Manholes or Inspection chambers are underground structures that are built for inspection of utilities like a sewer system, drainage system, etc. This underground inspection chamber helps for cleaning, maintenance, and repair works.
Purpose of Manholes
Manholes serve various purposes as mentioned below:
- The main purpose of a manhole is to perform inspection, cleaning, maintenance, and repair in the sewage line.
- To eliminate the foul gases with help of a perforated cover, which acts as ventilation for the underground sewage system.
- Inspection chamber are useful in laying the sewer line in conventional lengths.
- Manhole helps in joining sewer, alignment of sewers, and changing the sewer direction.
Also Read – What is Sewerage? Different Types of Sewage system
Types of Manholes
Based on their depth, They are classified into three different types of manholes.
- Shallow Manhole
- Normal Manhole
- Deep Manhole
Shallow manholes are generally constructed at the start of a branch sewer. These are usually 75 to 90cm deep and a light cast iron cover is provided at the top of the sewer for inspection purposes, which is known as the inspection chamber.
Normal Manhole or Medium manhole which has a depth of 150cm. Constructed at a sewer line with heavy cover at the top. These manholes are square or rectangular in shape.
Deep manholes are provided at a depth of more than 150cm and a heavy cover is provided at the top. The size of the manhole can be increased and the facility for going down is also increased.
Usually, manholes are provided at certain locations where :
- Change of sewer line is necessary
- At the junction where multiple sewer lines are formed.
- Where Sewer size and alignment change are necessary.
Also Read – Characteristics of Wastewater- Physical | Chemical | Biological
Manhole Construction Materials
There are mainly 3 types of manhole or Inspection chambers based on the type of material used in construction:
- Plastic Manholes
- Precast Concrete Manholes
- Fiberglass Manholes
Plastic Manholes or Inspection Chamber
Plastic manholes are eco-friendly and more sustainable, usually manufactured using polyethylene material. Plastic manholes do not contaminate the ground where it is placed.
These manholes are manufactured with additional features like ladders and a cover at the top. These are resistant to corrosion and do not require any frequent maintenance and repair works.
Precast Concrete Manholes or Inspection Chamber
Precast concrete manholes are engineered pre-built materials that are manufactured in a factory. This type of manhole is manufactured using concrete which is a traditional method.
These Precast concrete manholes have a lifespan of 100 years which makes the main reason for its consideration.
Fiberglass Manholes or Inspection Chamber
Fiberglass manholes are manufactured in such a way that it includes a manhole barrel and a cover and also includes some additional features like weirs, flumes, grinder channels, and separation units, etc.
A fiberglass manhole is a complete combination of several units or parts, This type of manhole is engineered to seal the units together, which behaves like monolithic without any requirement of seams or seals.
There are many factors to consider Fiberglass manholes such as
- These are corrosion resistant.
- Fiberglass manhole are watertight.
- Can be coustmized into varity of shapes and strutures.
- Fiberglass has longer lifespan.
- These are extremly robust.
- These are light weight, which weighs 1/10th of concrete.
Also Read – Soak Pit – Construction| Design| Uses| Advantages and Disadvantages
Manhole Cover or Inspection Chamber Cover
A manhole cover is a removable(opening and closing) cover that acts as a lid to a manhole. The main purpose of a manhole cover is to prevent people or animals from falling into the manhole and it also serves other purposes like restricting unauthorized individuals from accessing manholes and also providing ventilation to prevent sewer or stormwater gases from entering residences.
Manhole cover act as an entry point for maintenance and repair works of manholes. a manhole cover is also known as an inspection chamber cover
Manhole Cover or Inspection Chamber Cover Materials
Manhole covers or inspection chamber covers are usually built with cast iron or concrete. These materials are less expensive, durable, and heavy enough to stay in place without moving. inspection chamber covers are usually removed using a manhole hook.
A manhole hook is equipment or a tool used to lift and replace the manhole cover safely.
With modern innovation and technology, Manhole covers are manufactured with different materials such as fiberglass, plastic, etc.
Periodic maintenance work is needed in order to avoid blockage or jamming of the inspection chamber, which may lead to several problems in sewer lines.
Some of the maintenance work you need to look into a manhole
- Ensure that no dead animals, roots, sediments, or vegetation are present in the manhole.
- Ensure that the inlet and outlet pipes are free from debris.
- Ensure that manhole cover is placed properly, securly and easy to remove.
- Check for any cracks or damges within the structure.
- Ensure that no pollutents are present in Inspection Chamber such as oil, gasolines, etc.
- The additional features like ladder and covers must be good, secure and according to stanadrd code.
Also Read – Wastewater Treatment Process | Why it is Important?
FAQ’s on Manhole
1. What tool is used to open manhole?
Ans – Manhole hook or manhole puller is used to open manhole.
2. How heavy is a manhole cover?
Ans – Based on the type of materials used to make a manhole cover the weight varies, but it will be more than 113kg.
3. What is a manhole called in UK?
Ans – Manhole is also known as Inspection Chamber.