Sewer drains are round because this shape allows them to be installed in any direction without the risk of falling through the hole. It is the only shape that guarantees that a circular cover cannot pass through its opening.
A key point: the round shape simply prevents the lid from falling into the hole, no matter how it is positioned. Unlike a square or rectangular plate, a round lid can never slip through its own opening, which helps avoid quite a few accidents. Another safety advantage: round plates can be easily rolled on their edge, so there’s no need to strain your back lifting or carrying them. Additionally, their lack of corners allows for better weight distribution, making the surface stronger and more resistant to road traffic. Simple, effective, and clever.
A round shape naturally and evenly distributes weight and mechanical stresses. Unlike angular shapes, the circle avoids points of weakness where cracks or breaks could occur. This uniform distribution allows the cover to effectively support the weight of vehicles and frequent passage without deforming or quickly deteriorating. The round shape also keeps the cover stable: it cannot fall into the hole since it has no angles or diagonals shorter than the opening. A simple and practical solution to prevent accidents and unnecessary breakdowns.
A round lid is practical to move: to relocate it on the ground, you just need to roll it instead of carrying it. Less effort, less back pain. Thanks to their round shape, these lids can also be placed at any angle or orientation: this makes it much easier to set them up quickly when technical teams need to intervene in an emergency. Furthermore, the absence of sharp corners prevents premature wear of the edges, which reduces maintenance and avoids the risk of cracks or breaks. Finally, their symmetrical and regular shape also allows for simplified maintenance, as cleaning or inspecting a uniform circle is much easier than dealing with complicated nooks.
The rounded manhole covers date back to the time of the Romans, great pros of urban infrastructure, who were already building sophisticated underground networks to manage wastewater. Later, in the 19th century, during the industrial era in London and Paris, it was realized that a round shape allows for a stable, quick, and secure fitting of the covers. These large cities then naturally adopted this shape, which has since become an urban classic all over the planet.
Square or rectangular manhole covers present a big concern: they can fall into their own opening! Indeed, when positioned diagonally, they can easily slip through, creating a potential hazard for pedestrians and workers. Additionally, shapes with angles endure more mechanical stress at the corners, making them fragile against wear or impacts. Oval or polygonal covers unnecessarily complicate manufacturing, increasing costs and complexity. In short, these other shapes, although sometimes aesthetically pleasing, mainly bring problems of usability, safety, and durability.
Some modern manholes are equipped with electronic sensors to monitor groundwater flow in real-time and anticipate the risks of flooding or overflow in certain urban areas.
Historically, the choice of round manholes dates back to Roman times, when sewage systems already featured circular openings, which were practical for repairs and inspection.
In Japan, some cities decorate their manhole covers with true works of art, transforming these often-overlooked urban utilities into particularly original and appreciated tourist attractions.
In New York, cast iron manhole covers can weigh between 50 and 150 kilograms on average. This demonstrates how their round shape greatly facilitates their movement, as they can roll on their edge during handling.
A poorly closed manhole presents several significant risks, such as accidents where pedestrians or vehicles could fall into the opening. It could also lead to water infiltration in the event of flooding and cause health or environmental issues due to the improper disposal of wastewater.
In certain places, particularly in several cities in Japan and Europe, manhole covers are decorated to promote the city's image, highlight its historical and cultural heritage, or simply add an aesthetic touch to the urban space.
No, even though cast iron is often used for its strength and durability, there are also covers made from composite materials, concrete, or even reinforced plastic, depending on the specific requirements of each region or particular technical constraints.
Sewer grates should be regularly inspected, cleaned, and unclogged by specialized technicians to ensure the proper flow of wastewater and prevent sanitary issues. The round covers facilitate this operation due to their maneuverability and ease of opening.
Yes, some manhole covers can be square, rectangular, or triangular, especially in specific contexts. However, the round shape remains the most common due to its practicality and structural advantages related to safety.
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