We just put up a 15'x25' woodshed for an old fella up the road. He had us use 16' 6x6 PT posts set in crushed limestone. Then he dumped old motor oil on top of the stone. The next day the stone had settled 3-4inches and there was NO movement in those posts. Claims that he used to do this on all his pole barns. Every few years he would add a bit more oil. Frost never moved anything either
not something I would ever post on a public forum, highly illegal to dump waist oil! EPA toxic waste cleanups start at 1 gal and a crazy expensive.