Comparison of Finite Element and Limit Equilibrium Methods for Slope Stability Analysis

Slope stability analysis is one of the most prominent subject matter in geotechnical engineering. Slope may be natural and man-made in its nature, and those slopes can be finite and infinite. It can also be soil mass slope or rock slopes. There are different kinds of slope failures and causes for those slope failures. For those failures, since 1922 by different scholar’s various types of slope stability analysis methods has been discovered. The stability methods can broadly be classified as the limit equilibrium method, the finite element method, the finite difference method and limit analysis method. Limit equilibrium method is the most commonly used methods for analysis. Even though some literatures states that using the finite element method slopes can be analyzed with better accuracy. Therefore, it is better to identify the difference between the two methods more clearly and to identify when to use which method in different circumstances. Thus, the main objective of this project is to compare the limit equilibrium method and the finite element method, to assess their differences and to study when to use which method. Plaxis 2D program has been used for the finite element analysis whereas Slope/W program has been used for the limit equilibrium analysis. Three condition of soil mass was considered, the first one is homogeneous silty sand soil mass, the second one is stratified soil mass and the third one is homogenous clay soil with free surface. The factor of safety value is used as an output for the comparison of the two methods. The analysis result for the homogenous silty sand soil mass shows a Factor of safety value for finite element method is 2.9. whereas for limit equilibrium methods, 3.0 is obtained for ordinary method of slice and 3.19 is obtained for the other types. And similar results are obtained in the other cases. This leads to a conclusion that finite element method is more efficient method for analysis of slope failure than the limit equilibrium methods without a predetermined assumption.