Unsaturated fine-grained soils subjected to cyclic railway loading exhibit pronounced nonlinear behavior, characterized by permanent settlements, shear modulus degradation (stiffness softening), and progressive accumulation of shear strains. In this study, a three-dimensional numerical modeling framework was developed using the Abaqus finite-element platform. The numerical outcomes were validated against the benchmark Ledsgaard and Hall dataset at depths of 2.5 and 7.7 m, demonstrating a satisfactory correlation based on calculated statistical indices. The principal innovations of this work are fourfold: (i) layer-by-layer calibration of the elastic modulus according to the shear strain computed for each individual stratum to accurately capture the non-uniform stiffness degradation across depth; (ii) a practical and streamlined approach to simulate plastic soil response via the direct reduction of the elastic modulus, which dramatically decreases computational expense; (iii) proven adaptability to the fine-grained soils of northern Iran, as corroborated through comparison with Hesami's earlier findings; and (iv) the flexible definition of distinct loading scenarios pertinent to Iranian railway infrastructure, encompassing both high-speed passenger and heavy-freight operations. The results indicate that the proposed model curtails the total analysis time from over 100 days to roughly 3 hours. Consequently, this framework furnishes an efficient and robust analytical tool for railway track designers and engineering geologists engaged in foundation assessment and ground improvement.