So what’s your point?

Cylindrical or conic section, the same engineering principal applies.

To answer Greg’s question, manholes are cylindrical to better resist the compressive forces against the sides of the shaft. This was especially important when sewers and manholes were made of brick rather than re-enforced concrete.”

I dunno about your manholes, but our manholes are not the same diameter all the way down, and the access hole (the bit with the cover) is frequently significantly smaller than the rest of the hole.

For manhole, I like utility access hole best. But if I’m putting one on a landscape plan, I’d better use the term manhole or readers may not realize what I’m referring to.

I think the term manhole has lost most gender connection. As a woman, it doesn’t bother me much. Now, “Men Working” signs sure does. The landscape company where I used to work ordered some signs saying that and I vociferously suggested they change it to crew working. I’m not sure they did.

DC, the Reuleaux polygons (other than circle) do not fit tight in any orientation, only in a limited number of orientations.

Which is either good, bad, or unimportant depending on external considerations. On the other hand, they’re cheaper to make, which is always important. (NB: I referred obliquely to the “all orientations” with the “in use” note.)

Manhole covers are round because it is the only shape that has no possibility of falling into the hole on any orientation and it also fits tight on any orientation.

Posted by: NewEnglandBob

Sorry Bob, You answered the wrong question, and you even answered that question incorrectly.

Circular manhole covers are discs for only one reason: To fit circular manholes.

To answer Greg’s question, manholes are cylindrical to better resist the compressive forces against the sides of the shaft. This was especially important when sewers and manholes were made of brick rather than re-enforced concrete.

Manhole covers are round because it is the only shape that has no possibility of falling into the hole on any orientation and it also fits tight on any orientation.

Sorry, Bob, but ’tain’t so. That’s what the whole point was regarding Reuleaux polygons. Look them up.

If a manhole cover gets blown 50 feet in the air, that is a limited and known impulse. It would be a relatively trivial effort to tether the manholes so they don’t go more than 5 feet or so in the air. That would be enough to vent the explosion, but not enough that when the manhole came down it would kill anyone.

The most straight forward way would be to just put multiple heavy chains and not even attach them to anything. If the weight of the chains equaled the weight of the manhole cover, the height would be halved. You could attach chain weights equivalent to the estimated magnitude of the height.