Principal modes of shear failure Under Footing

Principal modes of shear failure under Footing

(1) General Shear Failure: These failures occurs generally under the narrow footings of the shallow depths resting on a dense and almost incompressible soils. 

(2) Local Shear Failure: For weaker, more compressible soil and wider or deeper footings, the failure may be taken as local shear failure or punching shear failure. local shear failure is characterized by well defined slip lines below the footing but extending up to short distances in the soil mass.

(3) Punching Shear Failure: It occurs in highly compressible soils. This is characterized by lack of well defined slip lines. Vertical movement of the footing is primarily due to the compression of the soil below the footing with the soil on  the sides not being involved.