Structures underground experience buoyant forces that act to push them up. Manholes (and any structure bottom, like storm inlets, pump station wet wells, etc) need special consideration since they can be partially or mostly hollow, so they have to be heavy enough to remain in place.
Technically it’s the manhole covers that need to support the weight.
Manholes themselves are expected to do the opposite of holding weight
They hold light?
It’s dark inside so of course the light is held □
Structures underground experience buoyant forces that act to push them up. Manholes (and any structure bottom, like storm inlets, pump station wet wells, etc) need special consideration since they can be partially or mostly hollow, so they have to be heavy enough to remain in place.
You know, I knew that but couldn’t figure out what the opposite of weight was for some reason. Thanks for the extra learning!
Fun fact: Coffins experience this force too, and during flooding can rise up out of the ground
Ah, that explains why my grandpa was buried in a lead coffin.
He lost a lot of weight right before he died, so he was too light!