DOUBLE SUBGARDE IN CSI SAFE

[Tstruct]

A structural consultant in my area uses CSI SAFE version 8 to design foundations. He has designed a lot of mid & low rise buildings for the last 40 years. I want to discuss a method he uses in SAFE. What he does is he draws 2 areas for foundation above each other with the lower one having a little offset (otherwise SAFE doesn’t recognize these areas as separate and deletes one). Now he assigns modulus of subgrade to both of them. The benefit which comes out of it is very huge. Soil pressure reduces by a significant amount. In 20-25 stories buildings where other engineers would use pile foundation, he provides mat foundation. Later versions of CSI SAFE don’t do this. There is no reason ever came from him, he only says I do this to double the springs. I never understood any logic behind this method. Does anybody here know anything about this method? See the attached photos where I tried to show the method.