What is raft foundation?

Raft or mat foundations

• Raft foundation is also known as Mat foundation. Definition of raft foundation along with working principle, when to choose raft, types of raft foundation, materials of raft foundation, raft construction steps etc are discussed below.

• In case of made-up grounds, soft clay or marshy site or in case of the possibility of differential settlement, the usually spared footing, will not be suitable. In such case, it is wise to excavate over the entire area of building for its foundations.

• Raft foundation is a thick concrete slab reinforced with steel which covers the entire contact area of the structure like a thick floor. Sometimes area covered by raft may be greater than the contact area depending on the bearing capacity of the soil underneath.

• Generally, the R.C.C of suitable thickness is laid over the entire area of building in the form of raft or mat and is therefore known as raft or mat foundation. It is so designed that the allowed bearing power of the soil is exceeded. If required, beam and slab construction in R.C.C can also be carried out.

• The raft is designed as an inverted R.C.C roof with a uniformly distributed load of the soil pressure and supported by walls, beams, and columns. Also, if there is any fear of grounds water suitable holes should be provided in the raft to release the pressure of water.