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 hatches. First sewer hatches appeared in mid-19th century. Then they were made in a variety of shapes - from round to square. IN last years only models are made round shape. 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 underground system communications.

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;

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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.

Logic problems are given to job candidates to evaluate their analytical skills. Anyone can face similar questions. But even if this doesn’t happen to you, it will be simply interesting to study them for preparation.

Job seekers who encounter puzzles during the interview process should not panic or become confused. As a rule, in most cases it is enough to show your thoughts and ways to solve the problem. It may well be that the task does not have the right decision or a clear answer. Under no circumstances should you say “I don’t know” or “I don’t know,” just think out loud.

So that you know what to be prepared for and don’t get confused, we have collected the most popular puzzle questions and prepared answers and recommendations for them. Who knows, maybe you will come across exactly these tasks.

Sewage hatches

This is perhaps the most common question among all puzzles.

Question: Why are sewer manholes round?

Answer: There are several options. Since the diameter of the circle is the same, no matter how you twist it, then round hatch cannot fall into a well. A square, for example, has a diagonal larger than its sides, so the lid could fall off. You can also answer that round hatches are easier to transport and move.

Light bulbs

Question: B closed room there are 3 light bulbs and 3 switches in the corridor. For what minimum opening of the doors can you determine which switch belongs to which light bulb?

Answer: For one discovery. We turn on 2 switches at the same time, after a while we turn off the second one. We go into the room: one of the light bulbs remains on - this is the first switch, then we feel the remaining light bulbs - the warm one will be the second switch, and the cold one will be the third, respectively.

Cake

Question: How to divide a cake by 8 equal parts three cuts?

Answer: First you need to make 2 crosswise cuts, dividing the cake into 4 equal parts. And then cut the cake in half horizontally. So what if the pieces are not tall, but you have 8 equal parts. You can also, after the first two cuts, stack the pieces on top of each other and halve them with one cut.

Dead man and match

Question: Found among the field dead man with a match in his hands, no traces. Why did he die and under what circumstances?

Answer: A man died from a fall from a plane that began to lose altitude, and an accident was inevitable. There was not enough one parachute for all the passengers and they drew lots. He got a short match and was forced to jump without a parachute.

Bus and balls

Question: How many tennis balls can fit on a bus?

Answer: The recruiter himself does not know the exact correct answer, since it is not specified what kind of balls and bus they are - their sizes are not known, and no one has thoroughly checked this. Therefore, your train of thought is important here, you can only guess. Give the approximate length, width and height of the bus, and the dimensions of one ball. Calculate the volume of the bus and the ball - this way you will know how many balls will fit in empty bus. Reduce approximately this value taking into account the seats and other parts of the bus, make allowances for the fact that the balls are not square and give your answer. In this case, the process of finding an answer is more important than the answer itself. The question options may be different: the balls are soccer balls, instead of a bus there is a room, etc.

Pills

Question: The doctor gave the patient 4 tablets of two types - 2 tablets of each, which cannot be distinguished by appearance. The tablets should be taken in two doses: one tablet of each type in the morning and the same in the evening. If the dosage is violated or the pills are not taken, the patient will die. It so happened that the tablets were mixed. How to undergo treatment and survive?

Answer: Of course, we can say that it is better to go to the doctor and ask for more, after all, it is a matter of life and death. But these may be the only pills on Earth, the doctor may disappear under mysterious circumstances, etc. So you still have to answer. In addition, everything is quite simple: you need to divide each tablet into 2 parts and drink half of each tablet in the morning and evening.

Finally

Remember that primarily such tasks and puzzles are designed to test the candidate's behavior in unusual situations, assess the ability to think, creatively and logically. Unfortunately, there are often cases when the interviewer cannot correctly interpret the results of such questions, or does not understand their purpose at all. But even in this situation, confident behavior and the desire to come to an answer will show you with the best side and increase your chances of getting a position.

Quite often, when hiring a candidate for a position, they ask why sewer manholes are round. This is very unexpected question, which 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. Eat different theories and answer options. Let's try to figure them out.

Manhole cover

The lid is component hatch manhole, which must be present. In addition, it should be comfortable and ergonomic, and should not rattle when a car wheel hits it. It also contains 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 different 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 with minimal costs 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 often found, and in some countries they can represent a generally undefined geometric figure. Square shapes- 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 the metal required to make the lid for 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're talking about about an interview, it is not at all necessary to answer correctly. You can answer with a joke or even say that the hatches are from sewer wells not always round, it’s just the way it is 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.

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

The first hatches appeared along with the emergence of public utilities back in the 30s of the 19th century: then the manhole covers had different shapes, however, preference was most often given to round lids. 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 lids manholes can be found in some cities in the Czech Republic and China, although they do not correspond to the shape of the wells they cover.
2. Round-shaped sewer manholes will never fall into the well, which means they are best suited for fulfilling their purpose. 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 scraper ( 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 it is possible to 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.