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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     

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