I would design it all as a single mat/raft with thickened areas under the columns (if you need them - make sure you check punching shear). Model the column and wall foundation loads as loads on the slab. And model the hydrostatic uplift as a uniform load…

Hi Alex, Here's my understanding of the situation: There's about 300psf hydrostatic uplift on the slab, which is fairly constant (and much greater than the slab dead and live load) The total column and wall loads far exceed the total hydrostatic…