I do as well. I do remember people stating that areas appeared slightly sagged lower than others, and cracking around columns in those areas. It could be the concrete itsself that failed due to inconsistencies in the concrete's mixture. Also, it may have settled and/or hardened wrong, before, or after other areas, causing structual deformities, and the eventual collapse. i'm no expert or anything, but I'm highly sure it has to do with the concrete itsself, and not the soil.