Question

What type of mode of failure is seen if footing is resting on very dense sand, loaded by transient dynamic loads?
1. Local shear failure
2. General shear failure
3. Punching shear failure
4. Flexural failure

Answer 1

Correct Answer - Option 3 : Punching shear failure

Explanation:

Types of shear failure:

General shear failure:

• It occurs in shallow foundations when placed on dense/stiff soil.
• At the time of failure, the foundation will get tilted and heaving will occur at the side.
• Before failure settlement will be small and negligible and the stress zone extends up to ground level. 

​Local shear failure:

• It occurs in loose sand and soft clays in case of shallow foundation.
• Before failure large settlement is recorded.
• The stress zone does not extend up to the ground level hence there may e little or no heaving at the sides.

Punching shear failure:

• It occurs in deep footing and pile which are placed on loose sand or soft clays.
• In this failure soil below the foundation gets cut off from adjacent soil by shearing and large settlement is recorded in the small-time period.
• The adjacent soil mass remains unstressed.
• Mode of failure is seen if footing is resting on very dense sand, loaded by transient dynamic loads

Foundation condition	Types of shear failure
Footings on the surface or at shallow depths in very dense sand	General shear failure
Footing on saturated and normally consolidated clay under undrained loading	General shear failure
Footings at deeper depth in dense sand	Punching shear failure
Footing on the surface or at shallow depths in loose sand	Punching shear failure
Footing on very dense sand loaded by transient dynamic load	Punching shear failure
Footings on very dense sand underlain by loose sand or soft clay	Punching shear failure
Footing on saturated and normally consolidated clay under drained loading	Punching/Local shear failure