in the form of squares and triangles. Therefore, it cannot be said that all manhole covers are round. Why is the round shape most common? As mentioned above, there are different versions.
Logical version
The very first version explains the shape of the lids by economy. The fact is that it is the round shape that, at minimal cost, allows you to create a hole that a person can easily crawl through. For example, for a person to freely enter the well through a square hatch, the hole would have to be made a little larger in area. Consequently, when making a hatch for such a hole, more metal would be spent, and this is not economically viable. It is believed that the production of round hatches is 40% more profitable compared to the production of square ones, and on a large scale this is a fairly respectable figure.
Due to the round shape, the lids do not fall down
The second version, which explains why sewer manholes are round, is that this shape prevents the manhole from falling down. That is, under no circumstances, no matter how hard anyone tries, will he be able to push the lid into the well itself. But a square manhole cover can fall into the well if you try to insert it with its edge diagonally across the hole.
It is also believed that the round shape has a good feature - it more evenly distributes the load when a car hits it. Consequently, this allows the section size (thickness) to be slightly reduced, which ultimately leads to additional cost savings.
For a round well - a round lid
However, it is strange to even ask why sewer manholes are round, because the well itself is round, so when developing the covers, no one even thought about using a square shape. Moreover, if you need to quickly move the round hatch cover from the well, you can simply roll it on its edge, which can be done even by one person. But rolling a square hatch will not work - it must either be transported or carried by two or even three people. However, some lids have special “antennae” that make it impossible to roll them edgewise.
It is also believed that opening a round manhole cover is easier due to the fact that any point on its circumference is also a point of stress concentration. As for square lids, there are only two similar points - the corners of one of the sides.
It just happened that way
In general, no one knows why sewer manholes are round. Few people think about this, but looking for an answer to this question is simply stupid. It's like asking why curbs have a rectangular cross-section. There is no definite answer to this question, because when the first sewer wells appeared, no one thought about making them in other shapes. It just happened that way, and all attempts to explain why the hatches are round are, to put it mildly, far-fetched. The only more or less logical option is the inability to drop the hatch into the well itself. This is possible with a square lid, since the diagonal length of the lid itself will be greater than the length of the side. This makes sense, but even this explanation does not suit many.
Other forms
Note that hatches are not always round. IN different countries forms can be different. In India, triangular shapes are common, and in some countries they can be a generally vague geometric figure. Square shapes are not uncommon in the USA and other American countries. There are even hatches with eight corners, and very rarely there are models in the shape of a diamond or semicircles.
But it is worth recognizing that most often they are round. This form is the most popular, comfortable and ergonomic.
Conclusion
So, we figured out why the hatches are round. You can answer this question in different ways. If you really want to get really boring, you can calculate how much metal is needed to make a square lid for a hole that a person could easily fit into. The resulting value must then be compared with the weight of metal required to make the cover for the round hole. With the same cross-section of metal, it turns out that more metal will be needed for a square hatch due to the presence of corners in the square.
You can also calculate how evenly the forces are distributed when a car wheel hits the hatch. It turns out that the loads are distributed more evenly along the entire perimeter of the circle. This is not the case with a square or triangle.
In general, now you know why sewer manholes are usually round, and you understand what you need to answer if you are suddenly asked about this at an interview. Most likely, this is the only case where such information can help. However, if we are talking about an interview, then it is not at all necessary to answer correctly. You can answer with a joke or generally say that manholes from sewer wells are not always round, it’s just customary in our country. Sometimes even the person who asks such a stupid question doesn’t know why hatches are round in the first place. However, you now know the answer for sure. Despite many good versions, the most logical and plausible version seems to be the one with the shape of the lid, because of which it simply cannot fit into the sewer hole.
A familiar, familiar detail of the urban landscape are sewer manhole covers, which are round in shape almost everywhere, in all countries of the world.
Why round – we will try to answer this question in detail.
Safety
The manhole cover of the sewer well is a massive piece of cast iron. It weighs more than 50 kilograms, and the weight of hatches located on the roadway exceeds 78 kilograms.
This is not surprising, because a manhole cover located on the sidewalk of the street must withstand a load of 12 tons, and a manhole cover lying on the road must withstand a load of as much as 25 tons. This weight is due to the thickness of the cover, calculated taking into account the given load and the strength of the cast iron.
Now imagine the following situation: the manhole cover is open and lies next to the hatch, and below, people are working in the well. If someone accidentally moves the round lid, then in the worst case they will simply close the hatch. In this case, a rectangular or square lid can fall into a hole directly on the heads of the workers, because the diagonal of a square or rectangle is always larger than any of its sides. Therefore, the round shape of the lid is the safest in in this case.
Strength
Engineers have long known that round objects are much stronger than square ones. The sewer hatch is not only round, but also slightly convex in the middle: this shape provides the greatest resistance to mechanical load directed from above.
Internal stresses in a hatch of this shape are evenly distributed over the metal, while in square, rectangular and any other covers, under the influence of a load, the stresses are distributed unevenly, which leads to faster wear and, consequently, more frequent replacement of covers.
In addition, we should not forget that cast iron is a rather fragile material, and if you drop a rectangular lid, a corner may well break off. To crack a round manhole cover, you will have to put in a lot more effort. 
Judging by the fact that almost all the lids have been lying intact for decades (and some for more than a hundred years), in normal conditions It is almost impossible to damage the round cover.
Metal saving
Why is the round shape of hatches more optimal in terms of saving metal? With the same length of the perimeter of round and rectangular hatches, the area of the circle is always greater than the area of the rectangle or any other geometric figure.
If we translate this into economic indicators, it turns out that a circle is the most profitable hatch shape, since it requires much less cast iron for the cover (saving up to forty percent) than for a rectangular cover.
The optimal ratio of perimeter length to area makes it necessary to make round hatches not only for sewer wells, but also in much more serious structures - for example, between compartments of submarines or spaceships. Round hatches are more economical and can withstand greater loads than any other shape.
Convenience of work
A round manhole cover is much more convenient when carrying out repair or maintenance work. If a rectangular lid needs to be lifted in order to be moved over a certain distance, which will require at least two adult men, then a round lid can be easily rolled by placing it on its edge, and this task can be completed alone.
And in order to fit the heavy cover into place, you do not need to rotate it, adjusting it to the configuration of the hole. The round lid will fall into place in any case, no matter which side you lay it on. 
So, there are more than enough reasons why you need to make the manhole cover round.
Many people have come across the question of why sewer manholes are round in shape. Most have heard it during job interviews. In this way, “cunning” HR managers test the general erudition and ability for creative thinking of potential employees.
This question is also often used in various competitions and quizzes. If you study the design of sewer hatches, the answer to the question will become obvious and quite understandable. This is what we'll do.
Sewer hatch installation
A sewer well usually consists of a shaft and a working room, and the hatch serves as a cover. Workroom are arranged and located depending on the type of communications being served and the requirements for their operation. The depth of the shaft and the size of the room also depend on this.
- Typically the height of the room is 1.8 meters, but it can be more or less. The main criterion for its determination is the depth of communications. The length of the shaft directly depends on the depth of the room. Typically the shaft is round in shape and has a diameter of 0.7 meters. The shaft must have a ladder so that the worker can go down into the room. The material used for shaft construction is usually brick or concrete.
- A cover on the sewer hatch is necessary to prevent foreign objects and people from entering the mine. The round shape prevents the lid from falling into the shaft if someone steps on it, which means it protects against accidents. This is the most important reason why the shape of sewer manholes is made round.
- Also the lids have enough large mass, and sometimes this also raises questions. This fact can also be easily explained. Very often, sewer manholes are located on the roadway and when driving, the car wheels hit the cover. If the lid were light, it would easily flip over, opening the shaft and creating the possibility of accidents. To avoid this, the lids are cast from cast iron, which is considered one of the heaviest metals.
- The surface of the lid usually has raised stripes, letters, or other designs or images. This was also not done by chance. The ribbed surface prevents slipping and increases the adhesion strength of car tires and pedestrian soles to the surface of the hatch. There are flat lids, and sometimes they are curved in the middle, but you will never see concave ones anywhere.
Cable duct wells usually have two covers at once - a protective cover and a shut-off cover.
The protective one is on top. There is an additional lock on the locking cover, which prevents unauthorized persons from entering the shaft to steal the cable. These lids are lighter than regular ones because they are made of steel.
Also, sewer manholes can be installed in gas, heat, water and other wells utility networks, as well as storm drains.
Each of them is designed to ensure that no unauthorized person or animal accidentally or intentionally enters a sewer well or mine or gains unhindered access to underground utilities.
Types of sewer manholes
Sewer hatches can be divided into several types depending on the design, the material from which the hatch is made, and the type of communications that it covers. Sewage hatches may block water waste systems, cable (electrical or telephone), storm drainage systems.
Depending on the material used in manufacturing, cast iron, plastic, composite, concrete, reinforced concrete and rubber hatches, as well as hatches made of a polymer-sand mixture, can be distinguished.
Helpful information ! Each material has its own pros and cons, taking into account which you can choose best option for a certain situation. But anyway traditional option is a sewer manhole made of gray or high-strength cast iron. This material has high strength, is resistant to mechanical stress of various types, is independent of weather conditions, and its service life exceeds the shelf life of all other materials.
Safety of sewer manholes
The main purpose of making the sewer manhole round is to ensure the safety of the population. Unfortunately, cases of an adult or child falling into an open sewer shaft are not that rare. If the mine is shallow, then this can result in one or more fractures, but greater depth can even lead to death.
Common reasons Such falls include theft of a manhole cover.
Nowadays, many people, walking down the street, are distracted by talking on a mobile phone or writing SMS messages, sometimes so carried away that they forget to look at their feet. This kind of absent-mindedness leads to accidents.
Also, a car can get caught in an open hatch, which at best will lead to minor damage to the car, and at worst, to injuries to passengers. Those who like to ride other types of transport - scooters, motorcycles, mopeds, bicycles, rollerblades or skateboards - are also at risk. Falling into a hatch at high speed can result in serious injury.
Fun facts about sewer manholes
If the manhole was installed long ago, opening it can be a serious problem. In this case, specialists weld a metal handle to the hatch from above, open the hatch, perform the necessary operations, close it, and then cut off the handle.
Also, hatches with existing holes into which you can insert a hook and thus pull out the cover have long been put into production.
But such hatches cannot be used when closing electrical, telephone and cable networks. This is because water can get into the holes due to rain or melting snow, which can damage the network and negatively affect the operation of the entire system.
The issue regarding the excessive mass of sewer manholes should also be explained.
This weight is given to the lids specifically in order to make it difficult and sometimes even prevent their theft. The fact is that free metal has always attracted those who like to make money at the expense of the state. Thus, in the last decade of the twentieth century, several thousand sewer manhole covers were stolen on the territory of the Soviet Union. Thieves sold them for scrap metal, thereby earning significant money.
Helpful information! To avoid theft, wooden shields, plastic hatches or concrete circles are currently used to cover the main cover on top. Lids fastened with metal hinges have also become widespread. They cannot simply be removed and carried away; special equipment will have to be used, which will complicate the theft process.
Also, the hatches are made so massive that teenagers do not play in the sewers or use them for other, less decent things.
There are several other explanations for why sewer manholes are round.
- Firstly, this shape makes it easier to transport. The hatches are quite heavy and to move a lid, for example, a square one, you need to use the strength of one or even two adult men. The round lid can easily be rolled along the ground by any teenager and over any distance.
- Secondly, there are no problems when installing the cover. It is unlikely that anyone will have questions about its location in the well hatch. The only mistake here could be installing it the wrong way up, but this is not very critical for operation.
- Well, and thirdly, less material is used for the production of round products.
Civilization began to take shape only when man invented the sewer system. The first organized sewage systems began to appear in the megacities of Ancient Egypt; in Ancient Greece and Rome they were improved and even then, in fact, they received the architecture that we have today, if you look into any sewer hatch.
New collection of hatches
For the common man, the theater starts from nowhere, and the city sewer system, power lines, communication cables, storm drains all start from the manhole. Today we will focus on hatches in the literal sense of the word, we will figure out what they are actually made of, why the sewer hatch is round and look at photos of the most interesting hatches.
Yes, hatches can be interesting too. There is a certain type of collector who collects interesting hatches. Of course, we do not welcome theft of municipal property, but there are also ardent fans of this type of collecting who will do anything to steal a historical or rare hatch. We present a selection of such sewer manholes on the page. Those that have not yet been stolen.
Features of the installation of underground communications
We rarely think about how the city sewerage system, drainage systems, how communication lines and powerful power cables are laid. This is a rather complex engineering system that has its own laws and unshakable rules. When designing a sewerage system, they take into account not only geodetic data, but also the communications system, which was laid perhaps several centuries ago.
Urban project sewer system contains a lot of information that is summarized in one document. A lot of factors are taken into account:
It often turns out that one hatch can work both for servicing communication channels and for water supply, heating and sewerage systems, which greatly complicates the process of repair and operation.
Pipeline routing rules
If we're talking about sewer pipes, then their laying, or in engineering terms, routing, requires compliance with the most modern standards and rules, which are often updated in connection with the expansion of the city’s infrastructure. Here are just the basic laws of pipe laying:
Any sewer manhole consists of a neck ring and the manhole cover itself. The diameter of the neck can be from 600 to 1500 mm, but there are hatches up to two meters in diameter. The size of the hatch directly depends on the inspection chamber in which preventive work and pipeline repairs are carried out.
Why are all hatches round?
The immediate task of the hatch, that is, its cover, is to protect the inspection chamber from dirt and dust, as well as to prevent foreign objects from entering there. And, of course, hatches are installed for the safety of passers-by or vehicles, since inspection cameras are most often located either on highways or under pedestrian paths.
The classic sewer hatch is round and made of cast iron. The shape of the hatch is determined primarily by the following points: 
And it’s somehow more common to see roads and sidewalks with round hatches, which may not necessarily be metal. In those areas where heavy vehicles are not expected to pass through, plastic hatches are now being installed that can withstand loads of up to 5-8 tons.
Perhaps the hatches have some other secrets, but we have answered the main question, which has already become a classic, and admired the hatches, so the conversation can be considered completed. Walk on hatches carefully!
Many people are interested in why sewer manholes are made round, but not everyone knows that this shape is considered the most practical. It is safer to use round lids, and at the production stage of products, metal is saved. Of course, in addition to round ones, there are hatches of other shapes on city streets, for example, square ones, but they are quite rare. This is explained by a whole series of factors.
Security Considerations
Despite their small dimensions, the lids weigh about 50 kilograms, because they are made of cast iron. And the weight of products located on the roadway exceeds 78 kilograms - after all, they must withstand the weight of passing cars. According to the rules, hatches located on sidewalks must carry loads of up to 12 tons, and those intended for installation on the road - up to 25 tons.
Given the significant weight of the covers, it is very important to follow safety rules when working in a sewer well. If the product falls through the hatch onto the heads of the workers, tragedy cannot be avoided. Fortunately, the round lids are designed to never fall down the well. Products shaped like a square or rectangle can easily fall off, because their diagonals are always larger than any of the sides.
Ease of use
Considering the large weight of cast iron covers, dismantling them is quite difficult, especially if they are square. To move such hatches from place to place, you will need several adults. Round lids are much easier to handle because they can be rolled on an edge. You can cope with this task even alone.
The round lid does not need to be rotated, trying to adjust it to the shape of the hole. It will take the desired position no matter which side you place it on.
Increased strength
Since the covers that are used to protect engineering systems, are subjected to heavy loads during operation, care must be taken to ensure that these products have improved strength indicators. The easiest way to achieve this is to make the hatch round, because products of this shape have improved strength compared to square ones.
Photo: standard sewer manhole
In addition, if you carefully examine the structure of the hatch, you will notice that towards the middle of the circle it is slightly convex. This is not an accident: this shape ensures the most uniform distribution of internal stress in the product. Rectangular covers do not have this property; the loads in them are distributed unevenly and lead to increased wear of the metal.
Cast iron is a brittle material, so cracks and chips may appear on its surface as a result of mechanical stress. Round hatches are made in such a way as to prevent the destruction of the metal: it is much more difficult to break off a piece from them than from square or rectangular-shaped products.
The load concentration points of a round hatch are evenly distributed around the entire circumference. With square products, stress is concentrated only in the corners, and this is very risky, because you cannot transfer the entire load to just one part of the part.
Economic expediency
In addition to improved consumer properties, the round shape saves metal. With the same perimeter length, a circle always has an area greater than that of a rectangle. Thus, the production of round hatches is economically feasible, because savings on materials can reach 30%. It turns out that instead of three square lids, four round ones can be made at the same cast iron consumption.
Considering the low cost of round manholes, on a city scale, the savings on the installation of sewer wells look impressive. In addition, round covers are widely used to protect other communication systems, such as waste pipelines, gas pipes or underground electrical networks.
The advantages of round hatches include not only metal savings, but also a very small percentage of rejection. Reducing the number of reference lengths is the key to a low probability of errors leading to the appearance of various defects.
Photo: open sewer manhole operating on the principle of doors Who is responsible for the hatches
Sometimes hatches are equipped with hinges - this is done in order to avoid theft, which has become especially noticeable in the last two decades. Cast iron products are in demand at metal collection points. Additionally, the hatches can be locked - in this case they resemble a door.
Most sewer wells, including their covers, are municipally owned, although some may be owned by legal entities and apartment buildings. If an object is ownerless, at the request of local government representatives, it is registered with the body that registers property rights. Then, if the owner is not found, the hatch is transferred to the balance of one of the specialized companies.
