To systematically investigate the influence of different pile types on the failure modes and overall stability of embankment supported by composite foundations, a three-dimensional finite element analysis method was employed to study pile failure characteristics and the evolution patterns of shear strain in foundation soils. A full lifecycle cost and benefit analysis framework was applied to evaluate the economic performance of various composite foundation configurations, thereby identifying the optimal design strategy with the highest cost efficiency. The results demonstrate that under embankment loading conditions, pile type significantly alters the failure mode of embankment supported by composite foundations. As pile stiffness increases, the failure mode transitions from shear failure to flexural failure, and the failure development pattern shifts from simultaneous failure to progressive failure. Specifically, in gravel pile composite foundations, the plastic shear strain in soils exhibits progressive development along the embankment centerline. In contrast, the shear strain evolution in plain concrete pile composite foundations displays distinct forward propagation at the embankment center and backward propagation at the slope toe region, ultimately forming a continuous critical sliding surface. Compared to strengthening piles across the entire area, installing high-strength piles only beneath the embankment slope toe to the shoulder of the embankment can significantly enhance the overall stability of the embankment, demonstrating superior return on investment and cost-effectiveness.