Pile Foundation- Application of Pile Foundation

Pile foundation is categorized under deep foundations which provides more structural safety and stability for the superstructure constructed above. This type of deep foundation is costlier and massive in construction when compared to shallow foundation. The reason for choosing pile foundations when compared with shallow foundations is purely based on certain conditions of the site. These conditions are explained in the coming sections.

Pile Foundation Applications

The basic conditions for which the pile foundation can be applied are, when
  1. The Compressibility of the Soil is Less
  2. The foundation subjected to horizontal force
  3. The presence of expansive or collapsible soils
  4. The action of Uplift forces
  5. The loss of bearing capacity of soil

1. Pile Foundation when the Compressibility of Soil is Less

If the site does not have a sufficient layer of soil to take up the load from the superstructure and transfer it to the soil safely, piles are constructed to transmit the load from buildings to the rock strata underlying the soil. The figure-1(a) shows this. If we did not find rock strata to transfer the load, the soil is used to transmit the load from the structure in a gradual manner. This is shown in figure-2(b).
Fig.1: Pile Foundation For Compressible Soils

2. Pile Foundation to resist the Horizontal Force

The foundation when subjected to a horizontal force will undergo bending. The pile foundation will resist this bending along with the action of bearing the vertical load and properly transmitting to the below surface. Mostly the design and the construction of foundations for tall structures or earth-retaining structures face this issue. These structures are subjected to wind force or earthquake forces in the high extreme.
Fig.2.Pile Foundation Undergoing Bending action

3. The presence of expansive or collapsible soils

Depending on the site, it may have expansive or collapsive soil to a considerable depth. With the variation in moisture content, the expansive soil can either shrink or swell. These hence might have a considerable amount of swelling pressure also. 
Use of shallow foundations in these situations is really uneconomical and unsafe. 

Fig.3: Pile Foundation in Expansive or Collapsive soil

4. Pile Foundation for Uplift Action

When foundations of huge structure extend beyond the water table, it will be subjected to uplift pressure. The pile foundation has good ability to resist these uplift forces.

Fig.4.Pile Foundation Under Uplift Force

5. Pile Foundation to Avoid loss of bearing capacity

The piers and the abutments in bridge construction are made over the pile foundations in order to avoid the loss of bearing capacity due to soil erosion.  This is a common issue for shallow foundations.
Fig.5. Zone of Erosion in the Case of Pile foundations Constructed

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