Any building structure consists of two main structural parts. One is the sub-structure and the other is the superstructure. The superstructure is the structural component constructed above the ground and the sub-structure is the structural components constructed below the ground.
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If so, the sub-structure plays the objective of transferring the load coming from the superstructure to be uniformly distributed on the ground below without any differential settlement. Foundation is the sub-structure component of any building construction that transfers the loads coming from the superstructure to the below soil in a uniform and safe manner.

Purpose of a Foundation in Construction

The main three objective or purpose of foundation in constructing any structure are:

  1. To distribute the load coming from the superstructure to the soil uniformly
  2. To provide a level surface in order to construct the above masonry or concrete structure.
  3. To prevent penetration of the moisture to the superstructure thus preventing the chances of cracks.

  1. The bottom portion of the foundation is called as the footing.
  2. The component between the sub-structure and the super-structure is called as a plinth.

Important Foundation Design Features

Main parameters that are studied in the design of the foundation for any structure are:

  1. Bearing Capacity of Soil
  2. Safe Bearing Capacity of Soil
  3. Ultimate Bearing Capacity of Soil
  4. Allowable Bearing Capacity of Soil
  5. Factor of Safety
  6. Settlement of Foundation
We will discuss the above-mentioned parameters in simple form.

  • The supporting power of the given soil is called the bearing capacity of the soil. This tells how strong the soil is in order to support a given load.
  • Safe Bearing capacity is the load that can be applied tot he soil so that it does not undergo any shear failure. ( Differential settlement is irrespective).
  • Ultimate Bearing capacity is defined as the load at which the soil loses its resistance to the applied load. It is the maximum load a given soil can take
  • Allowable Bearing pressure is defined as the load at which the soil neither fails under sear nor settlement.
  • The factor of safety is defined as the ratio of ultimate bearing capacity to the safe bearing capacity of the soil.
  • Settlement of foundation is an issue when it is a differential settlement. The maximum differential settlement for sandy soil must not be greater than 25 mm and for clayey soil,it must not be greater than 40mm.