Types of Failure (A) General Shear Failure (B) Local Shear Failure (C) Punching Shear Failure
(A) General Shear Failure
- Continuous, well defined and distinct failure surface develops between the edge of footing and ground surface. Dense or stiff soil that undergoes low compressibility experiences this failure. Continuous bulging of shear mass adjacent to footing is visible. Failure is accompanied by tilting of footing.Failure is sudden and catastrophic with a pronounced peak in curve. The length of disturbance beyond the edge of footing is large. The state of plastic equilibrium is reached initially at the footing edge and spreads gradually downwards and outwards.
(B) Local Shear Failure
- Significant compression of soil below the footing and partial development of plastic equilibrium is observed.
- Failure is not sudden and there is no tilting of footing.
- Failure surface does not reach the ground surface and slight bulging of soil around the footing is observed.
- Failure surface is not well defined.
- Failure is characterized by considerable settlement.\
- The well-defined peak is absent in curve.
- Local shear failure is accompanied by large strain (> 10 to 20%) in soil with considerably low (<28o) and low N (N < 5) having low relative density (ID> 20%).
(C) Punching Shear Failure
- This type of failure occurs in soil of very high compressibility.
- Failure pattern is not observed.
- The bulging of soil around the footing is absent.
- Failure is characterized by a very large settlement.
- The continuous settlement with no increase in P is observed in curve.