Non-convergence criterion on slope stability FE analysis by strength reduction method

Elasto-plastic finite element analysis (FEA) by using strength reduction method (SRM) is carried out to achieve the slope stability and the corresponding critical failure mechanism. Iterative non-convergence criterion for evaluating the slope instability state in FE numerical calculations is proposed and is compared with the conventional criteria, combined with two typical 2D and 3D slope examples. A large number of computed processes and results demonstrate that when a slope arrives at the critical failure state by FEA using SRM, the four instability criteria as plastic zone extension from the toe to the top of slope, equivalent plastic strain exceeding a certain value developed along the potential slip surface, uncontrollable increase in characteristic nodal displacement on slope surface, and non-convergence of solutions can be found in turn, and the obtained factors of safety and critical failure surfaces based on four instability criteria are very close to each other. Moreover, non-convergence criterion is fit for coding the program with automatic searching the factor of safety as well as being less dependent on users' experience, and is readily to operate in practice. Based on non-convergence criterion, the effect of element types, mesh size, soil properties on the factor of safety and critical slip surface are respectively discussed. The results show that the bigger cohesion, smaller friction angle or the lower slope angle can make slip surface deeper, and the out-slip point is far from slope toe.