Types of Shear Failures in Soils

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Types of Shear Failures in Soils

Shear Failures in Soils are categorized into three primary classes: general shear failure, local shear failure, and punching shear failure.

  1. General Shear Failure: This is the most frequent type of shear failure. It occurs when the soil beneath a footing cannot support the load placed on it. The failure surface is well-defined and extends from the edge of the footing to the ground surface. Characterized by sudden collapse, tilting of the footing, and bulging of the soil surface. It’s common in dense and stiff soils that undergo low compressibility. i) Upon the increase in stress, settlement of soil will not take place, stresses in the soil near footing will keep on increasing with increasing the load. ii) Gradually, zones of failures will develop completely. iii) Soil will change its state from elastic to plastic state. iv) In plastic state, volumetric strain will be high, hence volume increase will cause bulging, v) Significant amount of bulging/ heaving at G.L will take place. vi) When max. c and φ are mobilised then, soil will fail in shear causing slipping of footing and will cause overturning of footing. vii) Failure will be because of overturning and not because of settlement.
  2. Local Shear Failure: This type of failure appears in relatively loose and soft soils. The failure surface is not as well-defined as in general shear failure and is located only under the footing. It’s not as catastrophic as general shear failure but can still cause damage to the footing and surrounding soil. It’s characterized by significant compression of soil below the footing, partial development of plastic equilibrium, slight bulging of soil around the footing, and considerable settlement. It’s accompanied by large strains (>10 to 20%) in a soil with low density (ID<20%), low cohesion angle (<28°), and low normal stress (N<5).
  3. Punching Shear Failure: This type of failure is seen in loose and soft soils at deeper elevations. The failure pattern is not observed, bulging of soil around the footing is absent, and it’s characterized by very large settlements. Continuous settlement with no increase in pressure is observed in the curve. It occurs in a soil of very high compressibility.

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Arbaj Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

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