Types of manholes

What Is A Manhole | Purpose of Manhole | Types of Manholes | Manhole Construction Details11 min read

What Is A Manhole?

Manhole can be defined as an access point inside the sewer line for material and workers. It is the most important component of the sewer line because it completely eliminates the need for the digging process and it is also known as an Inspection chamber or Unit.

What Is A Manhole | Purpose of Manhole | Types of Manholes | Manhole Construction Details
Manhole

The main purpose of the construction of manhole is trenchless rehabilitation for the sewer system, an inspection of a drainage system, cleaning the clogged line, and maintenance purpose, also it is an initial step for entering the inside sewer line and finding out a problem on it and it also helps to replace the damaged pipe without need of digging work.

Manholes are placed throughout the sewer line at regular intervals till the end of the main sewer line or drainage point.

Generally, the ma nhole is consisting of a vertical circular chamber of different sizes and depths which is used to reach the inspection point.

Manholes construction is don at that point where the change direction of sewer line and gradient of a sewer line. The man hole is typically installed 0.5 m away from the curb line of the road.

Also, the ma nhole covers are available in different size, material, and shape such as rectangular, circular, and square; it is made from metal, precast concrete, and composite material.

If man hole chamber depth is more than 2.5 m then a ladder must be fitted inside and if the depth is less than 1 m then a step ladder must be used.

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Purpose of Man hole

  • For inspection purposes, maintenance purposes, and removal of any obstruction part present in the sewer line.
  • For connecting sewer line at a junction point.
  • For changing the direction or alignment of a sewer line.
  • For changing the gradient of a sewer line.

Types of Manhole

The following types of manholes are given below,

  • Shallow Man hole      
  • Deep Man hole
  • Normal Man hole

Shallow Manhole

A shallow manhole is constructed at the start of a branch sewer line and where there is no heavy traffic and it has a depth range from 75 to 90 cm.

Normal Man hole

A Normal Manhole has a depth of 150 cm and generally, it is square in shape with a heavy cover on its top surface.

Deep Manhole

A deep manhole is provided at greater than 150 cm with a heavy cover on its top surface. Also, the depth of the man hole is increased same as the facility for going down is increased.

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Component of Manhole

What Is A Manhole | Purpose of Manhole | Types of Manholes | Manhole Construction Details
Component of Manhole

The following are major manhole parts,

  • Access Shaft
  • Working Chamber
  • Base and Sidewall
  • Bottom or Invert
  • Ladder or Steps
  • Cover and Frame

Access Shaft

An access shaft is a vertical passage and upper portion of the manhole which provides access to the working chamber. The minimum size of the access shaft for a rectangular man hole is about 0.75m x 0.60m and for the circular shape ma nhole 0.70m diameter. In some cases, the access shaft may be covered by a reinforced cement concrete slab with a suitable dimension


Working Chamber

Working chamber means lower portion of the manhole which is provided working space for cleaning and inspection of the sewer line.

The minimum size of the rectangular chamber is 1.2m x 0.9m with the flow is provided larger side. The minimum size of the Circular chamber is 1.2m and the height of the working chamber should be not less than 1.8m.

Generally, the size of the working chamber is larger than the access shaft. So that the working chamber is constructed by enlarging the bottom area of the access shaft.


Base and Side Walls

Generally, the base of the manhole is made of plain cement concrete and it is placed at the base level, for supporting the sidewall of the ma hole and also it is preventing the entry of groundwater.

Minimum thickness of bed of concrete Depth of man hole
15 cmUp to 0.8 m
23 cmAbove 0.8 m to 2.10m
30 cmAbove 2.10 m

The manhole side walls are made of stone masonry, brick masonry, and reinforced cement concrete. But commonly used brick masonry as a sidewall.

Minimum Thickness of Manhole  Depth of Man hole
20cm up to 1.5m
30cmmore than 1.5m

The following rule may be used for determining the thickness of brick walls,

t = 10 + 4d……. (1)

Where,

t = Thickness of wall in cm

d = Depth of manhole in m

The outside brickwork and inside brickwork are plastered with the cement mortar 1:3 means 1 part of cement and 3 part of coarse sand and inside apply smooth finished cement coat.

The thickness of reinforced cement concrete walls will be much less than as compared to the brick walls. However, the R.C.C man hole wall is costly and is used in a special case.


Bottom or Invert

The bottom portion of the manhole is semicircular or U-shaped. It is a cement concrete channel also the diameter of the concrete channel is equal to the sewer line.

The horizontal diameter is extended vertically nearly up to the crown point of the sewer or man hole, and their top edge is rounded off and made to slop towards the channel to form benching.

For benching, the slope is provided from 1 in 10 to 1 in 6. When two or more sewer lines are entered into a manhole at the same level of the bottom portion of a manhole, so the main channel branch is constructed similarly with respect to the benching. At the junction point of the sewer line, easy curves are provided.


Steps or Ladder

Ladders are provided in that case when the depth of the man hole is more than 0.8 m. These steps are made of cast iron and placed inside the man hole; also the arrangement of a ladder is staggered type.

The distance between the two steps is 38cm center to center horizontally and vertically 30 cm center to center.

The width of all ladders is 15cm and the first ladder is placed 45cm below the cover of the man hole and the lowest ladder is not placed more than 30 cm above the benching level. these steps are sufficiently embedded in the chamber wall so that they do not overturn.


Cover and Frame

The top open portion of the manhole is close to the set of frame and cover, generally, the opening of the man hole is in a circular shape so that the cover of the man hole is a circular shape. The standard size of the cover is 56cm in diameter and the depth is more than 0.9.

What Is A Manhole | Purpose of Manhole | Types of Manholes | Manhole Construction Details
Cover and Frame

Both the frame and cover are made of cast iron, frame is supporting the cover also the weight of the cover is varies from 90 to 270 kg.

The heavy type cover and frame is adopted where heavy traffic load is to be borne and similarly the light type is adopted for light traffic load is to be born.

The frame is slightly embedded in the concrete surface on the top of the wall and the cover is placed in the groove which is provided inside the frame. To avoid becoming top surface is slippery so that make the rough surface of the man hole cover.

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Materials Used for Construction of Man hole

The following types of material are used for the construction of manholes,

  • Plastic Man hole
  • Pre Cast Man hole
  • Fiberglass Man hole

Plastic Manhole

What Is A Manhole | Purpose of Manhole | Types of Manholes | Manhole Construction Details
Plastic Man hole

Plastic man holes are manufactured by using polyethylene material. It is environmentally friendly and sustainable and also does not ill effect the soil or the ground where it is placed.

The main advantage of using plastic ma nholes is they do not require frequently rehabilitation and maintenance.


Precast Concrete Man holes

What Is A Manhole | Purpose of Manhole | Types of Manholes | Manhole Construction Details
Precast Concrete Manholes

Precast concrete manhole is a traditional method for the construction of a man hole. This method is easy to install and easy to assemble on the site. Also, its life span is high so that it is a more popular type of manholes.


Fiberglass Manhole

Fiberglass man hole is having additional features like grinder channel, weirs, separation unit for stormwater, etc.

What Is A Manhole | Purpose of Manhole | Types of Manholes | Manhole Construction Details
Fiberglass Manhole

The fiberglass man hole is easy to handle and place. Its weight is much less than as compared to concrete man hole. Also, it is environmentally friendly and highly durable in nature.

Read More: Methods of Rainwater Harvesting | Rooftop Rainwater Harvesting | Rainwater Harvesting Method


Types of Manhole Cover

The main aim of providing a manhole cover, it serves as a lid to close the man hole also that cover is removable .generally man hole cover is made of concrete, cast iron, and a combination of two. These materials are commonly used because it is inexpensive, more durable, and heavy enough to stay in place properly.

Due to modernization ma nhole covers are available in various materials like fiberglass, plastic, and composite, etc.


Ductile Iron Cover

What Is A Manhole | Purpose of Manhole | Types of Manholes | Manhole Construction Details
Ductile Type Manhole Cover

Ductile type manhole covers are made of ductile iron and nodular iron it is a unique form of iron. This type of cover is more popular due to its strength, solidness, durability, and resilient features. A ductile man hole cover will not corrode as quickly as a cast-iron man hole cover.


Recessed Man hole Cover

What Is A Manhole | Purpose of Manhole | Types of Manholes | Manhole Construction Details
Recessed Manhole Cover

Recessed manhole cover as the name suggests it is placed in recessed areas suitable for laying paver block, cement, and a layer of screed for aesthetic appearance in a pedestrian way.

These types of man hole covers are more suitable for internal man holes such as workshop, hospital, domestic, and garden apartments.


Solid Top Cover

What Is A Manhole | Purpose of Manhole | Types of Manholes | Manhole Construction Details
Solid Top Manhole

Solid Top man hole cover is made of lighter galvanized material and is designed to be prominently visible on the floor.


FAQs:

What is a Manhole?

Manhole can be defined as an access point inside the sewer line for material and workers. It is the most important component of the sewer line because it completely eliminates the need for the digging process and it is also known as an Inspection chamber or Unit.

What are the types of manholes?

The following types of manholes are given below,
Shallow Man hole      
Deep Man hole
Normal Man hole

What is the Purpose of Manhole?

  • For inspection purposes, maintenance purposes, and removal of any obstruction part present in the sewer line.
  • For connecting sewer line at a junction point.For changing the direction or alignment of a sewer line.
  • For changing the gradient of a sewer line.
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    Post Contents What Is A Manhole?Purpose of Man holeTypes of ManholeShallow ManholeNormal Man holeDeep ManholeComponent of ManholeAccess ShaftWorking ChamberBase and Side WallsBottom or InvertSteps or LadderCover and FrameMaterials Used for …

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