TYPES OF FOUNDATIONS

The foundations are the sub structure of the building which transmits the load to the soil. The foundations may be broadly classified as shallow foundation and deep foundation

1. Shallow foundation : 
A foundation is said to be shallow if its depth is equal to or less than its width.

2. Deep foundation :
A foundation is said to be deep if its depth is equal to or greater than its width. 

TYPES OF SHALLOW FOUNDATIONS

1. Spread footing
Categories of isolated foundation footings - TheCivilEngineer.org
The spread footings are those which spread the super-imposed load of the structure over a large area. The spread footing may be classified as below
  • Single footing for a column
  • stepped footing for a column
  • sloped footing for a column
  • wall footing with and without steps
2. Grillage footing

The base of the first three type of footings is made of concrete When heavy structural loads from column are required to be transferred to the soil of low bearing capacity, the most economical foundation is grillage footing. The depth of grillage footing is limited to 0.9 to 1.6 m.

3. Combined footing

The common footing which is constructed for a two or more columns, is called combined footing.The general shape of combined footing is either rectangular or trapezoidal. A combined rectangular footing is designed where the loading condition of two column are of the same load or internal columns carries greater load. A trapezoidal combined footing is provided under any loading conditions.

4. Strap footing

when two or more footings are connected by the beam, It is called strap footing. It my be used where the distance between the columns are so great and combined trapezoidal footing becomes a quite narrow, with high bending moments.

5. Raft or mat footing


A foundation which covers the thick reinforced concrete slab on the entire area of the bottom of the structure, it is known as the raft or mat foundation. When the allowable soil pressures are low and building loads are heavy and if the required area of footing is more than half of the total area of the structure, then it is more economical to use raft or mat foundations.

6. Eccentric footing 

Important Points to Remember for Eccentric Footing, Cantilever ...
The Eccentric footing is a one sided footing. Where a building is surrounded by a existing structures which are more deep than our structure, There we have to design eccentric footings. 
The Eccentric Footings are so designed and proportioned that the C.G. of the superimposed load coincides with the C.G. of the base area, so that the footing is subjected to concentric loading, resulting in uniform bearing pressure.

TYPES OF DEEP FOUNDATIONS

1. Pile foundation 

A pile is a long vertical load transferring member composed of either timber, steel or concrete. In pile foundations, a number of piles are driven in tn the base of the structure. The pile foundation is generally used when the soil is compressible, water logged and made-up type. It is most suitable for bridges.

2. Pier foundation


In pier foundation, hollow vertical shafts are sunk upto the hard bed and hollow portions are then filled up with inert material such as sand or lean concrete. The pier foundations are generally suitable for heavy structures such as flyovers on sandy soil or soft soil overlying hard bed at reasonable depth. 

3. Cassion or well foundation


The open cassion is a box of timber, metal, reinforced concrete or masonry which is open both at the top and the bottom and is used for building and bridge foundations. This type of foundations are most commonly used for bridges in india.

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