FEM Modelling of Thin Weak Layers in Slope Stability Analysis

Modelling the presence and the effect of a thin weak layer of soil or rock in a slope stability analysis performed through the finite element method (FEM) presents several problems of purely numerical nature. This paper deals with a parametric analysis of three different 2D numerical case studies (both ideal and real) of unstable or potentially unstable slopes containing a thin soft band (or weak layer). The FEM software used is RS2 (Rocscience (R)). The aim is investigating the influence of some geometrical and numerical characteristics of the soft bands in the stability analyses. The MohrCoulomb elastic-perfectly plastic constitutive model for all the involved materials was assumed, and the mechanical parameters were kept constant. Instead, other fundamental parameters of the weak layer, such as the type of mesh elements, the mesh density, and the geometry, in terms of both thickness and outcrop shape, were changed, and results in terms of the critical Strength Reduction Factor (SRF) were compared. The main outcomes of this study represent practical suggestions on some numerical and technical aspects to users of FEM slope stability analyses, in order to obtain a precautionary assessment of slope stability.