1. Civil Engineering Department
Types of foundation
Prepared by :
Prof. Alka M. Shah
Civil Engineering Department
Nirma University

2. What is Foundation ?
Lowest part of a structure directly in contact with the ground and transmits all the loads to the sub-soil below it.
Majority of structure fails due to failure of their foundation
PURPOSE
To support structure
Distributes the loads over a larger area
Minimizes the differential settlements
Increases stability & prevents overturning
Distribute non-uniform load uniformly to the soil

3. Foundation and Footing are same?
Foundation: Part of the structure which is in direct contact with the ground to which the loads are transmitted.
Footing: Lower most portion of foundation which is in direct contact with the sub soil is called footing.

4. DEEP FOUNDATIONS D > B
Types of Foundation
FOUNDATIONS
SHALLOW FOUNDATION
D ≤ B
DEEP FOUNDATIONS D > B

5. Suitability of FOUNDATION
SHALLOW FOUNDATION
Bearing capacity of soil is more.
ground water table(W.T) is low.
dewatering of foundation is not required.
top layers of soil are uniform and stable.
Load on the structure is less.
Deep FOUNDATION
Bearing capacity of soil is low.
ground water table(W.T) is high.
dewatering of foundation is costly and difficult.
top layers of soil are non uniform and unstable.
Load on the structure is more.

6. TYPES OF SHALLOW FOUNDATION
1) SPREAD FOOTING
i) Continuous footing (strip or wall)
ii) Isolated column footing a) Square
b) Circular
c) Rectangular
iii) Inverted arch footing
iv) Reinforced concrete footings
2) STRAP FOOTING
3) COMBINED FOOTING
i) Rectangular
ii) Trapezoidal
4) RAFT FOUNDATION
5) GRILLAGE FOUNDATION

7. 1) SPREAD FOOTING
Carries a single column
Used to spread out loads from walls of columns over a wider
area
Consists of concrete slabs located under each structural
column and a continuous slab under load-bearing walls.
Commonly used due to their low cost & ease of
construction.
Used in small to medium size structures with moderate to
good soil condition.
For high rise buildings it is not efficient.

8. Simple wall footing without masonry offsets (SBC is high)
Wall footing with masonry offsets (Stepped wall footing)
(SBC is low)

10. STRIP/WALL FOOTING
A spread footing for a continuous wall is called strip footing. (Used to support load bearing walls)

11. Inverted Arch footing
Used on soft soils to reduce depth of foundation.
End columns must be strong to resist outward pressure caused by arch action.

12. Reinforced Concrete footing
Used where the walls are subjected to heavy loads & soil bearing capacity is low

13. ISOLATED COLUMN FOOTING
Used to support individual columns.

15. 2) COMBINED FOOTING Supports two columns
the two columns are so close to each other that their individual footings would overlap
one column is placed right at the property line
C.G. of column load and centroid of the footing should coincide

16. COMBINED FOOTING
Rectangular footing
Trapezoidal footing

17. A combined footing will deform as shown in fig below
The eccentric loading condition upon the left end, due to the restrictions of a property line, will generate tensile stresses on the top of the footing.

18. 3) CANTILEVER/STRAP FOOTING
Two isolated footings connected with a strap or beam
Connects in such a way that they behave as one unit
The strap acts as a connecting beam and does not take any soil reaction. The strap is designed as rigid beam.
It does not provide bearing

19. to connect an eccentrically loaded column footing to an interior column.
Used to transmit the moment caused from an eccentricity to the interior
Can be used instead of combined footing if the distance between two columns is large
More economical than combined footings

20. 4) RAFT FOUNDATION
Large reinforced concrete slab supporting no. of columns & walls
area of spread footings or combined footings exceeds about 50 percent of the gross area of the building
Greater weight & continuity of a mat provides sufficient resistance

21. RAFT / MAT FOUNDATION

22. RAFT / MAT FOUNDATION

23. Raft/Mat Foundation is suitable under following conditions
Structural loads are heavy or the soil condition is poor
Soft or loose soils having less bearing capacity
Foundation soil is non-homogeneous and prone to excessive differential settlements
Lateral loads are non-uniform
Columns are so close that their individual footings would overlap
To resist water pressures when groundwater extends above the floor level of the lowest basement of a building
There is a large variation in the loads on individual columns

24. 5) GRILLAGE FOUNDATION Types of Grillage foundation
Used to transmit heavy loads from steel columns to a soil having low bearing capacity
Avoids deep excavation
Reduces pressure intensity
Lighter & economical
Used in masonry bridge seat, bus stands, railways etc
Made up of a rolled steel joints (RSJ) known as grillage beams
Types of Grillage foundation
Steel grillage foundation
Timber grillage foundation

25. A type of foundation often used at the base of a column
A type of foundation often used at the base of a column. It consists of one, two or more tiers of steel beams superimposed on a layer of concrete, adjacent tiers being placed at right angles to each other, while all tiers are encased in concrete.
This is dependable foundation and is used in those place where the load of the structure is pretty and bearing capacity of soil comparatively poor
The grillage foundation helps in distributing the load over a wider area of subsoil.
The grillage foundation helps in avoiding deep excavations as the necessary base area is provided for the load of transmission
This type of foundation generally used for heavy structure columns piers and steel stanchions etc.

26. GRILLAGE FOUNDATION

27. Steel Grillage foundation
Consists of rolled steel joists in single or double tiers

29. Timber Grillage foundation
Uses timber planks & timber beams
No concrete is embedded between the timber joists
Used in waterlogged areas

30. Grillage foundation for Wooden/Timber Post

31. SHALLOW FOUNDATION Advantages: Cost (affordable)
Construction Procedure (simple)
Material (mostly concrete)
Labour (doesn’t need expertise)
Disadvantages:
Settlement
Foundation gets subjected to pullout, torsion etc
Irregular ground surface(slope, retaining wall)

32. TYPES OF DEEP FOUNDATION
PILE FOUNDATION
2) CAISSONS OR WELL FOUNDATION
3) COFFER DAMS

33. 1) Pile foundation
Pile: Column-like foundations going deep into the subsoil.
Piles are structural members that are made of steel, concrete or timber.
Preferred:
i)When soil bearing capacity is poor.
ii) Non availability of proper bearing strata at shallow depth.
iii) pumping of sub soil water would be too costly.
iv)Heavy loads from super structure for which shallow foundation will be uneconomical.

34. 1) Pile foundation
Classification of pile foundation
Based on function:
-End bearing: Transfer load to through soil or water…
-Friction: Transfer load by means of skin friction…
-Compaction: Compacting loose granular material and thus increasing SBC…
-Tension(uplift): Anchor down the structures subjected to uplift due to hydraulic pressure or due to overturning…

35. Classification of pile foundation
-Anchor: Provide anchorage against horizontal pull…
-Fender and dolphins: Protect against impact from ships.
-Sheet: To reduce seepage and uplift under hydraulic structures like dams…

41. Under reamed piles
Under reamed piles are bored cast-in-situ concrete piles having one or more number of bulbs formed by enlarging the pile stem.
These piles are best suited in soils where considerable ground movements occur due to seasonal variations, filled up grounds or in soft soil strata.
Provision of under reamed bulbs has the advantage of increasing the bearing and uplift capacities. It also provides better anchorage at greater depths.
These piles are efficiently used in machine foundations, over bridges, electrical transmission tower foundation sand water tanks

43. Caissons
The word caissons derived from the French word caisse meaning a box
Box like structure, round or rectangular which sunk from the surface of either land or water to some desired depth
Used for placing foundation under water

44. Types of Caissons Pneumatic caisson (closed at top and open at bottom)
Box caisson
(open at top and closed at bottom)
Open caisson or wells
(open at top and bottom)
Single, Multiple and Cylinder

45. Box caissons Strong water tight vessel
Built on land and floated up to site and then sink in to the water
Used when loads are not heavy
Bearing stratum is available at shallow depth
Water depth is 6 to 8 m
Foundation bed not required
Material is loose

47. Open or Well caissons ( Well Foundation)
Used for buildings and bridge where soil liable to scour
No firm bed is available

48. Pneumatic caissons It is useful when well foundation is not possible
Depth of water 12 to 35 m

49. Cofferdams
Cofferdam is a temporary structure which is built in a river, lake or dam to remove water from the area and make possible to construct
Require in dams, docks and bridge pier

50. Types of Cofferdams
1. Earth fill cofferdam

51. 2. Rock fill cofferdam

52. 3. Rock fill crib cofferdam

53. 4. Single wall cofferdam

54. 5. Double wall cofferdam

55. Circular cellular cofferdam
Mostly used for de-watering areas in places where depth of water is from 18 to 21 m
Two types 1. Diaphragm cellular cofferdam
2. Circular cellular cofferdam
Circular cellular cofferdam

56. Diaphragm cellular cofferdam

57. Difference between caisson and cofferdam
Permanent structure used
for placing foundation in
correct position
It is build on dry bed,
floated to the desired site
and sunk to desired depth
Preferred when work area
is small and water depth
is more
Used where driving of
sheet pile is impossible
COFFERDAM
Temporary structure used
for construction work under
reasonably dry condition and
demolished after completion of
work
It is build in river or lake
Preferred when work area is
large and water depth is small
Used where driving of sheet
pile is easily possible

58. FOUNDATION IN BLACK COTTON SOIL
Black cotton soil is very dangerous to place foundation and bearing capacity
is about 50 to 100 kn/m2
Variation in the volume change of soil extent from 20 to 30 % of original
volume
Alternate swelling and shrinkage results in formation of cracks which are of
15 to 20 cm wide and 2.5 to 4 m deep

60. Foundation in black cotton soil
Types of Foundation in black cotton soil
Strip (wall) or pad (column) foundation
Suitable when load is medium and swelling pressure is little
Foundation in black cotton soil

61. Foundation in black cotton soil
Suitable when swelling pressure is high and having high shrinkage
properties
Used at place where high rainfall
Foundation in black cotton soil

62. 2. Pier Foundation
Suitable foe wall carrying higher load
Gap between arch and ground would permit free vertical movement of soil during swelling and shrinkage

63. Precaution For The Safety of Foundation In Black Cotton Soil
For heavy structure raft or pile foundation is preferable
If possible remove black cotton soil
Construction work should be carried out in dry season
Black cotton soil not allowed to come in direct contact with the foundation
R.C.C. bands 10 to 15 cm deep should placed at plinth, lintel level
Gap on either side of foundation should filled with sand
Below foundation, 30 cm thick layer of moorum must provided

64. Factors Affecting Foundation Selection
PRIMARY FACTORS AFFECTING FOUNDATION CHOICE:
Sub-surface soil
Ground water table conditions
Type of structure
Magnitude of load
SECONDARY FACTORS AFFECTING FOUNDATION CHOICE:
Construction access, methods and site conditions
Environmental factors
Building Codes and Regulations
Impact on surrounding structures
Construction schedule
Construction risks

65. Ground water table conditions
Presence of groundwater near a footing is undesirable because:
Footing construction below GWT is difficult and expensive,
Groundwater around a footing can reduce the strength of soils,
It may also cause hydrostatic uplift,
Frost action may increase,
Waterproofing problems.
If Ground water table is high, raft or grillage foundation is desirable.
If ground water table is low or at a high depth from foundation than column foundation is desirable.

66. Subsurface condition and Building structural requirements

67. THANK YOU