Foundation/Footing and Its Types (Shallow)

A building is divided into two parts;

i.   Sub-structure (portion below the Plinth level)
ii. Super-structure (portion above the Plinth level)

 Foundation is the lowest part of the structure below plinth level, which provides base for super structure. It does not take up the load of the structure by itself, it only transfers superimposed load to the soil below.

Objective of foundation

•  To provide a leveled base for the superstructure
•  To transmit all superimposed loads of the structure to the soil
•  To increase stability; prevent tilting or overturning of the structure
•  To prevent unequal settlement 

Types of Foundation 

A) Shallow foundation             B) Deep foundation

A) Shallow Foundation (Wide foundation)

 It is placed immediately beneath the lowest part of the super structure. It is spread more horizontal than vertical. The depth is less than or equal to its width. It transfers the loads to subsoil at a shallow depth, close to the ground level.

Types:
1. Spread Footing: 

The base is made wider than the top so as to distribute the load from the superstructure over a large area.

a) Wall (Strip) Footing

 It is generally used for ordinary building with load bearing walls. The successive increment in the width is achieved by providing 5 cm (1/2 brick) offset at both sides.

b) Reinforced Concrete Footing

 In case of heavy loading, R.C.C. footing proves to be economical over brick footing.

c) Inverted Arch Footing

 It is used where the bearing capacity of the soil is very poor and load of the structure is concentrated over the columns.

d) Column Footing

 It is also known as independent/ isolated footing. It may be constructed using bricks, R.C.C. or stones.

2. Grillage Foundation 

 It is used where the load of the structure is excessive and the bearing capacity of the soil is poor. It is recommended where deep foundation is not possible. Steel and timber grillage foundation are generally used.

3. Combined Footings

 In this footing two or more columns are supported by a single base. They can be Rectangular or Trapezoidal in shape.

4. Raft or Mat Foundation

 Generally this type of foundation is used where the load of the structure is excessive and the bearing capacity of the soil is poor or where basement space is desired and pile is very expensive.