home · Installation · What you need to know about the shape of sewer manholes. Why are the hatches round? Unexpected interview question: Why is the sewer manhole cover round?

What you need to know about the shape of sewer manholes. Why are the hatches round? Unexpected interview question: Why is the sewer manhole cover round?

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

The first manholes appeared along 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 covers round shape. Currently produced, sewer manholes are round, and not of any other shape. This feature, despite everything, has remained unchanged. But why exactly round?

Manhole covers are divided depending on their purpose. They all have different patterns and embossing. On old hatches you can see outdated images of coats of arms, all kinds of drawings and inscriptions.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 deliberately replace old hatches with new (“decorative”) ones near their offices and, as a rule, put images of their logos on the covers.

Why did you choose a round shape for the hatches?

There are quite a lot of answers to the question of why hatches are round, but the most reasonable assumptions are the following:

  1. In our country, well tunnels and sections sewer pipes round, so there is no point in making lids 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 fulfill 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 fit into 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 produce a round lid, it is necessary less material. The standard norm for the width of a hatch is 600 mm, for a circle this will be the diameter, and for a square this will be the side, so the area square hatch will be equal to 0.36 square meters, and round - 30% less.
  4. The manhole cover is round because it is easy to carry. In most cases, manhole covers are made from scrap (gray cast iron), which is obtained by melting various scrap metals. The weight of one cover varies from 50 to 110 kg. It is quite difficult for one person to move the manhole cover from one place to another, but thanks to its round shape it can be rolled.
  5. Not square, but round hatches are convenient to install and dismantle, since load concentration points run along the entire circumference of the cover, while square or rectangular shape only the corners will be such points. That is why the necks and, accordingly, the lids of the jars are made round.

In fact, discussions about the shape of sewer manholes may seem pointless to many. However, few people know that such a question of no particular importance can take anyone by surprise when... applying for a job! And you shouldn't be surprised by this.

This kind of interview question is not uncommon. HR managers among themselves refer it to “cases,” that is, keys with the help of which they can give a more accurate assessment of certain qualities and abilities of applicants.

This practice is used mainly during interviews for applicants applying for high positions. In this way, the fact is assessed how a person behaves in the event of force majeure, what speed of thinking he has, whether he knows how to use non-standard approaches And so on.

The eternal question: “Why is the hatch round?”

Almost all manholes in the city are covered with special round covers. If you carefully study such objects, it turns out that they are the same all over the world. This involuntarily prompts the question: “Why are the covers on sewer manholes round? Why do the technical objects themselves have exactly this shape, and, for example, not square?” It turns out that the answers lie on the surface.

Some details about sewer manholes

The described items are made of cast iron or concrete. They are specially made heavy and unbearable, so that no one would have the desire to take a “useful” thing with them. Opening a technical hole on your own is not so easy, and this is specially provided for in the design for the safety of passers-by.

Sewage hatches have conditional classification. They are divided according to the material of manufacture and the type of communications passing under the launch shafts. Therefore, experts highlight:

  1. Drainage systems.
  2. Storm drains.
  3. Electrical networks.

Hatches are made from high-strength cast iron and plastic, a special polymer-sand mixture, composite materials and reinforced concrete. But they are all invariably round in shape. Why, let's find out.

Logical explanation

So why is a manhole round? Described technical object consists of several parts - a round shaft, an inspection room and a lid.

The viewing room can have different shapes. It all depends on what communications are laid in the well. Dimensions are chosen taking into account the ease of their maintenance. But the mines are invariably made round. The diameter of the oval is 0.7 meters. They are assembled from brick and additionally equipped with a ladder that helps the service worker to go down without hindrance.

The top of such a hatch must be closed with a lid. It prevents various types of foreign objects from entering sewer systems that could cause accidents. Almost everywhere the lid has a round shape. Why not square? Because in any position, such a lid will never fall inside and hit the person located there.

A square lid can easily fall inside under the influence of vehicles, slipping through at an angle. After all, the diagonal of a square is always greater than any of its sides. A circle has the same radius, no matter how you look at it.

Typically, manufacturers produce lids that weigh more than 50 kg. This is done so that no heavy traffic of cars could move them.

Other explanations for the shape of the hatches

It is very rare to find such a form

There are several more explanations to help understand why manhole covers are round:

  • Firstly, a circle has a higher ratio of cross-sectional area to circumference than a square or rectangle. This allows the lid production process to reduce material costs and save on product production.
  • Secondly, the round shape reduces internal forces, which invariably arise when installing any cover on an object. And this also provides savings on the production of the product, since in this case it is possible to produce lids of smaller thickness.
  • Thirdly, the round shape helps reduce the production of defective products. By reducing the number of reference lengths, the likelihood of errors leading to the appearance of uneven protrusions and other characteristic defects is reduced.

And further. The round lid is much easier to transport for one person. He can just roll her to the place. A square or rectangular one will have to be carried in several hands.

The above arguments show that the choice of form is explained by elementary practicality.

Fun facts

There are known cases around the world of using lids of other shapes. For example, in the American city of Nashua you can still see sewer wells covered with triangular covers. Their sharp corners indicate the direction of flow Wastewater, and until recently this helped repair teams to navigate well. But today their use is considered unsafe, so the prefecture is dismantling them and replacing the triangles with circles.

Other forms are also found

Now you know why sewer manholes are made round. And that’s why they are made so massive and heavy - also interest Ask. Although the explanation lies on the surface. The weight ensures relative safety from theft and delivery of the described products to metal collection points. About 10 years ago, a wave of characteristic crimes swept across the country. Lids began to disappear en masse, so the designers came up with an interesting solution.

Most modern sewer wells They don’t just cover it with a massive object that one person can’t carry away. The lids were placed on strong hinges, and they turned into real doors, which were additionally locked.

There is no way to leave the well open, especially those in which storm drain and plumbing. Their depth sometimes reaches 6 meters, and at the bottom technical room a lot of protruding pipes and pieces of fittings. If a person falls there in the dark, it will end in death. Therefore, those who are responsible for sewer hatches - and this is the district administration - have a great responsibility for safe use of this technical structure.

Who else could be responsible for the hatches?

But the Russian people are still accustomed to seeing such a hatch

There are wells that are not municipally owned, but belong to the property apartment building or to the property of a specific legal entity.

All ownerless objects are first registered by the body that registers the right to property. This happens according to the statement of the authority local government. Then, through the court, everyone can challenge their own right. If there are no volunteers within a year, all ownerless objects are transferred to the departments of specialized companies.

Generalization on the topic

The round shape of sewer manholes is more practical than all other types. Over many years of operation of sewerage structures, it has been proven that round holes are more technologically advanced and have a longer service life. And all because such a hatch is more resistant to temperature changes.

The development of sewer systems in each state took place in its own way. The only one common feature in all cities it is necessary to install hatches. Sewage hatches first appeared in the middle of the 19th century. Then you made them yourself different shapes– from round to square. IN last years Only round models are made. Why?

What is a manhole?

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

Types of sewer manholes

Lids are divided into types. There are different embossing and patterns on them. For example, on the first sewer manholes they depicted the state emblem and propaganda slogans. Now the covers display the serial number, date and initials of the manufacturer. Sewer people highlight:

  • Plastic;
  • Iron;
  • Rubber;
  • Cast iron;

Related materials:

Why do spiders weave webs?

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

Why are sewer manholes round?

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

  1. The cost of manufacturing a housing for a round hatch is lower than any other shape (triangular, diamond-shaped, rectangular);
  2. Ease of movement. A round hatch is much easier to move: you just need to place it on its edge and roll it in the desired direction;
  3. The round hatch is easier to open. For him, any point on the circle is a stress concentration. For example, all lids for jars are also only round;
  4. The round hatch will not fall through sewer system. Any other form has a high probability of subsidence below the established level;
  5. The cross-section of the system pipes is round. It would be logical to make the same shape as the lid that covers the sewer system.
  6. It is impossible to remove a square (triangular, rectangular) object through a round hatch cover.

Triangular sewer manhole

In fact, at first they were different: in many countries other shapes were used, but the “winner” was still round. They are used all over the world to this day.

What is the difference between manhole covers? Everything except the form. On top of them, at the dawn of their mass use, there could be images of various coats of arms, motives of events, and memorable dates. Today everything is much simpler: a simple pattern and information about the manufacturer of the lids and the customer for their production. Large companies sometimes place “decorative” ones near their offices.

So why are hatches round?

  1. Because well tunnels and sewer pipe cross-sections are also round. Therefore, there is simply no point in using another shape; round is the most convenient.
  2. Because round lids hatches never fall into the well. But square ones, for example, can do it without problems.
  3. Because it's cheaper. To cover a round “hole” with a diameter of 60 centimeters square lid, the area of ​​such a cover should be 0.36 square meters. At the same time, perform this task you can use a round hatch with an area of ​​0.28 sq. m. Noticeable difference?

Because it’s more convenient to carry them this way. Or roll, because the weight is not small - from 50 to 110 kg: one person may not be able to handle it. What if they were also square?

Because round hatches more convenient for installation and dismantling. They have load concentration points along the entire perimeter, and in square ones - only in the corners.


However…

“Who cares why sewer manholes are round,” you ask? I would like to answer that no one is interested in this, but there are precedents. And they happened at very serious events, in the offices of reputable companies. The fact is that sometimes HR managers like to ask unexpected questions during interviews to see how a person behaves in force majeure situations. Just ask someone out of the blue, why are hatches round? Do you think you will immediately hear a clear answer? No! So they torment applicants for high positions in the private sector with insidious and at the same time stupid questions.

The text of the work is posted without images and formulas.
Full version work is available in the "Work Files" tab in PDF format

1. Introduction

When our house was built, they laid water and made a well, which was then covered with a special manhole cover. I noticed that in our city there are round lids everywhere: in our yard, on the roads, and near the school.

And then I became interested in why the lids sewer hatch round. appeared before me problem: there are many geometric shapes, and for some reason sewer hatches are made round and perhaps there is some other shape suitable for hatches.

TARGET: determination of the properties of the circle that are used in sewer manhole covers.

TASKS:

1. Get acquainted with the properties of the circle that are new to me and, with the help of experiments, establish the simplest connections and draw conclusions.

2. Look for material about others geometric shapes, which could be used by humans in the manufacture of manhole covers.

3. Show the possibility of using circles (and if there is a figure with similar properties) in life.

Hypothesis: In addition to the circle, there are shapes that can be used to make manhole covers.

Research methods

1. Conducting a survey “Why are manhole covers round?”

2. Search for materials on the Internet.

3. Observations.

4. Conducting experiments.

2. MAIN PART

I asked my question to my parents, classmates and acquaintances and received different answers. Most people think that it’s convenient - it’s easier to crawl into a round hole, several answers were - it’s beautiful, and some answered that they don’t know. Then I started looking for information on the Internet.

Experience 1. Round objects are easier to move - you can simply roll them over. While objects have rectangular and triangular shape The corners are in the way. And manhole covers are made even heavier - they are made of cast iron. Then we can conclude that the round heavy lid can be moved by one person. A hatch of a different shape will have to be carried in several hands.

Experience 2. A round manhole cover will never fall into the well, which means it is best suited for protective function. All this is because the diameter of the lid is always larger than the diameter of the well itself. And other figures may fail (for example, at an angle).

Experience 3. Let's draw two parallel tangent lines and fix the distance between them. Let's start rotating the circle. It constantly touches these lines and we can say that the closed curve (the circle that describes the circle) has a constant width. This is also a property of a circle. And it is taken into account when making manhole covers - there is less chance of making mistakes during production.

Experience 4. When making round lids, less material is used and their cost is reduced.

It turns out that there are reasons why manhole covers are round. But I’m interested in one more question: is there a figure with properties similar to a circle? And here the program I watch, “Galileo,” helped me. From it I learned that there is a figure with properties similar to a circle. This is the Reuleaux triangle. It was studied by the German scientist Franz Reuleau in the 19th century. Let's check this out too.

Experience 5. A Reuleaux triangle is a figure that has a constant width. We draw two tangent straight lines, fix their width and begin to rotate the Reuleaux triangle. And always one point located in one of the “corners” of the Reuleaux triangle, and the other on the opposite arc of the circle, will touch the lines. Experience 6. An object made in the shape of a Reuleaux triangle can roll. Let's place a board on 2 cylinders in the shape of these triangles and see that it rolls.

Experience 7. The Reuleaux triangle, if installed on the hatch, will also not fail. I made such a model and I invite you to check it out.

3.CONCLUSION

After carrying out the work, I was able to conclude that the hypothesis I put forward - in addition to the circle, there are figures that can be used to make manhole covers - was confirmed. But it’s easier to make round lids - there’s less chance of making a mistake, and that’s why they make them. And now I can answer a question that is often asked when applying for a job at Microsoft. These answers are: safety, ease of movement, lower cost, fewer errors in their manufacture.

And I also learned very much Interesting Facts.

1. When car races are held on city streets, the covers are welded to the hatches. When racing cars move, their aerodynamic characteristics create such low air pressure between the road and the bottom of the car that it is enough to lift a manhole cover.

2. In the early 2000s, a large art project “Sewers of all countries, unite!” took place in Moscow. - where photographs of sewer manholes from all over the world were presented.

4. LIST OF LITERATURE AND RESOURCES

1.http://www.etudes.ru/ru/etudes/mazda

2.http://otvetprost.com/387-pochemu-lyuki-kruglye.html

3.http://expirience.ru/pochemu-lyuki-kruglye/

4.Recording of the Galileo program from May 2012.