Test: Stability of Earth Slopes - Civil Engineering (CE) MCQ

For an infinite slope in cohesionless soil.


For ϕ > i F > 1 it means that the slope remains stable as long as angle of slope is less than angle of shearing resistance.

The factor of safety of slope against shear failure is given by  from which
if ϕ = β; slope is just stable
ϕ < β; slope is unstable
ϕ > β; slope is stable

Taylor’s stability No.

∴
​∴

Stability number,

The factor of safety with respect to shear strength is given by,

The shear strength mobilised, thus may be written as,



 

Face failure or slope failure can occur when the slope angle β is very high and the soil close to the toe is quite strong or the soil in the upper part of slope is relatively weak.
Base failure can occur when the soil below the toe is relatively weak and soft and the slope is flat. Toe failure occurs in steep slopes when the soil mass above the base and below the base is homogeneous.

The Correct Option is C: Mobilised angle

In Taylor's stability number curves, the angle of shearing resistance used is the mobilized angle. The mobilized angle of shearing resistance represents the actual angle at which the soil is resisting shearing forces during slope stability analysis. It takes into account factors such as pore water pressure and soil deformation. The mobilized angle is an important consideration when analyzing the stability of slopes and designing appropriate measures to ensure stability.

For slopes greater than 53°, the critical slip circle invariably passes through the toe. (Toe failure). This is true for any angle of friction (ϕ).
For slopes less than 53° and small values of ϕ < 3°, the critical surface passes below the toe and it is called base failure.