OK, for what its worth, I just got back from the bridge site with the contractor who MAY make the install of the four pilings. What he says is the traditional solution for sheering the ice at the piling is to wrap the piling with hemp rope. It seems to me I have seen a lot of pilings around piers before. I never looked close at the water line but apparently that's at least partially why the rope is there. This may be worth a try. It's cheep and easy to do.
Another consideration regarding ice lift occurs when the pond might freeze at a lower level, and then continues to fill during a January thaw (lets say) and lifts the entire ice sheet. This would be in addition to the normal expansion of ice as it freezes.
The contractor say 4' to 5' depth in the clay should be sufficient to reach the "hard pan". He uses air hammers to make the install and just keeps going till the piling wont go any further. They will use 16' - 4"x6" to do the job. Waiting for more ice however.
I'll attach some pics when it happens.
