A sewer manhole or inspection chamber is an underground structure designed to allow access to utilities such as sewer and drainage systems. These units enable the inspection, modification, cleaning, and maintenance of underground utilities.
The article briefly outlines the primary function, characteristics, and variations of a manhole.
Purpose of Sewer Manhole
The main purpose of a sewer manhole is:
- Inspection, cleaning, and obstruction removal in sewage line performed through manholes.
- Manholes utilized for joining sewers, changing direction, and aligning sewer lines.
- Perforated covers on manholes allow escape of foul gases, aiding ventilation.
- Manholes assist in laying sewer lines in conventional lengths, enhancing system efficiency.
Features of a Sewer Manhole
The key components of a manhole include the chamber or ring and the Vertical Circular Pipe, which comes in various depths and sizes to facilitate access to inspection joints within the system.
Manholes are typically situated around 0.5m away from the road’s curb lines and are strategically positioned to avoid interference with traffic flow.
The cover of a manhole serves as a protective plug, preventing unauthorized access. These covers can be rectangular, square, or circular in shape, and they are constructed from materials such as precast concrete, composite materials, or glass-reinforced plastic.
Access to the manhole is facilitated through steps, with a step ladder utilized for manholes less than 1m in depth, and a regular ladder installed for depths exceeding 2.5m. However, modern manholes often allow access without physical entry.
Types of Sewer Manholes
The categorization of manholes into three primary types is based on their depth:
- Shallow sewer Manhole
- Normal sewer Manhole
- Deep sewer Manhole
1. Shallow Sewer Manhole
A shallow manhole is not very deep, usually between 75 to 90 centimeters. They’re put at the beginning of a smaller sewer line or in places where there isn’t a lot of traffic. Instead of a heavy cover, they have a lighter one called an inspection chamber.
2. Normal Sewer Manhole
These things are at the sewer line with a heavy lid on top. They are 150cm deep. Regular manholes are square.
3. Deep Sewer Manhole
A deep manhole is made deeper than 150cm with a really heavy cover on top. It can be made bigger, and it’s easier to get down into it.
Materials Used for Sewer Manhole Construction
There are three main kinds of manholes depending on what they’re made of:
- Plastic Manholes
- Precast Concrete Manholes
- Fiberglass Manholes
1. Plastic Manholes
Plastic manhole covers are made from a strong material called polyethylene. They’re built in one solid piece, without any seams or seals. This helps prevent maintenance problems.
Plastic manholes are good for the environment and can last a long time without getting damaged. They don’t harm the soil or the ground they’re on. Also, they don’t rust or wear out easily, so they don’t need to be fixed or looked after often. Plus, they come with handy extras like ladders and covers.
2. Precast Concrete Manholes
Building manholes with precast concrete is an old-fashioned way. The frames for these manholes are made in a factory away from the construction site.
This helps make sure they’re good quality and makes it easier to put them in quickly. Then, the pre-made manholes are put together at the site where they’re needed.
3. Fiberglass Manholes
Fiberglass manholes are made with two parts: a barrel and a cover. They also have extra parts like grinder channels, weirs, and separators for stormwater. All these parts are joined together using fiberglass technology, so they act as one solid piece with no gaps.
