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.
