PT ground slab cracked

[Dansmithpe]

I recently looked at a PT foundation slab supporting a 3 story building. The footiprint is rectangular but necks down at the middle. At the middle there is a 1/2" wide crack through the 4" slab (from front to back). Buidling is 5 years old, on clay with excessive water around the foundation. Have not accessed the top of the slab yet. No sign of broken cables. I suspect settlement. Anything else I should look for ?

 

[casseopeia]

what about the possibility of expansive soils?

 

[AlohaBob]

I think it would be worthwhile to model this structure with it's foundation and soil interaction. A 4" PT slab just doesn't have the stiffness to transfer loads excepting to a rock foundation without excessive deformation.