7 Types of Shallow Foundations in Building Construction

The two main classifications of the foundation are Shallow Foundation and Deep Foundation. Each type is explained briefly. Shallow foundation are foundation systems that transmits 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 shallow foundation Df/B is greater than 3 to 4. The level at this depth is foundation level.



Types of Shallow Foundation

  1. A shallow foundation is the one with the depth to breadth ratio of the foundation, less than 1, i.e  (D/B <1).
  2. This is the first choice for any building construction.
  3. 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.
  4. The depth of shallow foundation is taken from 60 to 75cm.
  5. The height of the basement must have a minimum value of 35cm. Generally, 45 cm is used.

Classification of Shallow Foundation

The major classification of the shallow foundation are:
  1. Isolated foundation or Spread foundation
  2. Wall  foundation
  3. Combined footing
  4. Continuous foundation
  5. Cantilever or Strap Footings
  6. Raft or Mat Foundation
  7. Grillage foundation

1. Isolated Foundation or Strip Foundation

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.

2. Wall  foundation

Fig.3. Wall Footing
Image Credits: 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

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: 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: 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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