When we bought the house we were pretty sure that the foundation was built very poorly, and expected we'd eventually have to fix it. The floor was built on thick beams that were setting on wooden upright posts stuck into the ground. For the first 50 years it was fine, but as wood does, they were beginning to rot, and eventually we would've had big problems. There was no concrete in the entire foundation. So basically we took the floor, and formed and poured a new foundation around the entire perimeter. I'll have to write a post with photos showing the whole process.