Foundation and its type

Foundation 

Foundation and its type

Foundation is the lowest part of the structure which provide a base or superstructure in a proper way. The soil which is located immediately below the base of the foundation is called subsoil while the lower portion of the foundation which is direct in contact with the sub soil is called Footing.

 Function of foundation

 The basic function of foundation is to translate the dead load, superimposed load or live load and wind load from a building to the soil on which the building rest in such a way that settlement are permissible limit without considering cracks in superstructure
 soil does not fail when loads are  transmitted to the subsoil.
 It settles if settlement is slight and uniform throughout. No damage will be caused to the building.

 Classification of foundation

 Foundation may be broadly classified under two heads -
1) Shallow Foundation
2) Deep Foundation

 Shallow Foundation 

 If the depth of Foundation is less than its breadth or width then it is called shallow foundation. From the point of view of design, foundation of the following types: -
a) spread footing
b) combined footing
c) strap footing
d) mat or raft footing

 Spread Footing
Spread footing are those which spread the superimpose load of the Wall or column over a larger area

 Combined Footing
 A spread footing which support two a more column is termed as combined footing. The combined footing may be of the following kinds : -
 Rectangular footing
 Trapezoidal footing
Combined footing for column will be  rectangular in shape if they  carry equal loads. The design of rigid rectangular combined footing should be done in such a way that CG of column load coincide with the centroid of the footing area. If the column carry unequal load the footing is of trapezoidal shape.

 Strap Footing
 If independent footing of two columns are collected by Beam then it is called a strap footing. A strap footing may be used where distance between the column is so large.

 Mat Foundation or Raft Foundation
 A combined footing that covers the entire area beneath the structure and support all the walls and columns when the allowable soil pressure is low or the building loads are heavy, the use of spread footing good cover more than one half of the area. carry equal Lords the design of rigid rectangular combined footing should be done in such a way that CG of column load side with the centroid of the footing area if the column carry unequal load the footing is of trapezoidal shape.

Deep Foundation 

 If the depth of the foundation is more than its breadth or width then it is called Deep Foundation.

 Deep Foundation may be of the following types : - 

a) Deep strip,  rectangular and square footing 

b) Pile foundation 

c) Pier foundation 

d) Well foundation

Note - We will discuss deep foundation in our next post.