Manhole covers come in various types, such as single-layer, double-layer, cast iron, ductile iron, composite, and cement concrete covers. Among these, ductile iron manhole covers are particularly popular due to their durability and strength. These covers are categorized based on load-bearing capacity, with different grades suited for specific environments:
- **Class 1 (A15)**: Suitable for low-traffic areas like green spaces and sidewalks, preventing access by lighter vehicles.
- **Class 2 (B125)**: Ideal for sidewalks, non-motorized zones, and trolley parks, accommodating moderate loads.
- **Class 3 (C250)**: Best for residential streets and areas with light vehicle traffic, ensuring stability within 0.5 meters of curbs.
- **Class 4 (D400)**: Designed for high-traffic urban roads, highways, and expressways, handling heavy loads effectively.
Manhole covers typically come in two primary shapes: round and square. In urban settings, circular designs are preferred for road administration due to their stability and safety. Circular manhole covers do not tilt easily and provide consistent protection for pedestrians and vehicles.
The advantage of using a circular ductile iron manhole cover lies in its geometry. Since the diameter remains constant across the circle, rolling the cover over won't allow it to fall into the well below, as the diameter is slightly larger than the well's opening. Conversely, square covers risk falling into the well along their diagonal lines, creating potential hazards.
This geometric principle also impacts material efficiency. Square covers often require more material to fit over a smaller well opening, whereas circular covers maximize usage while ensuring safety. In rural areas and cable wells, square covers are commonly used because they offer better liquid drainage and are easier to install in confined spaces.
Overall, the choice between circular and square manhole covers depends on the application and environmental factors. Circular covers dominate urban planning due to their safety and efficiency, while squares remain practical in rural contexts where functionality and cost-effectiveness are key considerations.
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