Test: Types of Bearing Capacity Failures - Civil Engineering (CE) MCQ

In general shear failure, when the pressure approaches the value of qf, the state of equilibrium is reached initially in the soil around the soil and gradually spreads, ultimately the state of plastic equilibrium is fully developed throughout the soil above the failure surfaces.

In local shear stress there is no tilting of footing and therefore the failure is not sudden.

Punching shear may occur in relatively loose sand with relative density less than 35 %.

General shear failure

Occur in medium to dense soil and stiff clays and has the following properties:

a) A well – defined failure pattern

b) Sudden, catastrophic failure accompanied by tilting of foundation

c) Bulging of the ground surface adjacent to the foundation.

This occurs in soils that show brittle – type stress-strain behavior.

In 1963, Vesic observed three types of bearing capacity failures:
i) General shear failure
ii) Local shear failure
iii) Punching shear failure.

Experimental investigations have indicated that when a footing fails due to insufficient bearing capacity, distinct failure patterns are developed, depending upon the type of failure mechanism.

In the case of general shear failure, continuous failure surface develops between the edges of the footing and the ground surface.

Local shear failure: This type of failure is seen in relatively loose sand and soft clay.

Some characteristics of local shear failure are:

1. Failure is not sudden and there is no tilting of footing.

2. Failure surface does not reach the ground surface and slight bulging of soil around the footing is observed

3. Failure surface is not well defined

4. Failure is progressive

5. In the load-settlement curve, there is no well-defined peak

6. Failure is characterized by considerable settlement directly beneath the foundation

7. Significant compression of soil below the footing and partial development of plastic equilibrium is observed.

8. Well-defined wedge and slip surface only beneath the foundation.

Local shear failure occurs in soil having high compressibility and in sands having relative density lying between 35 and 70 percent.

In local shear failure there is a significant compression of the soil under the footing and only partial development of state of plastic equilibrium. Due to this reason, the failure surface does not reach the ground.