On Sat, 02 Sep 2006 11:56:32 -0700, CanopyCo wrote:


Sheldon wrote:

Never install any wooden pole/post in concrete... it will heave and it
will rot. Set in gravel or sand or any material contribuing to good
drainage, then back fill with whatever soil was removed. Only metal
posts/poles get set into concrete, and even those should have good
drainage material at the bottom or they will heave. If your frost
penetration is 8' than you need to go at least that depth, especially
with wood.

What part does the frost line play?
I always thought the depts was determined by the leverage applied by
the pole.
What am I missing?

If you live where the ground seriously freezes in the winter, the earth
will essentially try to spit the pole out. (Look up "frost heave".)
Frost heave is why in areas with rocky soil, if one picks rocks one
year, there will be a new batch the next. And why in the olden days when
wood fence posts for barbed wire fence were driven, farmers went around in
the spring and re-drove any that had heaved.

Iirc the rule-of-thumb for leverage is 1/3 the length of the pole/post for
mid-range lengths; shorter more and longer less.