Rockfill materials experience gradual deformation over time, which can cause serious problems in rockfill structures, especially in dams. This deformation may lead to reduced confinement of the dam core by the shells, resulting in large deformations within the dam body, as well as cracking in filters and core, a loss of freeboard, and damage to associated facilities. The creep behavior of rockfill materials is influenced by various factors, such as stress level, material composition, aggregate shape, particle size, and moisture content. This study presents the application of the Soft Soil Creep model to simulate both volumetric and shear creep in rockfill materials. The model parameters were determined from large-scale oedometer tests using an integrated procedure that combines experimental data with numerical back-analysis, ensuring a physically consistent parameter set. Furthermore, the study analyzes the influence of these parameters on rockfill behavior, highlighting their role in controlling the creep deformations. As a case study, the creep behavior of the rockfill shells in the 177-m-high Masjed Soleyman Dam is investigated. The study confirms the model reliability in predicting dam settlement patterns through comparison with measured data and observations. Localized computed shear strain in upper level of the dam exceeded 50 % aligning with what accrued in the prototype.