I've been thinking about the same foundation design for a frame one story house that you did for your cabin; my climate zone and soil conditions are pretty much similar (clayey, muddy soil freezing depth 1.5 - 2 m). Most professional builders suggest I should do piles to below freezing level ( either cast in place concrete, hammered or metal screwed). However some neighbours have pads above freezing level, do some shimming once a year and dont complain much about up/down movements. Hence my questions. 1) Did you come up with this design by yourselves or did you see it already done somewhere? Was it described it any building code? What codes did you use? Was it approved by local building authorities? 2) About calculations. Which calculations were done in addition to the size of the footing, soil's bearing capacity, what about lateral and bottom heave forces? 3) About rebar reinforcement of the pads. If pads depth is half its width, with such geometry can I go without reinforcement ( by placing those boulders into the mortar thus increasing volume of pads)?
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