Apology for wrong attachment. Link to the picture is as follows: https://docs.google.com/document/d/1PRt7P1WdvPdmtr...

According to my understanding

Risa foundation can only model the geo-technical aspect of the foundation (bearing capacity failure, settlement, overturning) using base area and loading of this footing irrespective of the shape above it.

To do the structural analysis of the footing we need to use Risa 3D or Risa footing.

I might be horribly wrong here, so please correct me.

Based on your descriptions, I would suggest that RISAFoundation is probably the program best suited for your needs. However, it is not really set up to handle varying thickness slabs as shown in that picture. So, if you wanted to approximate the slab as a slab of constant thickness then Foundation would be best.

If is crucial to model the thickness changes and such then you might have to use RISA-3D as it will give you more control over the plate elements used to model the foundation. The draw back is that it will not perform an overturning / sliding check. That would have to be done by hand. Same thing with the bearing capacity and the concrete design of the slab.

For those reasons, I would probably start out using RISFoundation. You can locally thicken a slab in some regions. So, those tools may be effective in modeling some of the thickness changes. Either that or draw in multiple adjoining slabs. That should be fairly easy, but if you use multiple slabs then the sliding and overturning checks would have to be done by hand.