A comprehensive study on 3D slope stability analysis using coupled finite element method and strength reduction technique

Slope stability analysis, traditionally formulated in two-dimensional (2D) under plane strain conditions, requires three-dimensional (3D) analysis where plain strain condition is violated such as in case of corner failures or variations in the longitudinal direction. This study presents 3D slope stability analysis using a Finite Element Method (FEM) program based on the Strength Reduction Technique (SRT). Stress redistribution is achieved through a viscoplastic algorithm, and the Mohr-Coulomb strength criterion is applied to predict stress states. Slope failure is simulated when iterative calculations show non-convergence, indicating that the equilibrium of the forces could no longer be achieved. The program has been validated by analysing problems, including slopes subjected to earthquake forces and water loading, and the obtained result is compared with the results of existing literature. For ponding water, equivalent nodal loads are derived for slopes discretized using 20-noded brick elements. A novel extrapolation method calculates nodal stresses from sampling points, minimizing fitting errors while preserving the trends. Results, such as deformed meshes, contour plots of visco-plastic strain, yield function, and pore-water pressure, illustrate failure states. Comparison with other studies demonstrates strong agreement, confirming the program's accuracy and robustness in capturing complex slope failure mechanisms.