This study aims to determine the effect of using stone columns (S.C.) for stiffness improvement of weak subgrade below a double-line (DL) railway track system using the 3D finite element method. Subgrade, ballast, and sub-ballast are modeled as Mohr–Coulomb material. Sleepers and rails are considered as linear elastic. Symmetric conditions are analyzed by considering the same loading and boundary conditions for both tracks to reduce the computational time. The X-2000 train load is simulated for a speed of 250 km/h. A significant reduction in the vertical displacement of the subgrade is observed due to the introduction of stone columns. A parametric study is conducted to study the effect of loading conditions and geometric and material properties of stone columns on settlement characteristics of the reinforced track system. The applied load, velocity, length, and spacing-to-diameter ratio of stone columns significantly affected the performance of stone columns as the reinforcing material. The effect of stiffness of the stone column was noticeable only for very soft subgrade.