Frost jacking forces are very difficult to predict, they depend on soil types, availabilty of groundwater, depth of freeze, rate of freeze, adfreeze bond of soil to object, etc. They can be very high, even 100 psi. A 'rule of thumb' in cold regions is to embed a pile below the frost depth twice the frost deth thickness - so if frost can penetrate 5', embed pile/post 15'. Same concept with piles in permafrost. You can mitigate the frost jacking forces by replacing soil in the seasonal frost layer with non-frost susceptible soil; lay subgrade insulation board to reduce the depth of frost penetration, use piles coated with epoxy paint to reduce the adfreeze bond, etc. If possible use some type of anchor, such as a bell, below the frost zone.
Hopes this gives you some ideas!
Carl
