Expert: Jeanette A - 10/4/2008

Question
Hi I am basically a mechanical engineer and getting involved with some civil activities. i would like to know what is mean by Raft foundation and what is the application of it and what are all the consideration to design raft foundation?

Answer
Hello Karthick,

Basically a raft foundation is type of shallow foundation. Shallow footings are used when the surface soil is quite strong and stiff as it can withstand the imposed loads.

Raft foundations spread loads from a structure over a large area usually the entire area of the structure. They have a slab extending over the entire loaded are which can be stiffened by use of ribs/beams in the foundation.

Used when column loads/structural loads are close together making individual pad foundations inappropriate as they would clash. They reduce differential settlement because the slab is able to resist differential movements between loading positions.

Mainly used on soft/loose soils with low bearing capacity as they are able to spread loads over a large area.


Hope that answers your question.

Warm Regards,
Jeanette