Foundation-Failure Modes of Shallow Foundations

There are three modes of failure under a shallow foundation. These failures are depending on the compressibility of soil and the depth of foundation relative to its breadth.

General shear failure typically occurs for soils with low compressibility, such as dense coarse-grained or stiff fine-grained soils. This failure mode develops continuous failure surface between the footing edges and ground surface. Ground surface heaves, either on both sides or any one side of the footing. The bearing capacity of footing is well defined under this condition.

Local shear failure surface does not reach the ground surface, and subsequently only slight heaving may occur. This failure is usually occurred in soil with high compressibility, where significant compression of soil takes place.

Punching shear failure occurs when soil is subjected to high compression and the direction of shearing is vertical. No ground surface heaving and tilting of the footing occur under this failure.

Both local shear and punching shear failures do not have well defined ultimate bearing capacity.