Why sewer manholes are made round. Why sewer manholes are round: features, requirements and interesting facts

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. In this case, a rectangular or square cover 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 perimeter length of round and rectangular hatches, the area of ​​a circle is always greater than the area of ​​a 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 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.

All hatches manholes 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:

1. Work space;
2. Mine;
3. 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 through 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 a long service life. 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

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

1. Introduction

When our house was being 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 manhole covers are round. appeared before me problem: there are many geometric shapes, and for some reason sewer manholes are made round and perhaps there is some other figure suitable for manholes.

GOAL: defining wheel properties that are used in manhole covers.

TASKS:

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

2. Search for material on other geometric shapes that could be used by man in the manufacture of manhole covers.

3. Show the possibility of using circles (and if there is a figure similar in 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 parents, classmates and acquaintances my question and got different answers. Most people think that it is so convenient - it is easier to climb into a round hole, several answers were beautiful, and some answered that they did not know. Then I started looking for information on the Internet.

Experience 1. Round objects are easier to move - they can simply be rolled. While objects of rectangular and triangular shape interfere with the corners. And manhole covers are made even more heavy - they are made of cast iron. Then we can conclude that a round heavy cover can be moved by one person. A hatch of a different shape will have to be carried in several hands.

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

Experience 3. Draw two parallel tangent lines and fix the distance between them. Let's start spinning the circle. He constantly touches these lines and one can say that a closed curve (a circle that describes a circle) has a constant width. This is also a property of a circle. And it is taken into account in the manufacture of manhole covers - less likely to make mistakes in production.

Experience 4. Used in the manufacture of round lids less material and reduce their cost.

Here are the reasons why manhole covers are round. But I am interested in one more question: is there a figure similar in properties to a circle. And here the program that I watch - "Galileo" helped me. From it I learned that there is a figure similar in properties to a circle. This is the Reuleaux triangle. It was studied by the German scientist Franz Rehlo in the 19th century. Let's check this out too.

Experience 5. The 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 install a plank on 2 cylinders in the form of these triangles and see that it rolls.

Experience 7. Reuleaux's triangle, if placed on a manhole, will not fail either. I made such a layout and I suggest you check it out.

3. CONCLUSION

After doing the work, I was able to conclude that the hypothesis put forward by me - in addition to the circle, there are figures that can be used to make manhole covers, was confirmed. But to make round lids easier - less likely to make a mistake and, therefore, they are made. And now I can answer a question that is often asked when applying for a job at Microsoft. Here are the answers: safety, ease of movement, lower cost, fewer errors in their manufacture.

And I also learned a lot Interesting Facts .

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

2. In the early 2000s, a large art project “Sewerage of all countries, unite!” was held in Moscow. - where photographs of sewer manholes from around 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 program "Galileo" from May 2012.

Hello always dear friend!

There is a type of question that is considered to be a quick wits question. Sometimes this is true. But more often such questions are asked with several goals at once.Why hatches are round interview question just from this series. Although it is becoming less and less common, because it has already lost its former originality and the effect of surprise.

Let's remember that at the interview they want to evaluate not so much "Who are you?", but "What are you?".

1. How would you respond to this question? - the first goal of your interlocutor.

He wants to understand the degree of your emotional maturity.

2. Will you look for an answer to this question? is the second goal.

Let's remember that the employer is interested in several questions that he never asks directly. One of them: will you solve the problems that will inevitably arise in the course of your work.

Or you will look for reasons why the problem cannot be solved, or you will transfer problems to other people, including the leader.

3. The content of the response itself is the third goal.

Will you be able to solve problems that require intelligence and analytical thinking, logic?

If instead of answering you say “I don’t know” or “I find it difficult to answer”, this means that when faced with a difficult task, you are likely to save.

How to react?

Let's agree right away that we define this question “why the hatches are round” as, and not manipulative and not. Therefore, we respond constructively.

The worst thing you can do is puff out your cheeks and freeze something like this:

“Listen, what does this have to do with the subject of our meeting?”

After that, consider that you did not pass the test, although in fact you are right. The reason is that you did not accept the rules of the game that are offered to you. Again, this question is constructive and is not an attack on your personality. Therefore, it should be answered constructively.

Let's remember the principles of answering constructive interview questions:

1. If you are asked questions, that's good. If you are not asked anything, how will they know that you are the best applicant?
2. As a consequence of point number 1: Just give the interlocutor the right to ask any questions. Any question is your opportunity to be better than other candidates. You will answer confidently and calmly, and there is no reason to be afraid and nervous.
3. Majority are asked to get to know you better, not to hear the correct answer. That's what you came here for, so they know what a great candidate you are.

How to answer?

1. Listen to the end.
2. Verbal reaction - and with the tips of the lips (teeth closed!), A slight nod.
3. A small pause.
4. Answer.

The most simple and logical answer to this question is:

Round hatch - cannot fall into the well. No matter how hard you try and twist it. The square one has a diagonal longer than its sides, and when raised, it can slide down into the well. Drown or even injure someone. Besides -the diameter of the top of a round manhole is usually larger than the bottom, and it cannot slide in under any circumstances.

In addition, round hatches are more convenient to move - it can be rolled.

A couple more questions from the same series

About the cake

Himself Question: How to divide the cake into eight identical pieces using 3 cuts?

Answer: First, you should make a cross-to-cross cut, thereby dividing the cake into 4 equal parts. Next, make one cut horizontally in half along the entire diameter. The pieces turned out lower, but the problem is solved - you have 8 equal pieces.

The second option: after your two cuts, we have 4 pieces. We can put them on top of each other. Then divide all four pieces in half with one cut.

About light bulbs

There are three light bulbs in the room. There are three switches in the corridor leading to the room.

Question: How many times does the door need to be opened to determine which light corresponds to which switch?

Answer: It is enough to open the door once. We turn on 2 switches at the same time, then turn off one. We enter the room: we see that one lamp is on. It's from the first switch. Place your palm on each of the remaining two bulbs. Which is warm - the one from the second switch, respectively, cold from the third.

In the event that, if any intelligible answer does not come to mind, start thinking out loud. Trying to find the right one is much better than a nervous reaction or a “difficult to answer” response. Keep in mind that some of these questions do not have a clear answer at all.

Your attempts to find an answer, a train of thought, solutions are often more important than the answer itself.

Thank you for your interest in the article. I would appreciate a comment (at the bottom of the page).

Subscribe to blog updates (the form under the social media buttons) and receive articles on topics of your choice to your mail.

Have a nice day and good mood!

Logical tasks are given to job candidates to assess their analytical skills. Anyone can face such questions. But even if this does not 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 and get lost. As a rule, in most cases it is enough to show the course of your thoughts and ways to solve the problem. It may well be that the task does not have right decision or a clear answer. In no case should you say “I don’t know” or “I find it difficult to answer”, just think out loud.

So that you know what to be prepared for and not 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.

sewer manholes

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, the round hatch cannot fall into the 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: There are 3 light bulbs in the closed room and 3 switches in the hallway. What is the minimum door opening required to determine which switch belongs to which bulb?

Answer: For one opening. 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 bulbs remained on - this is the first switch, then we feel the remaining bulbs - warm and will be the second switch, and cold, respectively, the third.

Cake

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

Answer: First you need to make 2 cuts crosswise, dividing the cake into 4 equal parts. Then cut the cake horizontally in half. So what if the pieces have become low, but you have 8 equal parts. You can also, after the first two cuts, put the pieces on top of each other and halve them in one cut.

Dead man and match

Question: Found in the field dead man with a match in hand, no trace. What did he die of and under what circumstances?

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

Bus and balls

Question: How many tennis balls will fit on the bus?

Answer: The recruiter himself does not know the exact correct answer, since it does not specify what kind of balls and bus - their sizes are not known, and no one has checked this thoroughly. Therefore, the course of your thoughts is important here, you can only guess. Name the approximate length, width and height of the bus, 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 an empty bus. Decrease approximately this value, taking into account the seats and other details of the bus, make allowance for the fact that the balls are not square and give an answer. In this case, the process of finding an answer is more important than the answer itself. The options for the question can be different: footballs - footballs, instead of a bus - 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. Tablets should be drunk in two doses: in the morning, one tablet of each type and in the same evening. If you violate the dosage or do not take the pills, the patient will die. So it turned out that the pills were mixed. How to get treatment and survive?

Answer: Of course, we can say that it is better to go to the doctor and ask for more, it's still 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 these tasks and puzzles are primarily designed to test the candidate's behavior in non-standard situations, evaluate the ability to think, creative and logical approach. Alas, 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 better side and increase your chances of getting a job.