The two main classifications of the foundation are Shallow Foundation and Deep Foundation. Each type is explained briefly. Shallow foundation is foundation system that transmit the loads to the near-surface strata. These foundation units are placed at a shallow depth. If Df is the vertical distance from the ground surface to the bottom of the structural base, then for deep foundation Df/B is greater than 3 to 4. The level at this depth is the foundation level.
- A shallow foundation is the one with the depth to breadth ratio of the foundation, less than 1, i.e (D/B <1).
- This is the first choice for any building construction.
- If the soil within the shallow depth does not have sufficient bearing capacity to take up the load, then we go for a deep foundation.
- The depth of shallow foundation is taken from 60 to 75cm.
- The height of the basement must have a minimum value of 35cm. Generally, 45 cm is used.
Watch Video on Types of Foundation in Construction
The major classification of the shallow foundation are:
- Isolated foundation or Spread foundation
- Wall foundation
- Combined footing
- Continuous foundation
- Cantilever or Strap Footings
- Raft or Mat Foundation
- Grillage foundation
1. Isolated Foundation or Strip Foundation
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Fig.2. Isolated Footing |
- This is the foundation that is made for single columns.
- It is the type of foundation employed for most of the residential construction.
- Isolated footings can be pyramidal, or square or stepped.
Read More on: Isolated Footing and Its Features
2. Wall foundation
Fig.3. Wall Footing Image Credits:Â www.bates.edu |
- These are continuous support or strip form concrete support provided for a continuous wall or a closely spaced column arrangement.
- It is mainly provided as a support for load-bearing walls.
- Used for subsoils with sufficient bearing capacity.
3. Combined Footing
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Fig.4. Combined Footing |
- Combined foundation are foundation made for two adjacent columns.
- If the load on each column is equal, then the foundation takes the shape of a rectangle.
- If the load on each column is different, the foundation takes the shape of a trapezium.
4. Continuous Foundation
- Foundation provided for columns more than two in number are called continuous foundation.
- It is mainly constructed in the perimeter of the building.
5. Cantilever or Strap Footing
Fig.6. Cantilever Footings Image Credits:Â Lecture Note COSC 421 (M.E. Haque) |
- These are combined footing where the footings constructed under the columns are build independently and they are joined using a strap beam.
5. Raft or Mat Foundation
Fig.6. Mat or Raft Foundation Image Credits:Â Lecture Note COSC 421 (M.E. Haque) |
- This is a thick concrete reinforced slab foundation constructed to support the whole area of the building.
- The area can be the same or greater than the building area, depending on the bearing capacity of the soil.
- It is constructed when the soil conditions are poor and we do not wish to go for pile foundation.
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