Types of shear failure of foundation of soil

1. General shear failure

• This type of failure is seen in dense sand or silt or over consolidated clay
• It always occur in shallow foundation
• The failure surface develops between the edge of footing and ground surface
• This failure occur in low compressible soil
• Tilting of foundation occur in one side only
• Stress zone will get extend upto ground level
• The strain develops is less than 5%
• The relative density or density index (ID) is less than 70%
• The value of  is always less than 36o  (>36o) 
• The void ratio is less than 0.55
• The standard penetration value is greater than 30

   2. Local shear failure

• This type of failure occurs in loose sand and soft clay in shallow footing
• Stress zone does not reach upto ground surface and little bulging of soil around footing is observed
• There is no tilting of footing     
• The failure surface is not well defined
• The void ratio is greater than 0.75
• The standard penetration value is less than 5
• The relative density or density index (ID) is varies between 30% to 70%
• The strain is varies from 10% to 20%
• The value of  is  less than 28

   3. Punching shear failure

      

• This type of failure occurs in deep foundation or soil of very high compressibility
• In this failure soil below foundation get cut off from the adjacent soil by shearing and excessive settlement is recorded  
• Clear failure is not observed hence ultimate bearing capacity is not well defined
• Bulging of soil is absent in this failure