Why is the well round and not square? What you need to know about the shape of sewer manholes. Manhole covers: weight and maximum load

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.

Security

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. A rectangular or square lid in this case can fall into the pit right on the heads of the workers, because the diagonal of a square or rectangle is always greater than any of its sides. 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, stresses are unevenly distributed under the action of a load, 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 ​​the rectangle or any other geometric figure.

If we translate this into economic indicators, then it turns out that a circle is the most advantageous form of a hatch, since it requires much less cast iron per lid (saving up to forty percent) than a rectangular lid.

The optimal ratio of the length of the perimeter to the area makes it necessary to make hatches round 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 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.

Why are hatches round? Those that close-open the entrance to the sewer system. Those that have to be bypassed so that misfortune does not happen. They so habitually entered everyday life that many people do not notice a foreign object in their path and automatically step over a dangerous place.

There are also car owners who diligently go around the sewer outlets to the surface in order to save the suspension. For this reason, the question of the shape of the lid can be quite worrying. a large number of of people.

Why was this form chosen?

Man is a being of a higher order, thanks to his ability and desire to discover the world, to seek and find answers to questions of interest. And people are very curious. Why are giant elephants afraid of mice? Where do the fallen stars go? How to make a magic wand? Why is the manhole cover without corners and extra loops?

Of course, there are squares, stars, triangles on the pavement. But this happens so rarely that it can be classified as an exception. And the pattern is a hatch in the shape of a circle. And there are several reasons for this:

1. The ideal shape for sewer wells is round. They are easier to maintain. The likelihood of clogging is minimal. It is clear that for closing wells it is most rational to use covers of the same shape, but in a slightly increased diameter.

2. The production of round caps is cheaper for factories than the production of other forms. This is mainly due to material savings. What is a circle? This is a pretty good geometric figure. With a limited amount of material, choosing just such a shape will allow you to get the maximum area (compared to other figures). After all, the ratio of the cross-sectional area of ​​\u200b\u200bthe circle to the circumference is greater than that of squares or rectangles.

3. You can also save on thickness if you choose the right hatch shape. The resulting load is evenly distributed, reducing the internal pressure, only in a circle. Therefore, the lid can be thinner, even while maintaining its strength and reliability.

4. The sewer hatch covering the circular well will not fall inside. From no position. And this additional measures safety for plumbing work.

5. Each point on the circumference of the hatch is a point of stress concentration. The uniform distribution of the load, which has already been mentioned above, has another advantage. It is this form that makes it easier to open the well by shifting the heavy cover to the side.

With rectangular hatches, it's a little different. There tension is concentrated in the corners. With such covers you have to tinker.

6. Round options are easier to move, not only because of the distribution of the load, but also simply because of the absence of corners. As a rule, sewer covers are made of cast iron. This is very heavy material. And any product from it is almost unbearable. The circle can be put on edge and rolled.

In addition to the above reasons, one more important point should be mentioned. There is such a production pattern: the less protrusions and corners a part has, the less marriage will come out from under the machine. Therefore, the production of round hatches is more than justified.

The development of sewer systems in each state took place in its own way. The only common feature in all cities is the need to install manholes. Sewer manholes first appeared in the middle of the 19th century. Then they were made in a variety of shapes - from round to square. IN last years only make models round shape. Why?

What is a sewer hatch?

A manhole is a hole in concrete or ground that provides access to underground utilities. This hole is always closed with a lid, hatch, to avoid accidents. The hatch has another function - to prevent illegal entry into the underground communications system.

Types of manholes

Covers are divided into types. On them there are different embossing, patterns. So, for example, on the first sewer manholes depicted the coat of arms of the state, propaganda slogans. Now the covers display the serial number, date and initials of the manufacturer. Sewer people emit:

• plastic;
• iron;
• rubber;
• cast iron;

India is considered the leader in the manufacture of sewer manholes.

Why are manholes round?

For many years in a row, exclusively round hatches have been produced. There are several reasons for this:

1. The cost of manufacturing a case for a round hatch is lower than any other shape (triangular, diamond-shaped, rectangular);
2. Ease of travel. The round hatch is much easier to move: you just need to put it on its edge and roll it in the right direction;
3. The round hatch is easier to open. He has any point of the circle is the concentration of stress. For example, all lids for jars are also only round;
4. The round manhole will not fall into the sewer system. Any other form has a high probability of subsidence below the established level;
5. The cross section of the pipes of the system is round. It is logical to make the same shape and cover that closes the sewer systems.
6. An object of a square (triangular, rectangular) shape cannot be taken out through a round manhole cover.

In some countries, triangular sewer manholes are used. In Nashua (a city in the USA), underground systems are still covered with triangular lids. The sharp corners of the triangle indicate to the repair team the direction of the sewage flow. However, such hatches were recognized as hazardous to health, and their dismantling began.

The choice of a round shape of sewer covers is dictated by elementary practicality. Such hatches last longer, they are resistant to influence environment. Less material is used to manufacture, they are cheaper. Convenient to work if you need to get inside sewer system are safe. The probability of subsidence of the round hatch is very small.

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 entry into the mine foreign objects and people. 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 main reason why the shape of 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 unauthorized persons from entering the shaft in order to steal 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 stranger or animal accidentally or specifically entered into sewer well, a mine and did not receive 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 manholes can close drain 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.

Useful information ! Each material has its pros and cons, taking into account which you can choose the best option for a particular situation. But still, the traditional option is a gray or ductile iron manhole. This material has high strength, resistant to mechanical stress. different nature, 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.

A common cause of such falls 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.

Useful information! To avoid theft, currently used wooden shields, plastic hatches or concrete circles, which cover the main cover from above. Covers fastened with metal hinges have also become widespread. 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.

In each country, the development of sewerage systems took place in different ways, but the only common feature there has always been a need to install sewer manholes.

The first manholes appeared along with the emergence of utilities back in the 30s of the XIX century: then manhole covers had different shape, however, preference was most often given to round lids. 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:

1. 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.
2. Round sewer manholes will never fall into the well, which means they are best suited to perform their protective function. And all because the diameter of the covering circle is always greater than the diameter of the well itself, and square covers can enter it, for example, at an angle.
3. 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. The standard hatch width norms are 600 mm, for a circle it will be a diameter, and for a square it will be a side, so the square hatch area will be 0.36 square meters, and round - 30% less.
4. 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.
5. 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. In this way, the fact of how a person behaves in case of force majeure, what speed of thinking he has, whether he knows how to use non-standard approaches, and so on, is evaluated.