Types of Foundation

Foundation is the lower part of structure which is in direct contact with the ground to which the load s are transmitted while footing is the lowermost portion of foundation which is in direct contact with sub-soil. Following are the main foundation which is generally used for any civil structure as per site condition:-

1.       Shallow Foundation: - If the depth of foundation is less than breadth then it is called shallow foundation. i.e. (D≤W, or,D/W ≤2)

It has following types:-

A.      Spread Foundation:- A footing provided to support individual column is known as spread footing.i.e (L/W =between 1 and 2)

B.      Continuous Foundation:- If the length of footing is more than width of the footing  and chances of differential settlement is less, it is called continuous footing.i.e (L/W >

C.       Strip Foundation:- If the length of the footing is much more than width of the footing, it is called strip footing.i.e. (L>>W)

D.      Combined Footing:- A footing which supports two ore more column is termed as combined footing.The shape of rectangular footing may be  rectangular, square, trapezoidal or triangular. The shape of footing is so proportioned the CG of supporting area is in line with the CG of links.

E.       Strap Footing:- When two or more than two isolated footing are connected by a beam, this is called strap footing and beam connecting the footings is called strap beam.

F.       Mat Foundation:- Mat is combined footing that covers the entire  area beneath a structure and supports all the walls and columns. The mat foundation with extra beam connecting the column is called raft foundation. Normally it is provided under following circumstances :

i.                     on low bearing capacity

ii.                   foundation covers more than 50% area.

iii.                  Heavy load to take safely, etc

G.     Grillage foundation:- It is special types of isolated footing, generally provided for heavily loaded steel stanchions. It consists of one or two tiers of wooden or rolled steel sections with space filled with concrete.

H.     Stepped Footing:- It is provided only when the existing ground is in the form of slop. In case of sloppy ground, 1st  lower footing shall be constructed.

I.         Machine Foundation:- This foundation is used for support of machine. The weight of foundation should be 2.5 to 3.5 times the weight of machine.

2.      Deep foundation: - If the depth D of foundation is greater than breadth W,then it is  called deep foundation. It is provided when load of the super structure is heavy, poor bearing capacity, subsoil, water level high. Fluctuation in subsoil water level and the structure is situated seashore or river bed. It is of following types.

A.     Pile foundation:- (Load is taken by bearing & friction)

i.                    End bearing pile (used to transfer load through water or soft soil to a suitable bearing stratum)

ii.                  Friction  pile (used to transfer

iii.                Compaction pile (Used to compact loose granular soil and thus increasing bearing capacity)

iv.                 Tension pile (To protect the structure through uplift pressure).

v.                   Anchor pile (To provide the anchor against horizontal pool.

vi.                 Feeder or Dolphin pile (Used to protect structure in water against impact caused by ship or other floating objects).

vii.               Better pile (This pile is used to resist inclined force), Ex:- Simplex, Franki, Vibro, Mc-Arthurs, Precast, Sheet pile.

B.      Pier Foundation (Load is taken only by bearing)

i.                    Open cassion: - It is open at top and so well as bottom.

ii.                  Closed cassion:- Where bearing stratum is available at shallow and no chances of erosion below the foundation. It is closed at top and open at bottom. It is also known as floating cassion.

iii.                Pneumatic cassion .

3.      Floating Foundation: - When the pressure exerted by the overburden soil and structure  (including foundation) are equal then the foundation is called floating foundation.