I recently moved into a new home in upstate New York which has a fence around the backyard. The fence is made out of some kind of metal and the fence posts are about 2" square. One of the fence posts had risen a few inches since it was first installed due to frost heave. It had been set in a concrete footing and the whole footing had risen. I have dug out and removed the concrete (by my estimates it had gone down 33±3") and now have a roughly 40" deep hole approximately 9" in diameter. The fence post itself only goes about 20" into the ground.
I haven't been able to find a solid answer on the frost line up here, but my plan was to dig down to around 42", place an 8" cardboard tube form, and fill it with four 50lb bags of quickrete and set the post in the footing.
My concerns are:
1) is this enough? I never want to have to dig out this concrete footing again, so if I'm going to use concrete, I want to make sure this is the right way to go. I'm using a clamshell post hole digger and at 40" deep it's getting harder to go any further.
2) is this overkill? Given it's only a 2" post going ~20" into the ground, would I be better off just setting it in gravel or crushed rock or something and tamping some dirt on top? Even if it heaves out of the ground again, it would be much easier to dig down and fix than if I had to dig out the 42" concrete footing.