Recently, other method like the artificial neural networks (ANN) has also been developed to study the deformation of soil nailed walls. Although 2D analysis provides valuable insight into the behaviour of nailed slopes, the effect of soil–nail interaction is not adequately considered. have applied strength reduction method in rock slope stability analysis using two–dimensional (2D) finite element program. The strength reduction approach has also been used to solve pseudo-static stability problems in a frictional-cohesive material. This technique is also adopted in several well-known commercial geotechnical finite element or finite difference programs like PLAXIS 2D, SNAIL, ANSYS, FLAC 2D. The strength reduction method (SRM) analysis is the reduction of strength parameters ( ϕ and c) by factor of safety while the body forces due to weight of soil and other external loads are applied until system cannot maintain a stable condition. The calculation of factor of safety using finite element is also possible by using the strength reduction method. Numerical modelling of reinforced slopes by finite element method has proved very useful in prediction of slope deformation, stress analysis, nail pullout resistance, nail forces along nail length, nail force variations with cohesion, angle of friction and lateral movement of slope. The finite element method (FEM) is also used to analyze the failure zone, soil non–linearity and the staged construction effect to predict the actual site conditions. However, rigid finite elements, linear finite elements, non linear programming or special sequential quadratic programming algorithm has also been used to obtain the optimal upper bound solution for structures and geotechnical problems. In the upper bound approach, the kinematically admissible velocity fields are constructed by a rigid element which makes the limit analysis of slope stability suitable for complex conditions such as slopes with complex geometries, profiles, groundwater conditions and complicated loadings. Hence it is not easy to obtain the lower bound solutions for a practical slope problem. The lower bound approach incorporates static permissible stress fields in the analysis, which are usually assumed and do not hold any significant relations to the actual stress fields. In addition to the limit equilibrium method (LEM), researchers have also employed the use of limit analysis which includes an upper bound approach and a lower bound approach. The assumptions are usually focused on inclination or location of the interslice forces and a pre-chosen slip surface of an assumed geometry like log-spiral, wedge and circular. These limit equilibrium methods also known as the ‘method of slices’ is based on the concept of dividing the failure mass into slices, with certain assumptions on the interslice force distribution, for calculating the factor of safety. The stability analysis of reinforced slopes has been carried out by the traditional limit equilibrium approach by many researchers. These reinforced slopes have to be analyzed for stability and their reinforcement methods. The unstable slopes can now be improved and made stable by the use of soil nailing technique. Soil nailing has emerged as an effective ground improvement technique especially in cases of slope instability. The effect of other parameters like bond length in limit equilibrium, soil–nail interaction and bending stiffness in finite element are also studied. Large nail forces are observed by limit equilibrium method for 45° slope with all nail inclinations, whereas for 60° slope angle, finite element method shows an increase in the nail forces. The failure surfaces from both methods are found to vary significantly. The limit equilibrium method is found to yield higher values of factor of safety in comparison to finite element method. A comparative study on stability parameters such as factor of safety, critical slip surfaces and nail forces has been carried out. Both the slope angles and all nail inclinations are taken from the horizontal. The analysis is carried out on two slope angles of 45° and 60°, which are reinforced with nails at three different inclinations of 0°, 15° and 30° respectively. An attempt has been made to bring out the differences in results of reinforced slope stability analysis obtained from SLOPE/W (limit equilibrium based) and PLAXIS 2D (finite element based). This paper aims at the two most common methods used for slope stability analysis.
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