What is floating foundation?

Floating Foundation:

Raft or mat is also recommended when the soil mass contains compressible layers or the soil stratum is variable. In such cases use of raft tends to eliminate differential settlements. The contact stresses are transferred to deeper depths since rafts are larger in dimension than footings. This may increase the total settlement in highly compressible soils. However this can be taken care of by making the weight of the structure and the raft approximately equal to the weight of soil excavated. Hence the net increase in pressure causing settlement will be reduced. This type of foundation is called Floating Foundation.