Foundation & It’s Types

In engineering, the definition of the foundation is the element of a structure that is directly contacted to the ground and transfers loads from the structure to the ground.

Foundations are divided as shallow and deep foundations.

Types of Foundation:

Following are different types of foundations:

  1. Shallow foundation

    • Isolated footing
    • Combined footing
    • Strip foundation
    • Raft or mat foundation
  2. Deep Foundation

    • Pile foundation
    • Drilled Shafts Foundation

    # Types of Shallow Foundation

    1.  Isolated Footing:

    An isolated footing is the most commonly used type of foundation used in building construction. This foundation is built for a single column and is also called the pad foundation.

The shape of an isolated footing is square or rectangle. It is used when loads from the structure are taken by the columns. Size is calculated depending on the load on the column and the load-bearing capacity of the soil.
The rectangular isolated footing is chosen when the foundation faces moments due to the eccentricity of loads or due to horizontal forces.   

2. Combined Footing

A combined footing is built, when two or more columns are near to each other and their isolated footings meet each other. It is a mixture of isolated footings, but their structural design different.
The shape of the combined footing is rectangle and is used when loads from the structure are taken by the columns.

3. Spread footings or Strip footings:

Spread footings are those footing whose base is farther than load-bearing wall foundations. The farther base of spread or strip footing type spreads the weight from the building structure over huge areas and provides good stability.
Spread footings are used for single columns, walls and bridge piers where the load-bearing soil layer is within 3m or10 ft from the ground surface. Soil bearing capacity must be more sufficient to support the weight of the structure over a huge base area of the structure.
These footings should not be constructed on soils where there is a high possibility of a ground flow of water above bearing layer of soil which may lead to a collision, scour or liquefaction.

 

4. Raft or Mat Foundation:

Raft foundation is those types of foundation which are spread across the whole area of the building to support heavy loads from columns and walls. The mat foundation is used for columns and walls foundations where the loads from the structure are very high. This is used to save the differential settlement of single footings, thus designed as a single mat or combined footing of all load-bearing elements.  
Raft foundations should not be constructed where the groundwater table is above the bearing surface of the soil. The use of foundation in such conditions may result to scour, collision and liquefaction.

#Types of Deep Foundation

 

1. Pile Foundations

Pile foundation is a type of deep foundation which is constructed to transfer heavy loads from the structure to hard soil strata much below the ground level.
Pile foundations are constructed to transfer heavy loads of structures by means of columns to hard soil strata which is much deep below the ground level where shallow foundations cannot be used. This is also constructed to prevent uplift of a structure due to lateral loads (earthquake and wind forces). 

2. Drilled Shafts Foundation:

Drilled shafts, also called a caisson foundation. It is a type of deep foundation and has action same to pile foundations explained above in pile foundation, but are more capacity cast-in-situ foundations. It withstands loads from structure through shaft resistance, toe resistance or combination of both of them. The construction of drilled shafts is done by using an auger.

 

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