This paper examines the results of numerical simulation of the stress-strain state (SSS) in a rockfill dam 235 m tall, with a massive three-tier grout curtain used as the impervious element. Calculations were done for multiple scenarios that reflected the wide range of possible changes of the modulus of deformation for the filler rock and cemented soil (200 MPa to 5000 MPa). The author’s original computation program was used in order to consider the elastoplastic behavior of soil. It was discovered that a super-tall dam with a vertical rigid impervious element features an adverse SSS: the hydrostatic pressure in the head reach gives creates a sliding wedge in the upper retaining prism. As the dam has rigid structure, this causes marginal state zones in the filler rock. Only when deforming ability of the filler rock is very low (deformation modulus above 300 MPa), the dam’s SSS may be acceptable. Strength characteristics of the grout curtain were evaluated based on stresses that emerge after it is created. The SSS of the grout curtain is mainly described by bending strains. In case of low deforming ability of the screen material, this can give rise to fissures in the screen material where it contacts the bedrock base. Strength and water impermeability of the grout curtain are secured only after bentonitecement slurry is injected to make the deforming ability of the screen material and filler rock comparable.