Why are manholes round? And what else can they be? Theoretically, the hatch can be square or rectangular in shape. But such a construction is rather an exception to the rule. The hatch is not a simple hole, it must be reliably closed. It should be easy to maintain and safe to operate.
If convenience is not for everybody, then the round cover design can provide reliability at the level of regulatory loads. The configuration of the base, which, in fact, is a sewer manhole, depends on its shape.
Sewage system
Sewer networks are a complex of structures designed to collect and dispose of wastewater from users to treatment facilities. The easiest way to do this is through underground utilities. A trench is dug out, pipes are laid in it along which drains will be discharged.
In order to be able to service the system over a certain distance, viewing shafts are necessary. In the conditions of urban infrastructure with dense buildings, the opportunity to conduct sewer networks is only along the roads or directly below them. In this case, with heavy traffic, the hatches must be securely closed. But why are the manholes round? They must have sufficient strength to withstand the maximum possible traffic loads.
In a big city, the number of inspection hatches and all kinds of mines can amount to hundreds of thousands. After all, this is not only a sewage system, it is also a communications network: water supply, heating systems, electricity, gas, telephony and more.
Manholes
For ease of access to communications, the well shaft is usually circular. Sewer rings used for the construction of such structures are most often made of reinforced concrete.
The cylindrical shape of the well is most suitable for maintenance. In such mines it is more convenient to carry out work. They are suitable for ventilation, since air circulation in a cylindrical object is more intense.
The size of the cover, the area of the base and the inner diameter are selected in accordance with the purpose of the viewing shaft. In this case, all elements of the system will correspond to each other as much as possible. The location, possible loads, traffic intensity are taken into account.
Why are manholes round?
It depends on the shape of the lid. On the one hand, service personnel should have convenient access to underground utilities. On the other hand, the well should be closed reliably to exclude the possibility of foreign objects getting inside, to ensure the safe movement of pedestrians and the passage of vehicles. A round lid is best suited for this, which means the hatch itself must be of this shape.
Depending on the purpose, they are divided by the type of communications laid under them: engineering cable networks, water supply, gas pipelines, heating mains, storm and sewage. The size of the sewer manhole in different countries is different. In Russia, standard dimensions (645 and 800 mm) are most often used. Hatches that are not manufactured according to GOST are designed and developed by manufacturers in accordance with the order and specific specifications.
Why is the manhole cover round?
This configuration has several advantages. Previously, hatches were made in various shapes. They could be square, rectangular, oval and even triangular to indicate the direction of water flow. However, the round shape of the lid was the most suitable.
It will never fall into the well, no matter how it rotates. The round lid is easier to open, so the point of application of force anywhere in the circle will be the same. It can be rolled by placing it on the rib. In the manufacture of such a design is more economical.
The round shape of the lid is less prone to subsidence. It can withstand a large load with the same thickness, which means that it can be made thinner without loss of quality. In the production of round castings give a lower percentage of marriage (shells, pores, cavities).
Material
The base and manhole covers for critical sewer wells are most often made of cast iron. This material is durable, which makes it possible to withstand heavy loads, and corrosion resistance for a long service life. The weight of the structures is sufficient so that passing vehicles cannot accidentally lift and slide the lid. Cast iron hatches are made by remelting secondary raw materials, they are cheaper than steel counterparts.
In places where there is no heavy car traffic, installing heavy and powerful structures is impractical. Recently hatches made of plastic, polymers and composite material have appeared. They are lighter, cheaper, have a sufficient margin of safety, a long service life.
In private homes, sewer rings made of reinforced concrete are used to equip sewage, equipment for inspection wells and septic tanks. In this case, it is justifiable to install on top of them the same base for the hatch. The cover is also made of concrete. It is made of a larger diameter, does not enter the groove, but simply closes the hole of the hatch. The massive structure is heavy enough, it is impossible to accidentally move it. This provides the necessary safety during operation.
Specification and Labeling
For increased loads on the roads use heavy hatches (class T). They can have a weight of more than 100 kg and a thickness of more than 100 mm. Where car traffic is not provided, use light hatches (class L). Structures for the garden, lawn and other territories (class A) have a diameter of 540 mm and a thickness of 50 mm.
Why are the manholes round and marked? This is done for the convenience of recognizing their belonging to public utilities. On their covers there are letters: - gas network, - main gas pipeline, - fire hydrant, etc.