Manhole covers are round primarily because a round shape cannot fall through its circular opening, while other shapes like squares can if inserted diagonally. Additionally, round covers are easier to manufacture, more material-efficient, and simpler to roll and move. The round shape also distributes the earth's pressure evenly and matches the round manhole openings that are typically made by rotational tools. The circular design allows for easier installation without needing to line up edges and provides strength and safety against traffic loads.
Reasons for Round Manhole Covers
- Safety: A round cover can't fall into its hole, unlike square or rectangular covers which might fall through if turned diagonally.
- Manufacturing: Circular covers are easier and cheaper to make due to less surface area and simpler casting and machining.
- Functionality: Round covers fit round manholes that are created with rotational tools and evenly distribute pressure.
- Mobility: Round covers can be rolled for easier transport.
- Installation: No alignment is needed for circular covers to fit properly.
- Strength: A circle is structurally the strongest shape under compression, distributing forces evenly around the edges.
These practical and engineering benefits combine to make round manhole covers the preferred choice worldwide.
