Using the Raft Foundation and Its Types in Construction

The raft foundation which is also known as Mat foundation is used in type of foundation system very commonly. The working principle of raft foundation discusses about choose raft, types of raft foundation, materials of raft foundation, raft construction steps etc.

Definition the Raft Foundation

Raft foundation is actually a substantial solid slab quiescent on a large area of soil reinforced with steel, supporting columns or walls and transfer loads from the structure to the soil. Usually, mat foundation is stretch over the entire area of the construction it is supporting.

Raft foundation of structures like residential or commercial buildings are supported where soil situation is poor, storage tanks, silos, foundations for heavy industrial equipment etc.

You have to understand important idea about when to use raft foundation.

How Raft Foundation Works

Raft foundation transmits the whole load from the building to the entire ground floor area. Stress distribution mechanism of raft foundation is not very hard. Whole weight of the structure and self-weight of the mat is calculated and is divided by the whole area of the foundation that is covering to calculate the pressure on the soil.

The contact area of raft foundation of with soil is much more than any other type of foundation, large area of the load distribute and thus the soil stress is lesser and shear failure of soil is also possible to be reduced.

Choosing Raft Foundation Effectively

One of the most vital aspects is choosing the right type of foundation is important for foundation design. There is some scenario where raft foundation can happened.

Those are listed below:

1. The bearing capacity of the soil has to be low.
2. Large area is needed to distribute the load of the structure.
3. The total ground area beneath the structure has to cover approximately cover 50% for any foundation area.
4. The columns or walls are closely placed for the individual footings can overlap.
5. Reducing soil stress is must need.
6. There is a possibility of differential settlement in case individual footing is used.
7. When soil strata are unpredictable and contain pockets of compressible soil.
8. Basement has to be build.

Different Types of Raft Foundation

There are different types of Raft foundation is used depending on the soil condition and the imposed load on the foundation. The different types of raft foundation which is used in construction are as follows:

(A) Flat plate Mat
(B) Plate Thickened under Columns
(C) Two way Beam and slab
(D) Plates with Pedestals
(E) Piled Raft
(F) Cellular Raft Foundation

Raft Foundation?s Construction Process

Various steps of Raft foundation construction are noted below:

1. Desired depth has to be identified for the foundation which is to be provided.
2. The required depth of the soil has to be dug out.
3. Soil compactness
4. Waterproofing membrane has to be provided
5. Plane cement sand paste poured in 3?.
6. The required spacing maintain for lay reinforcement has to be used by Spacer
7. Curing
8. Pouring the concrete to the desired depth

Construction Material for Raft Foundation

(A) Formwork
(B) Spacer
(C) Reinforcement
(D) Concrete


Raft foundation is very popular and very common type of foundation system. This construction process is simple and very effective in shallow depth where the condition of the soil is very poor.

Anyone who wants to build safe construction has to analyze the condition of both loading and soil for an optimum use of the foundation.

Using the Raft Foundation and Its Types in Construction