Computational investigations of the complex flow and deformation processes of natural slopes within a continuum-mechanical approach become more and more important due to an increasing number of slope movements and slope failure situations caused by heavy rainfall events. Numerical simulations of hillslopes can support the detection of various coupled failure mechanisms by simply changing the initial and boundary conditions of the considered initial-boundary-value problem. This procedure can contribute to a deeper and better understanding of various complex slope failure processes. In this study, the slope system, generally understood as an unsaturated soil, was considered as a triphasic material consisting of a soil skeleton, such as sand, a pore liquid, such as water, and a pore gas, such as air. The model was embedded in the well-founded theory of porous media, while numerical solutions were realized by use of the finite-element solver PANDAS. Proceeding from cohesionless sand as the basic soil under study, the material parameters governing the soil behavior were taken from triaxial experiments on dry sand specimens performed under homogeneous loading conditions, whereas the parameters governing the hydraulic behavior were determined by experiments on saturated soil specimens under nondeforming conditions. Furthermore, numerical investigations of slope failure scenarios under different loading conditions were compared with each other to find out how the pore water influences the failure behavior. The computations reveal a strong coupling between the soil deformation and the hydraulic behavior during failure processes. Finally, the flow and deformation behavior of the natural Heumoes slope in Ebnit situated near Dornbirn in the eastern part of the Voralberg Alps (Austria) was studied qualitatively. Unfortunately, this slope is still in motion.