<p>Pile foundations are widely used to transfer loads through weak soil layers to stiffer strata to ensure overall stability. Given their critical role in buildings, offshore and transportation infrastructures, especially in seismic-prone areas, it is essential to understand the seismic behavior of pile-supported systems. In modern geotechnical practice, ground improvement is increasingly adopted to enhance subsoil performance. However, the effectiveness of ground improvement in terms of system seismic response, particularly in clayey soils, remains underexplored. In this regard, this study employs three-dimensional nonlinear time-domain numerical analyses to evaluate the seismic performance of pile foundations. The model incorporates a nonlinear advanced constitutive framework that accounts for stress-dependent stiffness and strength, as well as cyclic degradation captured via a nonlinear kinematic hardening model to realistically simulate soil behavior. A parametric study investigates how the use of ground improvement influences seismic performance across varying earthquake frequencies. Results of this study indicate that for earthquakes with low frequency content, ground improvement significantly enhances seismic performance by reducing pile bending moments, lateral displacements, and shear forces. However, for earthquakes with high frequency content, the increased soil stiffness and strength due to improvement can amplify these pile response parameters, potentially compromising seismic performance. Additionally, the influence of pile diameter on peak bending moment was also discussed. These results provide practical guidance for the effective use of ground improvement in seismic foundation design and highlight the importance of material selection and behavior in enhancing infrastructure resilience in seismic-prone areas.</p>