4 Types of shallow foundation most commonly used in Building Construction

Generally shallow foundations are used in construction of building when the hard strata is available on construction site at shallow depth which is always not greater than the width of foundation.

There are 4 types of shallow foundations which are most commonly used while construction of any building having hard strata at low depth.

                1. Spread Footing

                2. Combined Footing

                3. Strap Footing

                4. Raft or Mar Foundation

1. Spread Footing: The spread footings are those which spread the super imposed load of the structure over a large area. The spread footings may be of following types.

        a) Single footing for a column
       
        b) Stepped footing for a column
      
        c) Slope footing for a column
   
        d) Wall footing without steps               and with steps
       
        e) Grillage foundation

Whene heavy structural loads from column are required to be transferred to a soil of low bearing capacity, the most economical foundation is grillage foundation and its depth is limited to 0.9 to 1.6 m.
The base for the first tree types of footings is made up of concrete.

2. Combined footing: In general the combined footing is the common footing which is constructed for two or more columns nearby each other. A combined footing is provided in two shapes generally. One is rectangular and other is trapezoidal. Rectangular footing is provided when each column is loaded equally or iterior column carries greater load. But the trapezoidal footing can be provided under any loading condition.

3. Strap footing: When two or more footings are comnected by means of beam, it is called a strap footing. It is used where distance between two columns is so long that the combined footing can not be provided.

4. Raft or mat foundation: A foundation consisting of a thick reinforced concrete slab over the entire area of bottom of structure, is known as raft foundation or mat foundation. It is used when the allowable soil pressure is low or structural loads are heavy and if the required area of footing is greater than half the total area of the structure, then it is more economical to use raft or mat foundation.