<p>Geosynthetic-encased stone columns (GESCs) are widely used for the treatment of soft soil subgrades in roads and highways, yet their dynamic response mechanism under traffic loading remains insufficiently understood. In this study, combined laboratory model tests and discrete element simulations were conducted to investigate the effects of different bearing strata and encasement materials on the dynamic behavior of GESC composite foundations. The laboratory model tests quantified the settlement and deformation characteristics under cyclic loading, while the numerical simulations provided insights into the microscopic load-transfer mechanisms. The results demonstrated that GESCs reduced the final settlement of composite foundations from over 40&#xa0;mm in unreinforced cases to less than 8&#xa0;mm when high stiffness encasement material end-bearing stone columns were used, with end-bearing stone columns consistently performing better than floating stone columns. High-stiffness encasement materials significantly enhanced bearing capacity and reduced bulging deformation, with the maximum bulging deformation of low stiffness encased columns being more than 17 times that of high-stiffness ones. Failure modes differed with conditions: end-bearing stone columns mainly exhibited bending failure, while floating columns showed punching shear or shear failure depending on the encasement stiffness. Overall, stiffness-matched combinations of encasement material and bearing stratum provided superior bearing capacity and deformation control. These findings clarify the influence mechanisms of key parameters and offer practical guidance for the rational design and long-term stability of GESC-reinforced foundations under vehicular loading.</p>