1. FOUNDATION Engineering Design of shallow foundation
Prepared by :
Prof. Alka M. Shah
Civil Engineering Department
Institute of Technology
Nirma University

2. What is Foundation ? PURPOSE
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
Major purpose is to transmission of load in such a way soil is not over-stressed and does not undergo deformation
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. DEEP FOUNDATIONS D > B
Types of Foundation
FOUNDATIONS
SHALLOW FOUNDATION
D ≤ B
DEEP FOUNDATIONS D > B

4. 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.

5. 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)

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) Reinforced concrete footings
2) STRAP FOOTING
3) COMBINED FOOTING
i) Rectangular
ii) Trapezoidal
4) RAFT 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)

9. Wall footing
A spread footing for a continuous wall is called strip footing. (Used to support load bearing walls)

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

11. ISOLATED COLUMN FOOTING
Used to support individual columns.

12. ISOLATED COLUMN FOOTING

13. 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

14. COMBINED FOOTING
Rectangular footing
Trapezoidal footing

15. 3) 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

16. 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

17. 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

18. RAFT / MAT FOUNDATION

19. 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

20. Factors Affecting Foundation Selection
FACTORS AFFECTING FOUNDATION CHOICE:
Sub-surface soil
Ground water table conditions
Type of structure
Magnitude of load
Tolerances of structure i.e. permissible values of settlement and tilt etc.

23. PERMISSIBLE DIFPERENTUL SRTTLEMENTS AND TILT IS:1904

24. Basic requirement of foundation
Foundation must be properly located considering any future influence which could adversely affect its performance
Soil supporting must be safe against shear failure
Foundation must not settle or deflect
Should safe against sliding and overturning

25. Design of foundation include
Soil Design
Structural Design

26. Geotechnical Shallow Foundation Design
Soil Design of foundation Include:
Loads coming on foundation W (DL, LL, etc.)
Determination of Allowable Bearing pressure of soil, qa
Determination of area of foundation
Area = [W + Self weight of foundation(10% of W)] / qa
Layout of foundation: such a way that C.G. of foundation coincides with C.G. of load
Upward soil pressure on footing p = W/A < A. B. P

27. THANK YOU