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Which of the following is a characteristic of general shear failure?
Failure is accompanied by compressibility of soil
Failure is sudden
Bulging of shearing mass of soil
All of the mentioned
Bulging of shearing mass of soil
General shear failure occurs in dense sand or stiff clay under a shallow foundation when the soil fails along a continuous and well-defined failure surface that extends up to the ground level ┬╖ A key characteristic of general shear failure is the noticeable bulging of the shearing mass of soil adjacent to the footing, accompanied by a sudden catastrophic collapse and visible tilting of the structure.
General shear failure occurs in dense sand or stiff clay under a shallow foundation when the soil fails along a continuous and well-defined failure surface that extends up to the ground level ┬╖ A key characteristic of general shear failure is the noticeable bulging of the shearing mass of soil adjacent to the footing, accompanied by a sudden catastrophic collapse and visible tilting of the structure.
quтАЛ=cNcтАЛ+qNqтАЛ+0.5╬│BNgтАЛamma тАФ Terzaghi's ultimate bearing capacity equation for general shear failure
DrтАЛ>70% тАФ Relative density condition for dense sand where general shear failure typically occurs
When a load is applied to a foundation resting on dense or stiff soil, the soil deforms elastically until the maximum shear strength is reached along a defined failure plane ┬╖ Upon reaching ultimate bearing capacity, a wedge of soil beneath the footing moves downward, forcing the adjacent zones to move laterally and upward, causing pronounced heave or bulging at the ground surface.
General shear failure occurs in soils of low compressibility, such as dense sand (DrтАЛ>70%) and stiff clay (NSPTтАЛ>30).
It is characterized by a clear ultimate failure point on the load-settlement curve and sudden catastrophic failure with structural tilting.
A continuous shear plane forms and extends all the way to the ground surface, resulting in prominent surface bulging/heaving.
| Feature | General Shear Failure | Punching Shear Failure |
|---|---|---|
Soil Type & Density | Dense Sand (DrтАЛ>70%) / Stiff Clay | Loose Sand (DrтАЛ<30%) / Soft Clay |
Failure Surface | Well-defined, extends to ground surface | Poorly defined, localized under footing |
Surface Bulging/Heave | Significant bulging on sides of footing | No bulging observed at ground surface |
Failure Nature | Sudden, accompanied by tilting of footing | Gradual, characterized by deep vertical penetration |
Option A is incorrect because soil compressibility is a major characteristic of local and punching shear failures in loose or compressible soils, not general shear failure.
Option B is true regarding the sudden nature of general shear failure, but Option C is a distinct and definitive physical characteristic (bulging of shearing mass), making Option C the specified correct answer.
C is correct тАФ General shear failure involves the lateral displacement of soil along a continuous slip surface, which forces the adjacent soil mass to bulge upward at the ground surface.
For GATE and ESE exams, remember that for local shear failure, shear parameters are reduced (cтА▓=32тАЛc and tan╧ХтА▓=32тАЛtan╧Х), whereas general shear failure uses full shear parameter values.