Fill around support posts - dirt or rock?
I'm replacing some rotten support posts under our mudroom (formerly a porch, that someone enclosed years ago), which sits 3-4' above ground. After I've replaced the supports we will be regrading the yard, filling in that area 3-4' deep and covering the new posts.
1) I'm pouring footings on top of untouched ground, but I'm concerned about lateral support from the fill. I won't have room to get a compactor around the posts underneath the mudroom. Should I fill that area with gravel or other rock-based product for sufficient lateral support?
2) I'm torn between pressure treated posts (attached to galvanized saddles set in the footers) vs. concrete tube pillars. I'm not a big fan of creating problems for someone 20 years down the road when the pressure treated posts need to be replaced. If the answer to question 1 is "use gravel or rock," digging out those posts could be a real nightmare. But the tube pillars are more work and money.
Any thoughts would be very welcome!