"My question is this, can a slab 4-6 thick slab properly support the superstructure?"

Forget the thickness of the "slab", think "thickness of the footing".

Does the "footing" meet the required thickness and width required by the code?

The answer is "No, it does not."

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Jerry Peck, Construction / Litigation Consultant
Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )