When Mat or Raft foundation is adopted?

Raft foundation is adopted for medium heavy structures in places where the soil has low bearing capacity.
It is also used where unequal settlement is suspected.

Raft foundation is mainly used when the bearing capacty of the soil is low , in such a case a solid reinforced concrete rigid slab is constructed under the entire building . Structurally , raft foundations develop the maximum availablr bearing bearing area under the building . Another advantage is their continuity and rigidity which helps in reducing differential settlement of individual columns .

Raft Foundation are constructed where the bearing capacity of the soil is low and the structure to be constructed is heavy (multistoreyed).

first, raft foundition can consist of a slab of a uniform thickness or a slab stiffened by a beams either above or below.

this type is useful where the columns load are heavy or the bearing capacity is low resulting in the need of large bases.

also , it is used where the soil mass contains compressible layers or variable so that diffrentail settlemnet would be difficult to control.

 

first thing the 

............second go and come tomorrow