Mr. Gunnar H. Isleifsson:
As Mr. Gilligan advices, it's recommended to check the piles for
some effect, but based in a fraction of the slab mass. You could design some
sort ok keys protruding from the slab to lock the slab and the soil in such
way that slab and soil always work together. Posibly more economical than to
design piles with the total mass effect of the slab.
W. Bassett A.