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Although It Seems Like an Urban Detail, the Circular Shape of Manhole Covers Has Technical, Practical, and Safety Reasons.
When walking down the streets, it is common to see manhole covers round. This shape has become part of the urban landscape, and we rarely stop to think about the reason behind this choice. But there are practical and technical reasons for it.
Advantages in Resistance and Manufacturing
Manhole covers are round mainly for reasons of resistance. As Larry Scheckel explained in his Q&A book about how things work, the circular shape allows the cover to better withstand the pressure of the surrounding ground.
Unlike other shapes, the circle distributes weight evenly, preventing deformation.
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In addition to resistance, the circular shape facilitates the manufacturing process.
Producing round covers is simpler than creating square or rectangular models. This makes the industrial process faster and more economical.
Ease of Handling in Daily Life
Another highlighted point is the weight of the covers. Since they are quite heavy, the round shape makes them easier to transport. They can be rolled from one point to another with less effort, something unfeasible with models that have corners.
During placement, the shape also offers advantages.
Workers do not need to align the cover precisely, as would be necessary with square covers. It is enough to position it over the hole, and it fits correctly.
Safety Against Falls
The main reason, however, is safety. Round covers do not fall into the hole.
All manhole chambers have a rim around the opening, with the diameter always smaller than that of the cover. Thus, even if the cover is placed carelessly, it is not at risk of falling.
In rectangular or oval shapes, there is a possibility that the cover could fall if positioned diagonally. The circle eliminates this concern, making the work safer.
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