Question

Match the conditions under which the given type of footing is used:

a. Combined footing	I. For two or more columns
b. Mat foundation	II. For isolated or group of  columns
c. Pile foundation	III. For individual column
d. Isolated footing	IV. For supporting all  columns of structure

1. a – II, b - III, c - IV, d - I
2. a - I, b - IV, c - II, d - III
3. a - II, b - I, c - III, d - IV
4. a - II, b - IV, c - I, d - III

Answer 1

Correct Answer - Option 2 : a - I, b - IV, c - II, d - III

Explanation:

Types of footings and their characteristics:

Types of footings	Characteristics
a. Combined footing	I. For two or more columns If the loads are equal then it is constructed in a rectangular shape. For unequal loading its constructed in a trapezoidal shape.
b. Mat foundation	II. For supporting all  columns of the structure. When the allowable bearing pressure is very low, then this is adopted. Raft is also used to reduce settlement is highly compressible soil by making the wt. of the structure and raft approximately equal to the soil excavated.
c. Pile foundation	III. For isolated or group of  columns. When the strength of the soil layer is very low or less and the incoming load is very high then pile foundation is adopted. It goes deep into the ground and transfers the load to strong solid strata. It is also used to increase the load-bearing capacity of soil by installing a group of piles.
d. Isolated footing	IV. For individual column. It is constructed right below a column and above a strong soil layer and dissipates the load to the much larger area beneath it.

• Strip footing: Strap footing consists of spread footings of two or more columns connected by a beam.

 
It is used where the distance between the columns is sp great that the combined or trapezoidal footing becomes quite narrow. 

• Maximum settlement under raft foundation on clay soil = 65 to 100 mm
• Maximum settlement under raft foundation on sandy soil = 40 to 65 mm
• Maximum differential settlement of foundation in clayey soil = 40 mm
• Maximum differential settlement of foundation in sandy soil = 25 mm