All hatches of manholes are closed with round hatches, and this is done all over the world. The question involuntarily arises as to why the sewer manhole is made round.
This question has already become a playful puzzle, it comes to curiosities when people try to answer it. And the answer to it lies on the very surface, you just need to know about its device and where and for what it is used.
Logical explanation of the shape of the hatch
So why are sewer manholes made exactly round, and not, for example, square, rectangular or triangular. The answer is simple - all because no matter how you twist it, it will never fall into the well and cause trouble there, for example, hitting a person working there or breaking through.
A cover of a different shape, for example, a square one, can move due to vibration and slip into the well at an angle. This is due to the fact that the square has a diagonal larger than its sides, and the circle has one radius (whatever one may say).
Another option that should not be rejected is that the round shape reduces the internal forces that may arise during its installation. Thus, savings can be made by producing thinner caps.
Video: Why manholes are round
In addition, the round lid is easier to transport for one person. It can be rolled to the place, and the square one will have to be carried with assistants.
The above explanations show that elementary practicality and economy influenced the choice of the shape of the sewer manhole.
Manhole device
Sewer hatches are installed on top of manholes, which are divided into several types, depending on the type of communications:
- Drainage systems.
- Storm sewers.
- Electrical networks.
The observation well is arranged as follows:
- work space;
- Mine;
- Lid.
The size of the working room can be different, it all depends on the type of communication for which it is intended. Its depth also depends on the depth of the network, standard height considered - 1.8 meters.
The shaft is made round, with a diameter of 70 centimeters. The walls are laid out from concrete rings or brick and equipped with a ladder.
The hatch, for security purposes and to prevent cluttering of the mine and the working room, is closed with a lid. Lids, until recently, were made only of cast iron, so they have a fairly solid weight.
The large mass of the structure is necessary condition, as this helps to prevent its spontaneous movement due to vibration from the movement of cars. The weight of cast iron hatches depends on their design and size.
So, for example, the mass of the hatch cover alone of the brand T (S250) is 53 kg, TM (S 250) is 78 kg, TM (D400) is 45 kg. So, these are quite heavy items that are not easy to lift.
There are ribs on the surface of the lid. This is done to increase strength and better adhesion to car tires and soles of pedestrians. The lid can be flat or convex.
What material are hatches made of?
In the manufacture of sewer manholes can be used different material. It could be:
- Cast iron.
- Concrete.
- Reinforced concrete.
- Polymer-sand mixture.
- Composite material.
- Rubber.
Previously, preference was given to cast-iron hatches, which were considered the most durable and reliable. Today, more often you can find hatches made of other materials - plastic, rubber or composite. On the one hand, they are much cheaper, and on the other hand, they are not inferior in quality to their predecessors.
In the 90s, a “boom” swept across Russia associated with the theft of cast-iron covers from sewer manholes. Therefore, the manufacturer and operating companies have gradually switched to hatches made of other materials that cannot be scrapped.
Conclusion
Sewer hatches of a round shape are more practical, technologically advanced and have long term operation. Such models are resistant to temperature extremes. That is why this form was chosen for them.
Video: QUESTION - ANSWER No. 11 Why manhole covers are round
Access to underground utilities is reliably protected with manhole covers. Made of cast iron, they are not such a tasty prey for thieves, and special holes do not allow them to be opened. To understand why the hatches are round, you need to have the mind of a practitioner.
What are sewer manholes for?
A manhole cover that opens the way down can be called a means of prevention. It is heavy circles that prevent many injuries and deaths. You can safely stand on them without fear of falling. Only those hatches are dangerous if the cover is missing or has a shape that does not look like a circle.
Currently, caps of a different shape are extremely rare.
Why are they round
The main advantages of this form:
- safety - the circle does not fall inward, no matter how you turn it, it will not hit the one below and will not drop the one standing above;
- savings - less cast iron is used for a round shape than for a square one, since the moment of stress under load on the circle is less and the cover can be made thinner;
- convenience - it is physically easier to open such a lid, this property is also used in the form of cans for canned food.
And another plus in the treasury of the economy of production - there are few defective products. This is due to the smaller number of reference lengths for the circle.
In addition, the round shape reacts less to temperature changes and therefore lasts longer.
In the absence of a cover, the hatch must be fenced and marked with warning signs. If only they had a different shape
Imagine that a manhole cover is square, triangular, or rectangular. Now let's try to move this cast-iron product from place to place. The circle will roll like a wheel, which is not the case with angled shapes.
A square cover is only safe when its side length exceeds the diameter of the round hole. This entails an increase in the consumption of material for manufacturing, which is inappropriate. If the well itself is square, then you just need to turn the lid a little - and it will fall inward, losing its protective functions. Therefore, it is not difficult to guess why hatches are made round and not square.
Manhole covers usually weigh 50 kg or more so that they cannot be moved from the manhole even in heavy traffic. In the US city of Nashua, New Hampshire, there are triangular manhole covers. They indicate the direction of flow in the sewer. Now these covers are being eliminated, as they do not meet modern safety standards.
The question is not always idle, even when it comes to hatches underfoot. Only by thinking about it, you can get new knowledge and use it in practice.
In each country, the development of sewerage systems took place in different ways, but the only common feature has always been the need to install sewer manholes.
The first manholes appeared together with the emergence of public utilities back in the 30s of the 19th century: then manhole covers had different shapes, but preference was most often given to round-shaped covers. Currently released, sewer manholes are round, and not of a different shape. This feature, in spite of everything, remained unchanged. But why exactly round?
Manhole covers are subdivided depending on their purpose. All of them have different patterns and embossing. On the old hatches you can see already outdated images of coats of arms, all kinds of drawings and inscriptions.
Modern manhole covers carry information about the manufacturer, serial number and date of manufacture. Some companies intentionally replace old sunroofs with new ("decorative") ones near their offices and usually put their logos on the covers.
Why was the round shape chosen for the hatches?
There are a lot of answers to the question why the hatches are round, but the following assumptions are the most reasonable:
- In our country, well tunnels and sections sewer pipes round, so it makes no sense to make covers of other shapes. At the same time, foreign experience knows many exceptions: for example, square manhole covers can be found in some cities of the Czech Republic and China, although they do not correspond to the shape of the wells they cover.
- Round sewer manholes will never fall into the well, which means they are best suited to perform their protective function. This is because the diameter of the covering circle is always larger diameter the well itself, and square covers can enter it, for example, at an angle.
- Hatches are made round in order to reduce the cost of their production. This is due to the specifics of the equipment: in order to make a round cap, less material is needed. Standard Norms hatch width - 600 mm, for a circle it will be a diameter, and for a square - a side, so the square hatch area will be 0.36 square meters, and round - 30% less.
- The manhole cover is round because it is convenient to carry. In most cases, sewer manhole covers are made from a grill (grey cast iron), which is obtained by melting various scrap metal. The weight of one cover varies from 50 to 110 kg. It is quite difficult for one person to transfer the manhole cover from one place to another, and thanks to its round shape it can be rolled.
- It is convenient to mount and dismantle hatches that are not square, namely round hatches, since load concentration points go along the entire circumference of the cover, while for square or rectangular hatches, only corners will have such points. That is why the necks and, accordingly, the lids for the jars are made round.
In fact, discussions about the shape of manholes may seem meaningless to many. However, few people know that such an unimportant question can take anyone by surprise when ... applying for a job! And this shouldn't be surprising.
This type of interview question is not uncommon. Eychars among themselves refer it to "cases", that is, keys with which you can give a more accurate assessment of some qualities and abilities of applicants.
This practice is used mainly during interviews for applicants applying for high positions. Thus, the fact of how a person behaves in case of force majeure, what his speed of thinking is, whether he knows how to use non-standard approaches, and so on is evaluated.
Many have faced the question of why sewer manholes have a round shape. Most have heard it in job interviews. In this way, "insidious" HR managers test the general erudition and ability for creative thinking of potential employees.
Also often this question is used in various competitions and quizzes. If you study the device of sewer manholes, then the answer to the question will become obvious and quite understandable. This is what we'll do.
Manhole device
A sewer well usually consists of a shaft and a working room, and the hatch serves as a cover. The working room is equipped and arranged depending on the type of serviced communications and the requirements for their operation. The depth of the shaft and the size of the room also depend on this.
- Usually 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. Usually the mine is round and 0.7 meters in diameter. There must be a ladder in the mine so that the worker can go down to the room. The material for the construction of the mine is usually brick or concrete.
- The cover on the sewer manhole is necessary to prevent foreign objects and people from entering the mine. The round shape prevents the cover from falling into the shaft if someone steps on it, which means it protects against accidents. This is the most main reason, according to which the shape of the sewer manholes is made round.
- Also, the covers have a fairly 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 the car wheels are moving, they fall on the cover. If the cover were light, it would easily turn 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.
- On the surface of the lid, there are usually raised stripes, letters, or other patterns and images. This is 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 sunroof. There are flat covers, and there are ones that are curved in the middle, but you will never find those that are concave inside.
On the wells of cable ducts, two covers are usually located at once - protective and locking.
The protective one is on top. A lock is additionally located on the locking cover, which prevents penetration into the shaft outsiders for the purpose of stealing the cable. These lids are lighter than conventional lids because they are made of steel.
Also, sewer hatches can be installed in gas, thermal, water and other wells. engineering networks, and storm sewers.
Each of them is designed to ensure that no unauthorized person or animal accidentally or specifically enters the sewer well, mine and does not get unhindered access to underground utilities.
Varieties 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 closes. Sewer hatches can close drainage systems, cable (electrical or telephone), storm drain systems.
Depending on the material used in the manufacture, cast iron, plastic, composite, concrete, reinforced concrete and rubber manholes, as well as manholes made of a polymer-sand mixture, can be distinguished.
Helpful information ! Each material has its pros and cons, taking into account which you can choose best option for a specific situation. But still, the traditional option is a gray or ductile iron manhole. This material has high strength, is resistant to mechanical stress of various nature, is independent of weather conditions, and its service life exceeds the shelf life of all other materials.
Manhole safety
The main purpose of giving the sewer manhole a round shape is to ensure the safety of the population. Unfortunately, cases of an adult or child falling into an open sewer shaft are not uncommon. If the mine is shallow, then this can result in one or more fractures, but a great depth can even threaten death.
Common causes such a fall is the theft of a manhole cover.
Now many people, walking down the street, are distracted by talking on a mobile phone or writing SMS messages, sometimes getting so carried away that they forget to look under their feet. This distraction leads to accidents.
Also, a car can get into an open hatch, which at best will lead to minor damage to the car, and at worst, to injury to passengers. Fans of riding other modes of transport are also in danger - scooters, motorcycles, mopeds, bicycles, roller skates or skateboards. Hitting the hatch at high speed is fraught with serious injury.
Fun Facts About Manholes
If the sewer hatch was installed a long time ago, then 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 have long been launched into production, into which a hook can be inserted and thus the cover pulled out.
But such hatches cannot be used when closing electrical, telephone and cable networks. This is due to the fact that water can get into the holes due to rain or snow melt, which can damage the networks and adversely affect the operation of the entire system.
The issue of the excess mass of sewer manholes should also be explained.
This weight is given to the lids specifically to make it difficult and sometimes prevent their theft. The fact is that free metal has always attracted fans to profit at the expense of the state. So, in the last decade of the twentieth century, several thousand manhole covers were stolen on the territory of the Soviet Union. Thieves rented them for scrap, thereby earning substantial money.
Helpful information! To avoid theft, currently used wooden shields, plastic hatches or concrete circles, which cover the main cover from above. Covers attached with the help of metal hinges. They cannot be simply removed and carried away; special equipment will have to be used, which will complicate the process of theft.
Also, the hatches are made so massive that teenagers do not play games in the sewers or use them for other, less decent things.
There are several other explanations for why sewer manholes are round.
- Firstly, this form facilitates transportation. The hatches are quite heavy and in order to move the cover, for example, a square one, you need to use the strength of one or even two adult men. The round lid can be easily rolled on the ground by any teenager and for any distance.
- Secondly, there are no problems when installing the cover. It is unlikely that anyone will have questions about its location in the hatch of the well. The only mistake here may be to install it on the wrong side up, but this is not very critical for operation.
- Well, and thirdly, less material is used for the production of round products.
Manhole covers are a familiar, familiar detail of the urban landscape, almost everywhere, in all countries of the world, having a round shape.
Why round - we will try to answer this question in detail.
Safety
The manhole cover of the sewer well is a massive product made of cast iron. It weighs more than 50 kilograms, and the weight of hatches located on the carriageway exceeds 78 kilograms.
This is not surprising, because the manhole cover located on the sidewalk of the street must withstand a load of 12 tons, and the cover lying on the road - 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 cover, then in the worst case, they will simply close the hatch. In this case, a rectangular or square cover can fall into a hole right on the heads of workers, because the diagonal of a square or rectangle is always more than any his side. Therefore, the round shape of the lid is the safest in this case.
Strength
Engineers have long known that round objects are much more durable than square ones. The sewer manhole is not only round, but also slightly convex towards the middle: this shape provides the greatest resistance to the 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 action of a load, the stresses are unevenly distributed, 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 cover, a corner may well break off from it. To split the round manhole cover, you will have to make a lot more effort. 
Judging by the fact that almost all lids have been lying intact for decades (and some for more than a hundred years), under normal conditions it is almost impossible to damage a round lid.
metal saving
Why is the round shape of hatches more optimal in terms of metal savings? With the same length of the perimeter of round and rectangular hatches - the area of the circle is always greater than the area of \u200b\u200bthe rectangle or any other geometric figure.
If we translate this into economic indicators, it turns out that a circle is the most advantageous form of a hatch, since it requires much less cast iron per cover (saving up to forty percent) than a rectangular cover.
The optimal ratio of the length of the perimeter to the area makes it possible to make round hatches not only for sewer wells, but also in much more serious structures - for example, between submarine compartments or spaceships. Round hatches are more economical and can withstand greater loads than hatches of any other shape.
Ease of work
The round manhole cover is much more convenient when carrying out repair or maintenance work. If a rectangular lid needs to be lifted to move it some distance, which will require at least two adult men, then a round lid can be safely rolled on its edge, and this task can be done 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 snap into place no matter which side you put it on. 
So, there are more than enough reasons why you need to make the sewer manhole cover round.
