While manholes are used for a wide variety of applications, they are commonly used as part of a sewer or stormwater system. Manholes serve a few purposes in that capacity, either as a junction point where lines branch off as well as entry points for workers to investigate issues.
The 72-inch manhole is one of the larger manholes Columbia Precast produces on a consistent basis. The base segment of the manhole can be made anywhere from two feet high to eight feet high. Subsequent sections stacked on top can be made from one foot to eight feet tall.
The flattop of the manhole is eight inches thick and topped with either a standard 7-inch cover or suburban 3-inch cover. Grade rings of 2-, 3-, 4-, and 6-inches are also available for final adjustments. Gaskets and mastic can be used between the section and cover joints to provide water-tight seals. Click here to download a .pdf of the manhole.
Manholes can be equipped with two different bottoms: monobase and Perfect Base. The monobase is good for dry applications or water that is relatively free of debris because they are flat. The Perfect base is better equipped to handle sewer and stormwater systems because of the channels that are part of the base.
These channels are made to match up perfectly with ingoing and outgoing lines to provide an uninterrupted flow. This way debris in the system doesn’t get snagged, build up, and cause blockages. In the past, a worker would need to go into the manhole with concrete and make the channels by hand. Which was an improvement over the monobase, but still led to snags.
The reason precast concrete is used for manholes is because of its unmatched durability and longevity. Resistant to decay, fires, or animal infestations, our manholes are build to last for up to a century. However, we strive to be better at Columbia Precast, so we now offer antimicrobial additives to our sewer manholes.
What does this additive do? If sewage isn’t free-flowing or left stagnant, it can create hydrogen sulfide. This substance interacts with moisture in the air to create acid-generating bacteria. This bacteria can be corrosive to concrete. This is known as microbial induced corrosion or MIC.
These antimicrobial additives make it so the surface of the concrete repels this bacteria. It can be added during the mixing process or after the pieces have been manufactured. They can also be colored to make it easy to distinguish between untreated and treated manholes.
In some jurisdictions, this additive is mandatory. And why not? Making a great product that much more durable makes sense. Have an upcoming project requiring a series of manholes? Contact Columbia Precast and see how we can help. We have worked extensively with both ODOT and WSDOT codes and build all of our products to meet or exceed their requirements.
72″ Manhole – With Flat Top