Apologies to Mr. Gabriel.
I'm installing a 4X4X16 pole for a clothesline. I'm down to about 3 feet and I
hit solid rock. Not 'a' rock - just rock. I'll be using 10" sonotube (I have 4'
of it) and concrete.
Any rules of thumb for how deep I *should* be for good lateral stability? I can
obviously cut the pole shorter, but I'd like to have 10'->12' above ground to be
somewhat level with the mounting point on the house.
I don't know the rules about this, but I've got 4x4s in my garden, down 2
feet *without* cement. 10 feet apart, clothesline running between the tops
for beans to run along. The cord's not pulled as tight as you would with
clothesline, but it seems to me that 4 feet with cement ought to be fine.
3 to 4 feet of concrete should provide plenty of lateral support for a
However, having 12' of 4X4 above ground without the top anchored (as it
would be in, say, a deck support) should produce some interesting curves in
the post over time :-).
You need to consider how deep the frost line is and whether the land
gets soggy in the Spring rainy season.
Concrete simply poured around the 4x4 doesn't provide much support. But
if you spread it out so it has a large horizontal flange around the
pole, that will provide more bearing surface. Of course, the concrete
has to extend down around the pole in a thick enough layer so the pole
doesn't twist out of it.
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