What is the basic shape of a manhole?

• A. Rectangular
• B. Cylindrical
• C. Spherical
• D. Conical

Answer: (B)

Manholes are vertical access points to the sewer system. The chamber is designed to withstand the pressures from surrounding soil and any traffic loads above. A cylindrical shape distributes that external pressure evenly in all directions and avoids weak corners, which helps prevent cracks and leaks. It also matches the circular shape of the pipes it connects to, making joints easier to seal and the overall structure easier to manufacture and install using standard precast concrete sections. Rectangular shapes would create stress concentrations at corners and complicate sealing; a spherical form is strong but costly and impractical for a vertical access shaft; and while a conical top is common for transitions, the main underground portion remains cylindrical.