Thanks Stewie
I agree they don't look as strong but engineers
swear by them, well some engineers, I know a couple who won't recommend them on highly reactive sites and they have lost work because of it.
Even if they are as strong there a other reasons why I would prefer raft slabs one of them as BE has said is water ingress under the slab
If I has the choice between rock and highly reactive soil I would go with to rock every time
Difficult and can be more expensive but when you finished the footings that's the end of it
you can sleep at night