I had to follow VDOT specs for my culvert too, which meant digging down about 4" below the bottom of the pipe and building up a bed with crusher run, etc, etc, etc. It's like the cadillac of culvert installs now, but jeez it was tedious.
Sounds like they are moving fast on the framing. Glad to see them using I-joists for your floor; I think they're superior to traditional lumber myself, though our builder preferred using 2x10s, which shrank a teeny bit over the first couple years. I have not seen lumber used for the main carrying beams in a long time though -- most use steel for that nowadays so there is no settling when the wood dries out. Keep an eye on those in the future -- might need to shim up with steel plates if the wood shrinks over time.