Three-dimensional slope stability study is preferable to 2D stability assessments since all slopes are three-dimensional. Based on 3D extensions of the ordinary slice method and simplified Bishop's method, this study presents 3D slope stability analysis results for homogenous and heterogeneous soil slopes. The geometry of the slope is built with the help of the Digital Elevation Modelling (DEM) technique. Both the ordinary column method (OCM) and simplified Bishop's method (SBM) in 3D satisfy the moment equilibrium of the failure mass. The obtained FS values for all three problems match the published results closely. The effects of pore water pressure applications and seismic loadings are further investigated by considering different combinations. The pore pressure ratio (ru) and horizontal seismic coefficient (keq), with values ranging from 0.25 to 0.50 and 0.05 to 0.10, respectively, have been considered in the present analysis. The detailed variations of normal and shear forces acting on the base of the 3D columns, as well as the variations of other important parameters such as true dip angle and apparent dip angles along the longitudinal and lateral direction of the failure surface, are shown to highlight the mechanisms of generation of internal forces inside the failure mass, both along longitudinal and lateral directions of the slope. The plots of normal and shear forces along the longitudinal direction of the slope follow a symmetric distribution. In contrast, these plots along the lateral direction of the slope follow an asymmetric profile. It is further seen that when pore pressure and earthquake forces are considered, the normal forces increase, and the mobilised shear forces decrease along both longitudinal and lateral directions of the 3D slope.
