What factor determines the size and shape of a manhole?

The size and shape of a manhole is primarily determined by the number of ducts entering and leaving. This is because manholes are designed to provide access for maintenance and inspections of underground utility systems, such as sewer and drainage systems. Each duct requires a certain amount of space for safe and efficient operation, so as the number of ducts increases, the manhole must be larger in both size and shape to accommodate them.

While the type of materials used can affect the construction and durability of the manhole, it does not directly influence its dimensions. The burial depth can impact the structural design in terms of pressure and load-bearing capacity, but it is not a primary factor in determining the size or shape. Similarly, surrounding soil conditions may influence the construction method or need for reinforcement but are not a determining factor for the overall size and shape of the manhole itself.