Advanced calculations of safety factors for slope stability

With the fast progress of FE codes targeting geotechnical engineering, a so-called phi-c-reduction method is becoming widely used for the determination of the slope stability factors. It has been shown that this method yields comparable results with the traditional slice methods in case of simple slope geometries and ground conditions. However, its application is limited to the Mohr-Coulomb limit stress condition and thus this method neglects the influence of stress and deformation level on the shear strength of soils. This contradicts experimental evidence and may lead to an unsafe design. The paper analyzes the sensitivity of the phi-c-reduction method and shows the influence of stress-dependent shear strength on the calculated factor of safety and on the geometry of the critical slip surface.