American Society of Civil Engineers

A Slope Stability Case Study by Limit Equilibrium and Finite Element Methods

by Lei Wei, Ph.D., P.E., M.ASCE, (Geotechnical Engineer, HNTB Corporation, 9100 Bluebonnet Centre Blvd, Suite 301, Baton Rouge, LA 70809 E-mail:, Therese Koutnik, P.E., M.ASCE, (Geotechnical Engineer, HNTB Corporation, 11414 West Park Place, Suite 300, Milwaukee, WI 53224 E-mail:, and Mark Woodward, P.E., M.ASCE, (Geotechnical Engineer, US Army Corps of Engineers, New Orleans District, 7400 Leake Ave, New Orleans, LA 70118 E-mail:
Section: GeoHazard Mitigation Problems, pp. 3090-3099, (doi:

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Document type: Conference Proceeding Paper
Part of: GeoFlorida 2010: Advances in Analysis, Modeling & Design
Abstract: Factors of safety are the primary design criteria used in most slope stability analyses. Traditional limit equilibrium based methods are still widely used in practice while at the same time more and more attention has been paid to finite element based evaluations of slope stability. Shear strength reduction technique is one of the popular methods to compute factor of safety utilizing finite element analysis. Another approach is to calculate the factor of safety using the finite element computed normal and shear stresses along the potential slip surface. This paper presents a case study that used Spencer method, shear strength reduction and directly finite element computed stresses to evaluate the slope stability factor of safety. Spencer method is one of the limit equilibrium based methods that can satisfy all the static equilibrium conditions. Finite element based methods included both shear strength reduction method (SSR) and finite element computed stresses based method (FES). A new shear strength reduction procedure is proposed to determine the factor of safety by examining the yield elements in the finite element results. It is found that the method that directly uses the finite element computed stresses can capture well the relatively deep slip surface. The effect of in-situ stress state on finite element based methods is also briefly discussed.

ASCE Subject Headings:
Slope stability
Finite element method
Limit equilibrium
In situ tests