I have a 20' x 32' cabin in NY state that was built on grade. Frost heave is tearing the drywall apart and shuffling the cabin down the mountainside.
I will be putting a pier foundation under it this summer. A test hole (protected from runoff) shows that the water table varies between 4 inches and 1 foot below grade, with a pure clay soil. I would like to use sonotubes for the pier forms, but the adfreezing/heaving problem might call for truncated pyramidal plywood-formed concrete piers. I am told that the pyramid shape would allow the wet freezing clay to detach from the piers as the soil expands and heaves.
I have these questions:
1. I would use sonotubes instead of plywood forms if I could find a foam product with which I could wrap the sonotubes so that the freezing clay would be unable to get a grip on the piers. The foam would have to be food grade as the well is just a few feet away. Is there such a thing?
2. Would the foam need to be in contact with the sonotube, or would it be enough to build a blue construction foam box around the sonotube pier to absorb the expansion?
3. Is blue foam elastic enough to return to its original thinckness once compressed?
4. Given that there is near zero drainage through the soil, is there any benefit to backfilling with granular fill instead of the clay from the excavation?
Big Papa G