Types, Purpose, & Components of Manhole
A manhole is an opening, to a sewer line or in any utility service. Manholes are usually used as an access point for an underground utility like sewer systems, water, electricity, telephone and etc. A manhole is used for inspection, maintenance, and cleaning purpose. Manholes can be found in streets and sidewalks particularly in urban areas.
Purpose of Manhole
- The main purpose of a manhole is:
- The main purpose of constructing a manhole is to give access to the underground systems for cleaning, repairing, removing the obstruction, and inspection works.
- With the help of a manhole, sewers line direction and alignment can be changed and also joining the sewers.
- For ventilation of underground sewer line, fixed a perforated cover in the top of the manhole which also discharges foul gases.
- Manholes help to manage the suitable length of the sewer line.
Types of Manhole
Manholes can be classified into three types depending on their depth,
- Shallow manhole
- Normal Manhole
- Deep Manhole
The depth of shallow manhole is given from 75cm(2′) to 90cm(3′). It is constructed at the start of the branch sewer or at a place that is not used for heavy traffic. There is fixed a light cover on its top. It is also called an inspection chamber.
The depth of a normal manhole is not less than 90cm and it can construct up to 150 cm in a sewer line. These types of manholes are usually provided with a heavy cover on the top. It is constructed normally square or rectangular shape.
The depth of the deep manhole is more than 150 cm. These manholes are generally in circular shape where the diameter can vary on the depth of the manhole. The size is gradually increased from top to bottom and a facility for going down is provided. These types of manholes are usually provided with a very heavy cover on the top.
Location of Manhole
Manholes are normally provided at the following locations:
- If there is a change in the size of the sewer line.
- If there is a change in the alignment of the sewer line.
- If there is a change in the grade of the sewer line.
- At the junction of two or more sewers lines.
- Manhole is also constructed in the straight alignment of sewers at regular intervals depending upon the diameters of sewers.
Features and components of Manhole
A manhole is constructed 50cm away from the curb line such that it is enough far from the wheel line of the traffic.
A manhole mainly contains an underground chamber of different sizes and depths. Manholes have several components.
The main part of a manhole is the chamber and the Vertical Circular shaft. The access shaft leads to the working chamber. These shafts are used to access the inspection joints in the system.
The lower part is the manhole is the working chamber. It provides the actual working area for executing inspection, repair, and maintenance activities. The working chamber of a manhole is normally larger than the access shaft to provide sufficient space for working.
The bed of a manhole is usually constructed of plain cement concrete. This avoids the access of underground water inside the chamber as well as gives support to the side walls.
The bed of concrete may also be reinforced to give extra strength. The side walls are usually constructed of brick masonry or reinforced cement concrete.
A number of steps are provided for the entry and exit for the workers.
Steps are mostly composed of cast iron. If the depth of the manhole is less than 1 m, a step ladder is constructed. If the depth of the manhole is greater than 3m, a regular ladder is fitted.
The top opening of a manhole is given with a cover in a frame. The frame provides support to the cover of the manhole. The covers used for manholes can be rectangular, square, or circular in shape. The material of cover can be precast concrete or any composite material.
Types Based Upon Material
Types based on the different materials used for the construction of manholes:
Polyethylene material is used for the manufacturing of polyethylene manholes. A polyethylene manhole has resistant against sewer contaminants such as acids and alkies. Polyethylene materials are durable against abrasion, erosion, and contact with drowning particles in the sewers and have extensive stability.
The raw material for polyethylene is ductile, so it does not suffer from detachment and erosion puts in by the drowning particles in the sewers. The polyethylene manholes are completely sealed due to one-piece manufacturing, therefore no underground water will go into the sewer system and these manholes also do not enable the sewer materials to penetrate into underground water storage tanks and therefore make the sewer system truly helpful.
These manholes also avoid underground water storage tanks from contamination which is completely inconsistent and conformity with the environment.
Precast Concrete Manhole
The precast concrete manholes are manufactured in various sizes in the factory and delivered on-site carefully. The manufactured precast manholes are assembled on the site.
This is a traditional type of manhole. With this procedure can get good quality and also quick installation.
Precast manholes are widely used worldwide because of their extensive life span.
These types of manholes are produced by fiberglass technology. They contain manhole barrels, cover, weirs, flumes, separation units for stormwater, etc. The handling and installation of fiberglass manholes are easy due to their lightweight. Fiberglass manholes are environmentally friendly are highly durable.