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Local shear failure is associated with soils having _________
High compressibility
High pore pressure
Low porosity
Low compressibility
High compressibility
Local shear failure is a mode of soil failure observed primarily in loose sands or soft, highly compressible clays ┬╖ Unlike general shear failure, it is characterized by significant settlement before the ultimate bearing capacity is reached, with a failure surface that does not extend to the ground surface.
Local shear failure is a mode of soil failure observed primarily in loose sands or soft, highly compressible clays ┬╖ Unlike general shear failure, it is characterized by significant settlement before the ultimate bearing capacity is reached, with a failure surface that does not extend to the ground surface.
quтАЛ=32тАЛcNcтА▓тАЛ+qNqтА▓тАЛ+0.5╬│BN╬│тА▓тАЛ тАФ Vesic's equation for local shear failure where c,╧Х are reduced to 32тАЛc and tanтИТ1(32тАЛtan╧Х).
As the load increases, the soil under the footing undergoes local compression and densification ┬╖ Because the soil is highly compressible, it cannot maintain the equilibrium required for a continuous failure surface to propagate to the surface ┬╖ Consequently, the soil below the footing is compressed, resulting in gradual tilting or sinking without a sudden, catastrophic collapse.
Local shear failure occurs in soil with high compressibility or loose density.
The failure surface is not well-defined and does not extend to the ground surface.
Significant settlement is observed before the ultimate bearing capacity is reached.
Reduced shear strength parameters are used for design calculations.
Predictable settlement behavior in soft soils
Prevents sudden catastrophic failure in building foundations
Requires larger footing sizes due to lower bearing capacity
Complex to analyze compared to general shear failure
Foundations on loose sand deposits
Construction on soft, saturated sensitive clays
| Feature | General | Local |
|---|---|---|
Failure Mode | General Shear | Local Shear |
The relative density (DrтАЛ) for soils prone to local shear failure is typically less than 30%.
Option B (High pore pressure) leads to undrained failure but is not the defining cause of local shear failure mode ┬╖ Option C and D represent soils prone to general shear failure.
A is correct тАФ Local shear failure occurs in highly compressible soils where the soil densifies under the footing rather than forming a continuous slip surface to the surface.
Always remember that in loose sand (DrтАЛ<30%) and soft clay, we apply reduction factors to c and ╧Х to account for the local shear failure effect.