Using limit equilibrium concepts in finite element slope stability analysis

This paper reviews the development of finite element slope stability analyses and proposes that such a method can form a practical procedure for solving slope stability problems. Several slope stability methods have been proposed that make use of the finite element methods; these are summarized in this paper. The proposed finite element method is in a form that can be conveniently used in engineering practice. The procedure lends itself to present day numerical modelling techniques. The method has been updated to take advantage of recent advances in computer technology and algorithms. The combination of a finite element stress analysis with a limit equilibrium analysis provides greater certainty and flexibility regarding the internal distribution of stresses within the soil mass. The normal force along any selected slip surface can be calculated from the stress distribution that has been calculated using a linear and non-linear stress analysis. The overall factor of safety for a slope, when the finite element method is used, can be defined as the available shear strength of the soil divided by the resisting shear strength. The overall factor of safety is a combination of the local factors of safety within the slope. The resulting overall factor of safety retains the basic assumptions inherent to the limit equilibrium definition of the factor of safety. The local factors of safety are an expression of the stability of the soil mass at each point along the slip surface. The overall factor of safety computed using the finite element method shows good agreement with the factors of safety computed using any one of several limit equilibrium methods. The finite element method provides additional information regarding the potential performance of a slope; information not available when using traditional limit equilibrium methods. The results indicate that it is important to use the effective shear strength characterization of the soil when performing the slope stability analysis. The computed factor of safety obtained when using a total shear strength characterization of the soil, may not agree with the factor of safety computed when using the finite element stress analysis method.