Raft foundation constitutes a thick concrete slab that rests on a large soil area. This foundation supports columns and walls and functions by transferring the loads from the structure to the soil.This foundation is spread over a large area and as such nullifies any differential settlement
This footing is particularly used when the soil has a low bearing capacity and when the chances of differential soil settlement are high
Working Principle of Raft Foundation
In the raft foundation, the load is transmitted from the building to the ground by means of the raft
Its stress distribution mechanism is simple and uncomplicated. For computing the stress on the soil, the total weight of the structure and self-weight of the mat is calculated and divided by the total area of the foundation covered
In raft foundation, the contact area of the foundation with soil is significantly large as compared to other types of foundations. The load is distributed over a larger area, and thus the total stress exerted on the soil is lesser, thereby reducing the possibility of shear failure of the soil
Types of Raft Foundations
Different types of Raft foundations may be employed depending on the condition of the soil and the load imposed on the foundation.
The followings are the different types of raft foundations used in construction
Flate plate mat
The plate thickened under column
Two-way beam and slab Raft
Plate raft with pedestals
Piled raft
Rigid Frame Mat or Cellular Raft Foundation