may i know why we used raft foundation?

Question

why we used in detail of architecture and engineering.

Answer 1

Ok I'm not sure about the terminology here but I assume by raft foundation you mean a spread concrete footing. These are used where you have stable soil, (Not expansive clays). The purpose is the spread out the load on the foundation so that the pressure exerted by the building on the soil will not exceed the soil bearing capacity.