Correct Answer - Option 4 : mat
Concept:
A raft or mat foundation is a combined footing that covers the entire area beneath a structure and supports all the walls and columns. When the allowable soil pressure is low, or the building loads are heavy, the use of spread footings would cover more than one half of the area and it may prove more economical to use mat or raft foundation.
Piles are vertical columns driven into the ground on which wooden or concrete platforms are supported. The piles are driven at regular distances. The size and distance apart of the piles depend upon the bearing capacity and type of soil and the load of the structure.
Grillage foundation is generally used for heavy structure columns piers and stanchions. It consists of two or more tiers of beams laid at right angles to distribute the load over a large area.
