Shallow Foundation Failure

Shallow foundation failure due to the failure of the soil has discussed in this article. In addition to the soil failure, the foundation could fail due to the failure in a structural capacity.

In this article were are discussing the foundation that applied a vertical load.

Foundation design is done for the allowable bearing capacity. Foundation can reach its ultimate bearing capacity for the ultimate loads applied to form the structure.

There are three methods that shallow foundation failure occurs.

• General Shear Failure
• Local Shear Failure
• Punching Shear Failure

Let’s discuss each type of failure in detail.

General Shear Failure

A gradual increase in the load on the foundation will increase the settlement of the footing and increases the pressure under the foundation.

When the pressure under the foundation reaches the ultimate pressure that soil can bear, the foundation will fail suddenly.

These types of foundation failures occur in low compressible soils.

The ultimate pressure that soil can bear is the ultimate bearing capacity of the foundation. As indicated in the above, when the load reaches the ultimate bearing capacity q_u, it fails.

• This types of shallow foundation failure occur in dense sand or stiff cohesive soil.
• Dense and stiff soils are low compressible leads to shear failure.
• Tilting of foundation occurs when fail.

Local Shear Failure

Local shear failures occur in medium compaction soil.

An increase in the pressure in the foundation increases the settlement of the foundation and the failure surface in the soil gradually extent outwards from the foundation.

Failure surface does not extend to the ground surface as the soil is compressible or due to the deeper depth of the foundation.

Punching Shear Failure 

This type of shallow foundation failure occurs when the foundation is rested on fairly loose soil where the settlement of the foundation is higher.

Shear surfaces are not developed due to the compressibility of soil.

The soil under the foundation compressed and it cannot bear the pressure applied from the foundation.

The above figure indicates the failure surface and the load settlement curve of the foundation.

The article ground improvements could be referred for methods of improving the ground condition to have a higher bearing capacity.

In addition, reading the article on how to determine foundation type could be useful to know the methods to determine the foundation type.