Clay around concrete base for cottage on pillars

I installed a 3.5 foot deep concrete base to bedrock in clay soil to replace one heaving concrete pillar under my cottage. The concrete base is 30 inches square and has some rebar in it. I used the original clay ground as the form.

Will the concrete base heave in the winter months, it gets -30 C around here? Should I excavate one foot around around the new concrete base and out gravel or sand? There is no way to drain the base as it's install near the edge of the water on a lake. Or is it fine to leave the clay around the new concrete base? All my other pillars are on rock.