There are thousands of manhole covers across the country and most people don’t give them a second thought. Yet, these manholes provide access to a vast array of pipes that carry sewage away from your home and to the treatment plant. It’s a complex system that needs to be monitored and maintained to ensure it stays in good working condition.
It should be noted that manholes are not usually found on railway tracks as you don’t want the weight and vibrations of trains constantly disturbing and possibly damaging the sewer pipes below. That’s why, while the right railway equipment can help you move a sewer or manhole, it’s not commonly needed.
However, if you work in any type of construction you need to be aware of the different components that make up a manhole.
The Chamber
The chamber sometimes referred to as the ring, is the man piece of any manhole; It’s the circular pipe that provides access from the surface to the man sewer below. This pipe is a least a metre in diameter, allowing people to move inside it.
Manhole chambers are usually made of concrete which is prefabricated at the factory. They can be slotted together on-site to create the right depth, allowing access to the sewers.
Concrete bases
The manhole chamber is sat on a base of concrete and concrete is often pumped around the outside of the chamber to provide it with additional strength. This is important as vibrations from nearby traffic can cause soil to shift.
Again, concrete is usually poured on-site, construction is as simple as creating the framework and arranging the concrete delivery truck.
Sealant
Every manhole chamber has a lip on the top which allows the manhole cover to sit over the lip, ensuring that traffic can move over the top without issue. However, every cover also has to have sealant strips fitted around the ridge of the chamber. This ensures the manhole chamber is watertight. Treating water is expensive, the board doesn’t need additional rainwater and other products to deal with.
The Cover
Manhole covers are always made of metal as it’s strong and can be fabricated with recessed sections. These allow workers to position a tool and lift the manhole cover when needed.
Backfill
Smaller manhole chambers may not have concrete surrounding them, although this is obligatory if the chamber is more than 4.5m deep. If there is no concrete surround then the exterior of the chamber needs to be backfilled. This must be with a granular product to ensure the chamber isn’t damaged in the process.
Getting In & Out Of the Chamber
Some manhole chambers will have rungs built into them, making it easier for people to move up and down them. But, because of the depth that a manhole can be, in most cases there are several workers and one person is lowered into the chamber on a rope with appropriate safety features.
Only authorized people should ever enter a manhole chamber.
