Evaluation of factor of safety for vegetated and barren soil slopes with limit equilibrium computations

Abstract

Limit equilibrium method (LEM) is the most conventional and popular technique in slope stability analysis. Location of the unique failure surface and the determination of corresponding critical factor of safety (critical-FOS) of the soil slope requires a lot of trial and research. With this amount of trial and research results, we evaluate the field of factor of safety (FOS-field), which represents the critical-FOS at a point within the domain of all possible failure surfaces. Such a field can be very important for the precise judgment of the most critical-FOS of the slope and its perturbation. This paper also presents the evaluation of the FOS-field of vegetated slopes, thus providing an analytical way to examine the effect of vegetation on the soil slope stability. We evaluated the stability of vegetated and barren soil slopes under dry and fully saturated conditions. With dry and fully saturated conditions, the behaviour of slopes in most favourable and worst conditions can be simulated. Evaluation of FOS-field for various slope geometries and conditions show that the more unstable the slope becomes, the more difficult it will be to pinpoint the location of the critical failure surface with the unique least FOS. We verified the LEM codes with finite element method (FEM) and spectral element method (SEM) codes considering a sample problem from Smith and Griffiths’ book (Smith and Griffiths 2003).

Keywords:

• slope stability analysis
• limit equilibrium method (LEM)
• vegetated and barren soil slopes
• unique failure surface
• factor of safety field (FOS-field)

Acknowledgements

The authors thank Dr Hom Nath Gharti NORSAR Norway and Prof Padma Bahadur Khadka, Institute of Engineering, Tribhuvan University Pulchowk, Nepal for stimulating effective discussions and suggestions.