Same crappy dirt here. Caissons and over excavate the crappy dirt and replace with engineered and compacted fill before your plumbing and concrete floors are installed. Same way with the backfill.
I previously lived in N Illinois...you could take your foundation down 40 inches and below the freeze line into undisturbed clay and you were good. Here (KS/MO border) there is the same explansive clay/soil mix overlaying limestone rock. (In a lot of places.) They had to blast to get deep enough for my sewer line, although I can't imagine them going to that cost and trouble for the foundation. (Cheap was not putting washers and bolts on the anchor bolts to secure the sill plate on my house. The attitude of some builders was: "Whats your house going to do? Get up and walk around?" No, of course not, but it does fly a bit when its hit by 120 mph wind and drop down on the occupants who are huddled in the basement. I did what they did not and put the washers and nuts on every exposed foundation bolt.
(Ok. so basement /storm shelter slide is over.)