Do you know what these are? Anyone? Anyone?
They’re manhole rings. Some people call them “donuts”.
Think of the manhole as a vertical tunnel, or a “chimney”. The manhole is the vertical access point to the underground sewer system. Sewers can be anywhere from 8 to 40 feet underground, so in order to access the lines for maintenance purposes, the maintenance workers remove the manhole lid that you see from street level and proceed down a ladder through the manhole shaft to the bottom of the manhole. From here they use other tools to clean out obstructions or to ascertain other problems.
Manhole rings are used to raise the top elevation of manholes. Specifically, these raise the top of the chimney so that it intersects with the ground surface at the correct elevation. The best example of this is when a manhole is in a road. We want the manhole to “daylight” into the road surface at precisely the correct elevation. Too high and it causes a bump in the road. Too low and it causes a pothole in the road. The manhole rings sit on top of the chimney of the manhole to get the top of the manhole to be at the same elevation as the road surface so that the manhole doesn’t create a problem for the driving public. Sometimes one ring will do it. Sometimes it takes more than one.
We care about manhole rings because they are a good example of how we integrate our systems. Manhole rings are a small, but important tool in integrating our concern for the safety of traffic using our transportation system with our concern for the environmental integrity of our sanitary sewer system.
The manhole ring is where safe transportation meets pollution control. Right there in the middle of a concrete donut.
