What is Foundation? Types and Classification of Foundation…..
What is Foundation?
A building has 2 main components:-
(a) Foundation or Sub-structure:- It is the lowest part of the building or any structure which transmits the load to the soil.
(b) Super Structure:- It is that part of the structure which is above ground level.
Types of Foundations:- Foundations are broadly classified as:-
- Shallow Foundation:- When the depth is equal to or less than its width, then it is said to be a shallow foundation.
- Deep Foundation:- When the depth is equal to or greater than its width, then it is said to a deep foundation.
Types of Shallow Foundations:- Shallow foundations are of the following types:
(a) Spread Footing:- Spread footings are the footings that spread the superimposed load of the structure over a large area.
Spread footings are of the following types:
- Sloped footing for a column
- Stepped footing for a column
- Single footing for a column
- Wall footing with or without steps
- Grillage foundation
When heavy structural loads of columns are required to transfer to the soil of low bearing capacity then the Grillage foundation is the most economical foundation, in which the depth is limited to 0.9m to 1.6 m. The base of Sloped, Stepped & Single footing is made of concrete.
(b) Mat or Raft Foundation:- Mat or raft foundation is the foundation in which a thick reinforced concrete slab covering the entire area of the bottom of the structure. If the required area of footing is more than half of the total area of the structure and when the building loads are heavy or the allowable soil is low, then mat or raft foundation is more economical.
(c) Combined Footing:- It is the most common footing which is constructed for two or more columns. The general shape of combined footing is rectangular or trapezoidal. We provide combined rectangular footing where the loading condition is either of the two columns are equally loaded or the interior column carries a greater load. And in the case of trapezoidal combined footing, we can provide it under any condition of loading.
(d) Strap Footing:- Strap footing is the footing when two or more footings are connected by a beam. It is used where the distance between the columns is so great that combined trapezoidal footing will be quite narrow with high bending moments.
Types of Deep Foundations:- Deep foundations are of the following types:
(a) Pier Foundation
(b) Pile Foundation
(c) Well, or Caisson Foundation
Pier Foundation →
Pier Foundation is suitable for a heavy structure such as flyovers in soft soil or sandy soil overlying hard beds at reasonable depth. In this foundation, hollow vertical shafts are sunk up to the hard bed and hollow portions are filled up with inert material such as lean concrete or sand.
Pile Foundation →
Pile Foundation is more commonly used in construction. This foundation is generally used when the soil is water-logged, compressible, and made-up type. In Pile Foundation, a pile is a long vertical load transferring member composed of timber, steel, or concrete. Pile foundation is most suitable for bridges.
Well, or Caisson Foundation →
Well, or Caisson foundation is the most common type of deep foundation for bridges in India. The open Caisson is a box of metal, timber, reinforced concrete, or masonry which is open both at the bottom and the top and is used for both bridges and building foundations.
Classification of Piles:- The Piles are classified as follows:
(a) Classification based on Function:
- Friction Piles
- Sheet Piles
- Bearing Piles
- Batter Piles
- Fender Piles
- Compaction Piles
(b) Classification based on Composition and Materials:
- Timber Piles
- Screw Piles
- Concrete Piles
- Disc Piles
- Steel Piles
- Composite Piles