I'm going to put a pier in my yard so that I can keep my mount mounted, and polar aligned, all the time. I will be covering it with a Telegizmo 365 cover. I suspect that I'll bring the ota inside the house most of the time, but it will be nice to leave it mounted when the weather cooperates for more than a day or two. I'd love to build an observatory, but that's not in the cards right now.
I think I read somewhere, and I can't find it now, that there should be a 10:1 weight ratio of the loaded mount (mount + ota + other stuff) to the base (underground) part of the pier. Using a combined weight of 150lbs for the mount would mean that the base should be 1,500lbs. That's 25 60 lbs bags of concrete. Using 0.45 ft^3 for a 60lbs bag of concrete yields 11.25 ft^3, or a cube with 2-1/4' (or 27") sides.
Is the 10:1 weight ratio correct? If not, what should it be?
The other question I have is: how long do you let a concrete cube cure before you cover it (with dirt) and put a load on it?
FYI: I'm still deciding whether to use concrete or metal for the above ground portion of the pier. I took a welding class at the local junior college and don't have any real concerns about fabricating a metal column with gussets and flanges (or pouring a concrete column).