Various types of Raft foundation
used depending on the condition of soil and the load
transfer mechanism on the foundation.
Followings are the different
types of raft foundation used in construction:
thickened under the column
beam and slab Raft
Frame Mat or Cellular Raft Foundation
Different types of mat foundation
are briefly discussed below.
1. Flat Plate Mat
This is the simple form of raft
foundation used when the columns and walls are uniformly spaced at small
intervals and subjected load are relatively very small. Reinforcement is fixed
in both directions and more reinforcement is required at the column locations
and load bearing walls. The thickness of this types of raft foundation is
generally restricted within 0.3 m for economic reason. A thicker slab would not
be very economical.
2. Plate Thickened under Columns
When the columns and load bearing
walls are subjected to very heavy load, the slab is thicken under the columns
and walls also the extra reinforcement is also provided to resist against
diagonal shear and negative reinforcement.
3. Two-way Beam and Slab
In this type of
foundations beams are cast singularly with the raft slab which is
connecting the columns and walls. This type of raft is suitable when the
columns are placed at a larger distance.
4. Plates with Pedestals
In this type of foundation, a
pedestal is provided at the base of the columns. Purpose of this type of
foundation system is same as flat plate which thickened under columns.
5. Piled Raft
This type of raft foundation is
supported on piles which is used when the soil at a shallow depth is highly
compressible and the water table is very high. Piles under raft always help in
reducing settlement and provides more resistance against buoyancy.
6. Rigid Frame Mat/Cellular Raft
In this type of raft foundation
act as a deep beam where rigid frame mat is referred when columns carry
extremely heavy loads and the connecting beams exceeds 0.9m depth. Here two
concrete slabs are placed from which one on top of another and connected with
foundation walls in both directions and it forms a cellular raft
foundation.Rigid frame mat is very rigid and is economical when the required
slab thickness is very high.
Written By : Parag Kamlakar Pal
B.E (Civil Engineering), NICMAR (
Advance Construction Management)
Followings are the different types of raft foundation used in construction: