Manholes with eccentric cones are probably the most common type of manhole used in most infrastructure projects. They are easier to place and provide more stability for maintenance. All you see is the manhole cover, usually found in the middle of the street, in parking lots, or other places where water might accumulate during heavy rains.
The reason you only see the cover is because that’s how big the opening to the manhole is. Once inside, the manhole widens to varying diameters, most widely used however are 48 and 60 inch. The diameter is dictated by the diameter of the pipes entering and exiting the structure, however, it primarily allows for enough room for maintenance activities to be performed. You could imagine that working in a 25-inch diameter tube wouldn’t be very comfortable at all.
Eccentric vs. Concentric
An eccentric cone features an opening at the top but is placed to one side of the cone. This makes it easy for workers to lower themselves into the manhole with rungs or a ladder while still increasing the diameter of the manhole for maintenance or service.
With a concentric cone, the opening at the top is placed in the middle. This means rungs won’t be added to help someone lower themselves down because they’d be placed at an angle. Not safe at all! With a concentric cone, a tripod with fall protection is used to lower a worker into the manhole.
Obviously, the eccentric cones are much easier for entering and leaving a manhole, but they also provide versatility when placing a manhole. If the manhole cover needs to be placed in a certain area, the cone can be rotated to avoid obstacles that may impede installation.
Advantages of Precast Manholes
Because of their dimensions, eccentric cones would be very difficult for a pour-in-place procedure. In fact, precast concrete is used most (if not all) of the time when it comes to buried infrastructure. They are easier to deal with at the job site because of how efficient they are for installation. Imagine trying to pour concrete for an inverted cone!
Aside from ease of use, precast is always going to be a more durable product. Made in a controlled environment, mixing, pouring, casting, and strengthening process can all be done in away from the elements, removing variables that can’t be controlled when being poured into place. That means precast can be used in all four seasons.
Made to Exact Specifications
No matter if you need a manhole for a private enterprise or public, Columbia Precast eccentric cone manholes are made to follow all codes and regulations. This includes the Washington State Department of Transportation strength standards as well as local municipality codes.
In addition to being one of the most naturally durable pieces of infrastructure, we’ll also protect your investment from the inside, too. At Columbia Precast, we make a point to be on the cutting edge of precast technology. That’s why we were the first buried infrastructure facility to earn SMaRT certification in the United States.
When you partner with Columbia Precast Products, you’ll be working with decades of experience, manholes that are ready when you are, and a company that works to be a good steward of the land. After all, we also live here! If you have a buried infrastructure project, contact us and see how we can help.