Manholes are underground inspection chambers that provide access to underground utilities like a sewer system. These are one of the major sewer appurtenances and are classified into various types based on their depth and function.
There are three types of manholes they are normal, shallow, and deep. Every kind of manhole is chosen for different applications depending upon the function they need to serve and the size of the sewer or drainage water line. Manholes can be produced using a variety of materials comprising precast concrete, fiberglass, and plastic.
Types of Manholes Based on Depth
Based on the depth criteria, a manhole can be classified into:
- Normal Manhole
- Deep Manhole
- Shallow Manhole
1. Normal Manhole
- Normal manholes are generally 1.5 m in depth. They can take a square or rectangular dimension. Square [1m x 1m] and rectangular [1.2 m x 0.9 m].
- A heavy manhole cover is installed to bear the anticipated traffic load.Â
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Normal Manhole-Rectangular Cross-Section |
2. Shallow Manhole
- Shallow manholes have depths of less than 1 m around 0.7 m to 0.9 m.Â
- These manholes are constructed where the traffic loads are less usually at the start of the branch sewer. Hence, it forms the inspection chamber.Â
- Unlike a normal manhole, a shallow manhole is provided with a light manhole cover.
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Shallow Manhole |
3. Deep Manhole
- The depth of the deep manhole is more significant than 1.5 m.
- These manhole does not have a uniform cross-section throughout. It usually has a smaller upper portion. Steps are provided in such manholes for descending into the manholes.
- Deep manholes are provided with heavy covers to support heavy traffic loads.
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Deep Manhole |
Types of Manholes Based on Function
- Junction Manholes
- Drop-ManholeÂ
- Side-Entrance Manholes
- Scarper Type Manholes
- Flushing-ManholesÂ
1. Junction Manholes
2. Drop-Manhole
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Drop Manhole |
3. Side Entry Manholes
A side-entry manhole is a type of access point to an underground structure or network, such as a sewer or drainage system, that allows entry from the side rather than the top. The entry point to a side-entry manhole is a horizontal opening or doorway at the side of a vertical shaft or cylinder that extends from the surface to the underground structure.Side-entry manholes are often used in situations where there is limited space or access for equipment and workers, such as in urban areas or narrow streets, or where a top-entry manhole would be unsafe or impractical.
Side-entry manholes typically have a cover or lid that can be removed to allow access, and may also have features such as steps or ladders to facilitate entry and exit.
While designing, the floor of the side entrance passage should enter the chamber not lower than the soffit level of the sewer.
4. Scraper(Service) Type Manhole
Scarper or service-type manholes mandatory for all sewers with a diameter greater than 4.5 m. It is provided at an interval of 110 to 120 m.Scraper-type manholes have a clear opening that allows the lowering of buckets. The size of their openings ranges between 1.2 m x 0.9 m.
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