Variable factor of safety in slope stability analysis by limit equilibrium method

Use of variable factor of safety in slope stability analysis procedures, based on the limit equilibrium method, is presented. The procedure consists of defining a characteristic that describes the variation in factor of safety along a slip surface and the analysis procedure seeks to determine a scalar factor that in combination with the characteristic and the interslice force inclination satisfies boundary conditions in a slope stability problem. The characteristic can be selected by a designer to reflect site-specific conditions. A possible form of the characteristic for frictional materials is discussed. The present practice of using the same factor of safety for the entire shear surface is achieved by making the characteristic equal to unity along the entire shear surface. A case study is included to illustrate the ideas presented.