Lateral strength and critical depth in infinite slope stability analysis

Infinite slope method is the simplest limit equilibrium method for slope stability analysis. It gives reliable results for slides where the longitudinal dimension prevails on the depth of the landslide. Usually results are conservative since not accounting for the effects of the strength along lateral bounds. Starting from an infinite slope analysis accounting the effects of the shear strength along lateral bounds a simplified rectangular cross section, hHere a new expressions of the factor of safety areis introduced, evaluated in a similar way but by an infinite slope analysis accounting for the effects of the shear strength along lateral bounds assuming using an elliptical and a parabolic cross section of the landslide body. The safety factor evaluated in this way can be quite different from those returned by the classic infinite slope model formula, in particular when the width of the landslide is narrow with respect to its depth and the ratio between the width and the depth of the landslide is lower than 5. An interesting implication of the proposed model is that if cohesion is different from zero, there is a “critical depth”, where the safety factor has a minimum value.