Raft foundation is a thick concrete slab reinforced with steel which covers the entire contact area of the structure like a thick floor. Sometimes area covered by raft may be greater than the contact area depending on the bearing capacity of the soil underneath. The reinforcing bars runs normal to each other in both top and bottom layers of steel reinforcement.
A foundation is the element of an architectural structure which connects the structure to the ground, and transfers loads from the structure to the ground. Foundations are generally considered either shallow or deep.
Objects of foundation :
To distribute the load of the structure over a larger area of substratum and prevent overloading.
To prevent tilting and over-turning of the structure and increasing its stability.
To prevent the lateral escape of the supporting material.
To provide a leveled base for the super-structure.
To prevent unequal settlement of the soil and super-structure by loading the sub-soil evenly.
- Soil type – especially expansive clay soil
- Poorly compacted fill material
- Slope failure, mass wasting
- Poor construction, and
Types of foundation. Shallow foundations (sometimes called 'spread footings') include pads ('isolated footings'), strip footings and rafts. Deep foundations include piles, pile walls, diaphragm walls and caissons.