Comparison of 2D and 3D Slope Stability Analysis Using Limit Equilibrium Method

In slope engineering, two-dimensional (2D) limit equilibrium methods are most common. Two-dimensional slope formulation has been done based on the assumption that plane strain conditions are applicable. However, if plane strain assumptions are invalidated, 3D slope analysis becomes unavoidable. It would be interesting to observe the difference between 2 and 3D slope analysis for any slope to study their mechanisms. In the present work, a homogenous soil slope is analyzed using both 2D and 3D formulations based on Bishop’s simplified method (BSM). The digital elevation model (DEM) approach is used to build the slope’s 3D geometry. The nature of failure surfaces, the distribution of normal force along the base of the failure surface, m-alpha (mα), and the variation of base dip angles are plotted. The results indicate that 2D slope analysis usually yields conservative estimate of factor of safety (FS) than the 3D analysis. It is considered that 2D slope stability analysis always gives a more conservative estimate of the three-dimensional (3D) slope stability problem.