Types of Manhole | Material Used in Manhole Construction | Types of Manhole Cover
In this article, we will discuss the various types of manholes, materials used in manhole construction, the purpose of manholes, and types of manhole covers.
What is Manhole?
A manhole, also known as a utility hole or maintenance hole, is a covered opening in a road or sidewalk that provides access to underground utilities such as sewage systems, storm drains, electrical conduits, or telecommunications infrastructure. It is typically a large, round, or rectangular hole with a removable cover made of metal or concrete.
Manholes are essential for maintenance and inspection of underground infrastructure. They allow workers to enter and access the utilities below the surface for repairs, cleaning, or installation of new equipment. Manholes are usually located at regular intervals along streets and sidewalks to provide convenient access points.
The covers of manholes are designed to be sturdy and secure, ensuring safety for pedestrians and vehicles that pass over them. They are often marked with specific symbols or text to indicate the type of utility they access, such as “Sewer,” “Electric,” or “Telephone.”
It’s important to exercise caution when near manholes, as they can present hazards such as open holes, slippery surfaces, or dangerous gases in some cases.
Purpose of Manhole
The main purpose of manholes is to provide access to underground utilities for maintenance, inspection, and repairs. Here are some specific purposes of manholes:
Maintenance and Repair
Manholes allow workers to enter the underground infrastructure to perform maintenance tasks, such as cleaning out sewer lines, unclogging drains, or repairing electrical cables. The access provided by manholes simplifies the process of locating and addressing issues within the underground systems.
Inspection
Manholes serve as access points for inspection of underground utilities. Workers can lower cameras, sensors, or other inspection equipment into the manholes to assess the condition of pipes, cables, or other components. This helps identify potential problems, such as leaks, cracks, or blockages, which can be addressed promptly.
Installation and Upgrades
When new utility lines or equipment need to be installed, manholes provide entry points for workers to carry out the installation process. They allow for the placement of cables, pipes, or other infrastructure underground and enable connections to existing systems.
Access to Underground Systems
Manholes provide access for workers to reach underground systems for various purposes. This includes tasks such as reading utility meters, conducting tests, or making adjustments to equipment.
Safety and Emergency Situations
In emergency situations, such as gas leaks or flooding, manholes provide points of access for emergency response teams. They can quickly enter the underground systems to address the situation and ensure public safety.
Types of Manhole
There are several types of manholes that are commonly used based on their specific purposes and the utilities they provide access to. Here are some of the main types:
Normal manhole
A “normal” manhole typically refers to a standard or typical manhole structure that is commonly used for accessing and maintaining underground utility systems.
Normal manholes serve as access points for various underground utility systems, including sewer lines, stormwater drains, telecommunications cables, electrical conduits, and more. They provide a means for workers to enter and carry out necessary tasks while also protecting the underground infrastructure and ensuring the overall efficiency of the utility system.
Shallow Manhole
A shallow manhole refers to a manhole that has a relatively shallow depth compared to standard or deep manholes. While there is no fixed definition of what constitutes a shallow manhole, it typically refers to manholes that are constructed at shallower depths, usually less than 2 meters (6 feet).
Shallow manholes are commonly used in situations where the depth of the utility lines or infrastructure does not require a deep excavation.
It’s important to note that shallow manholes should be designed and constructed following local codes, regulations, and engineering standards to ensure structural integrity, safety, and functionality. The specific design and dimensions of a shallow manhole will vary based on the site-specific requirements and the utility system it serves.
Deep Manhole
A deep manhole refers to a manhole structure that has a significant depth compared to standard or shallow manholes. Deep manholes are typically used in situations where utility lines or structures are located at greater depths or where access to deeper underground systems is required.
Deep manholes play a vital role in providing access to underground utility systems at significant depths. They allow for inspections, repairs, and maintenance to ensure the proper functioning of utility networks. The design and construction of deep manholes follow engineering standards and local regulations to ensure their stability, safety, and longevity.
Components of Manhole
A manhole consists of several components that work together to provide access to underground utilities and ensure the safety and functionality of the structure. Here are the common components of a manhole:
- Access Shaft
- Working Chamber
- Sidewall and Base
- Bottom or Invert
- Ladder or Steps
- Cover and Frame
Material Used in Manhole Construction
- Precast Concrete Manhole
- Plastic Manhole
- Fiberglass Manhole
Manhole made of Precast
Precast manholes are commonly used in construction due to their efficiency, durability, and ease of installation. Precast manholes refer to manholes that are constructed using precast concrete components. Instead of casting the entire manhole on-site, precast manholes are manufactured in a controlled factory environment and then transported to the installation site for assembly.
Advantages of Precast Concrete Manholes
Precast concrete manholes offer several advantages. They are highly durable and can withstand heavy loads and harsh environments. The controlled manufacturing process ensures consistent quality and uniformity. Precast manholes are also resistant to corrosion, chemicals, and other environmental factors.
Durability and Strength: Precast concrete is known for its strength and durability. It can withstand heavy loads, resist corrosion, and provide long-term structural integrity. This makes precast manholes suitable for various applications, including high-traffic areas.
Manhole made of Plastic
Manholes made of plastic, particularly High-Density Polyethylene (HDPE), are increasingly being used in certain applications due to their numerous benefits. High-Density Polyethylene (HDPE) is a thermoplastic material that offers excellent chemical resistance, durability, and flexibility. HDPE plastic manholes are manufactured through a molding or fabrication process using HDPE sheets or panels.
Advantages of Plastic Manholes
Plastic manholes have several advantages. They are lightweight, making transportation and installation easier compared to heavier materials like concrete or cast iron. Plastic manholes are also corrosion-resistant, which makes them suitable for applications where chemical resistance or exposure to corrosive environments is a concern.
Durability and Longevity: HDPE plastic manholes have a long service life and are resistant to cracking, corrosion, and impact. They can withstand a wide range of temperature variations, making them suitable for various climates. The inherent durability of HDPE ensures a robust and long-lasting solution.
Manhole made of Fiberglass
Manholes made of fiberglass reinforced plastic (FRP) or fiberglass composites are commonly used in specific applications where corrosion resistance, lightweight construction, and durability are required. Fiberglass is a composite material composed of a polymer matrix reinforced with glass fibers. FRP manholes are manufactured by molding or fabricating layers of fiberglass and resin into the desired shape and size.
Advantages of Fiberglass Manhole
One of the primary advantages of fiberglass manholes is their exceptional resistance to corrosion. Fiberglass does not rust or corrode, making it suitable for environments with harsh chemicals, wastewater, or corrosive elements. This corrosion resistance extends the service life of the manhole and reduces maintenance requirements.
Durability and Longevity: FRP manholes exhibit excellent durability and resistance to cracking, impact, and UV radiation. They can withstand various environmental conditions, including temperature fluctuations, moisture, and aggressive chemicals. Fiberglass manholes are known for their long service life and low maintenance requirements.
Also Read: Box Culvert Reinforcement Layout | Types of Sewer Pipes | Plumbing Tools
Types of Manhole Cover
There are various types of manhole covers, designed to meet different requirements based on their location, purpose, and load-bearing capacity. Here are some common types:
Ductile Iron Manhole Cover
Ductile iron manhole covers are a type of manhole cover made from ductile iron, also known as nodular cast iron or spheroidal graphite iron. Ductile iron is a type of cast iron that is engineered to have enhanced strength, toughness, and flexibility compared to traditional cast iron.
Ductile iron manhole covers are widely used in infrastructure projects, including roadways, highways, parking lots, and industrial areas, where their strength, durability, and resistance to heavy loads are essential.
Recessed Manhole Cover
A recessed manhole cover is a type of manhole cover that sits lower than the surface level of the surrounding area. Unlike standard manhole covers that sit flush with the pavement or ground, recessed covers are designed to create a recessed or lowered area around the cover.
Recessed manhole covers are commonly used in urban areas, sidewalks, pedestrian zones, car parks, and other locations where maintaining a smooth and safe surface is crucial. They provide access to essential infrastructure while minimizing potential trip hazards and maintaining aesthetic appeal.
Solid Top Manhole Cover
A solid top manhole cover is a type of manhole cover that has a completely closed and solid surface, without any openings or perforations. Unlike other types of manhole covers that may have slots, holes, or grates for ventilation or drainage purposes, solid top covers provide a sealed and secure barrier.
Solid top manhole covers are commonly used in various applications, including roads, highways, pedestrian areas, parks, and areas with strict safety or containment requirements. They are particularly suitable for situations where protection against debris, containment, or a smooth walking/driving surface is essential.
