The type of footing in which the load bearing structures share the common rectangular or trapezoidal footing is called:

 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.