Slope stability concepts
If there are loading outside the toe that prevent the circle from passing below the toe, the long dashed curved should be used to determine the developed cohesion. Note that the solid and the long dashed curves converge as n approaches zero. The circle represented by the curves on the left of n = 0 does not pass below the toe, so the loading outside the toe has no influence on the developed cohesion.Taylor's ChartStability assessments of earth slopes require limit state calculations,which differ significantly from those in structural engineering.This is because the weight of the soil constitutes the mainload on slopes, yet it contributes to forces both resisting and drivingthe collapse. These forces depend on the mode of failure andthe particular geometry of the failure mechanism. Consequently,the safety factor cannot be defined as a ratio of the limit load tothe working load ~both being ill-defined for slopes!, but is usuallydefined as a function of the strength of the soil. Typically, thestrength of the soil is described by the Mohr–Coulomb yield conditionas a function of the cohesion, c, and the internal frictionangle, w. A common definition of the factor of safety ~F! is theratio of the shear strength of the soil to the shear stress necessaryto maintain limit equilibrium
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