The holes under sewer covers are round because it can withstand the pressure of the surrounding cylindrical land. Moreover, the sewer manhole means there are enough space to set person through , and people climb down a ladder along the cross-section who basically is round. So naturally circular shape become sewer manhole . Some will see a square lid on a square hole. This cover with surrounded rungs is larger than entrance. Usually the cover is made of metal , very heavy. We can imagine a square hole is two feet wide , 1 to 1.5 inches wide rungs .When sewer covers fall into , you need to lift one end , then rotate 30 degrees so that it is not hampered rungs , and then covers a 45 degree angle with the horizon , then shift the center of gravity was enough to make the covers fall. The circle has no such concerns. From the engineering point of view, the shape of the covers entirely depends on the shape of the hole.
Why are most sewer covers are round? Please check the following advantages.
- Save material
- Easy to transport
- Easy to install
- Force uniform
- Lid and wellhead are round , so the lid do not go off.
The sewer covers with Other shapes including square , rectangular , diamond and other types of quadrilaterals are easy to fall into the manhole. Vehicles and pedestrians on the covers any time through the use of round, mainly on account of circular covers through its center of each diameter are the same length , so that if the vehicle rolled through the covers to be played , because no matter how rolling onwards, will be slightly wider than the diameter of the wellhead below , covers not fall into the wellhead to go. And if using a square because the square was significantly longer than their diagonal length of each side , so the covers were rolled on, it is easy to fall into the wells diagonally wellhead , causing a safety hazard. Some people might ask , if the wellhead made of round or significantly less than covers, square manhole cover will not fall into the well. Here it involves a maximum material utilization and conservation issues . The use of wellhead depends on the wellhead size , if you have to install a square manhole cover much larger than the wellhead, then the use of natural materials and practical value is not good as the circular covers more efficiently. Round sewer covers not only save materials , but also ensure the safety of the wellhead.