1. Shallow foundation
NIDA FATIMA ANSARI
B.ARCH III YEAR
2. A foundation is the lowest and supporting layer of a structure and a building component which
transfers building loads to the soil.
There are two basic types of foundations:
SHALLOW - Shallow foundations transfer the load to soil at
the base of the substructure
DEEP - Deep foundations transfer loads far below the
substructure. These foundations penetrate incompetent soil until a
satisfactory bearing stratum is reached.
The objective of shallow foundation is to distribute the structural concentrated load over a
wide horizontal area at a little depth rather than a range of the depths.
Shallow foundation is often selected when the soil has good bearing capacity and the
structural load will not cause excessive settlement of the underlying soil layers.
shallow foundations are more simple and cost effective to construct than deep foundations
because little soil is removed or disturbed.
This foundation is usually utilized in residential and light commercial buildings.
Shallow foundations are generally constructed using in-situ concrete but some substructure
elements can alternatively be constructed in precast concrete in part or whole to improve
speed of construction on site.
4. TYPES OF FOUNDATION
Shallow Foundation System
Mat / Raft Foundation
5. ISOLATED FOOTING
It’s an enlargement at the bottom of a column/ bearing wall that spreads the applied
structural loads over a sufficiently large soil area.
Each column & each bearing wall has its own Isolated footing, so each structure may
include dozens of individual footings.
6. EXAMPLES FOR ISOLATED FOOTING
FOOTING FOR WALL.
FOOTING FOR COLUMN
The foundation consists of concrete slabs located under each structural column and
a continuous slab under load-bearing walls.
For the isolated foundation system the structural load is literally spread out over a
broad area under the building
Most common type of foundation used due to their low cost & ease of construction.
Most often used in small to medium size structure with moderate to good soil
isolated footings may be built in different
shapes & sizes to accommodate individual
needs such as the following:
a) Square Spread Footings / Square Footings
b) Rectangular Spread Footings
c) Circular Spread Footings
d) Continuous Spread Footings
8. a) Square Spread Footings / Pad Foundation
- support a single centrally located column
- the reinforcement in both axes are to
resist/carry tension loads.
b) Rectangular Spread Footings
- Useful when obstructions prevent
construction of a square footing with a
sufficiently large base area and when
large moment loads are present
9. Square spread footing
10. 6 March 2014
11. c) Circular Spread Footings
- are round in plan view
- most frequently used as foundation for
light standards, flagpoles and power
12. Combined footing
This type of footing is adopted when the space between two columns is so small that the
foundation for individual columns will overlap.
Combined footings are proportioned in such a way that the centre of gravity of the loads
coincides with the center of gravity of the foundation. Hence these footings have either a
trapezoidal or a rectangular shape.
13. Cantilever or Strap Footings.
A strap footing is used to connect an eccentrically loaded column footing to an
• The strap is used to transmit the moment caused from an eccentricity to the interior
column footing so that a uniform soil pressure is generated beneath both footings.
• The strap footing may be used instead of a rectangular or trapezoidal combined
footing if the distance between columns is large and / or the allowable soil pressure
is relatively large so that the additional footing area is not needed.
14. MAT FOUNDATION
FOR VERY LOW BEARING CAPACITY OF SOIL, THE STRIP OR ISOLATED FOOTING
MERGE RESULTING IN THE MAT FOUNDATION .
IT IS A SINGLE LARGE CONTINUOUS FOOTING SUPPORTING THE ENTIRE
IT ALSO REDUCES THE DIFFERENTIAL SETTLEMENT BETWEEN THE COLUMNS.
BEAM AND SLAB SYSTEM AMD PLATE
PLATE THICKENED UNDER COLUMN AND FLAT PLATE
15. Mat-slab foundations
16. Mat Foundation often considered to be used when dealing with the following
The structural loads are so high or the soil condition so poor that spread footings
would be exceptionally large
The lateral loads are not uniformly distributed through the structure and thus may
cause differential horizontal movements in spread footings and pile caps.
The continuity of a mat will resist such movement.
The uplift loads are larger than spread footings can accommodate. The greater weight
and continuity of a mat may provide sufficient resistance.
The bottom of the structure is located below the groundwater table, so waterproofing
is an important concern. Because mats are monolithic, they are much easier to
waterproof. The weight of the mat also helps resist hydrostatic uplift forces from the
17. In ground reinforced concrete foundation in cyclonic
area, Northern Australia.
18. ADVANTAGES OF USING SHALLOW
1- Cost (affordable)
2- Construction Procedure (simple)
3- Materials (mostly concrete)
4- Labor (does not need expertise)
DISADVANTAGES OF USING SHALLOW
2- Limit Capacity * Soil * Structure
3- Irregular ground surface (slope, retaining wall)
4- Foundation subjected to pullout, torsion, moment.