## 4 Conclusions  
This study conducted three-dimensional numerical analyses using FLAC3D to assess the seismic response of group pile-supported structures, with emphasis on the interplay between kinematic and inertial effects. A total of 12 simulation cases were developed by varying seismic intensity, soil relative density, and superstructure mass, allowing for a comprehensive evaluation of soil-pile-structure interaction in dry ground conditions. Figure 14: Maximum lateral pile displacement along depths under varying pile cap mass. Figure 13: Maximum lateral pile displacement along depths under varying soil relative densities. 1. The results reveal that kinematic effects become increasingly pronounced with higher seismic input levels, especially under dense soil conditions. While loose soils exhibited relatively large displacements, the difference in pile cap velocity responses between loose and dense soils grew with increasing seismic intensity. This trend confirms that denser soils, although stiffer, transmit stronger kinematic forces during strong seismic events, which can amplify bending moments in the piles and structural demands on the superstructure. 2. The simulations showed that heavier superstructure mass generally leads to increased inertial forces. However, due to the embedment of the pile cap and the confining effect of the pile group system, the manifestation of inertial effects was limited in terms of pile and pile cap displacements. Interestingly, an increase in pile cap mass introduced a resistive interaction with kinematic effects, reducing differential motions and contributing to more synchronized dynamic responses between pile top and bottom in some cases. This interplay was more evident under dense soil conditions and higher input motions. 3. Despite varying soil conditions and seismic intensities, the absolute magnitude of pile displacements remained relatively small (less than 5 mm at pile tops), suggesting limited impact on serviceability for pile group systems with embedded pile caps under dry ground conditions. However, from a structural stability perspective, attention must be paid to stress accumulation in the piles, particularly under dense soil conditions where internal forces intensify due to stronger kinematic interactions. Furthermore, while the current study focuses on dry soil environments, significantly different behavior is anticipated in liquefiable soils, where factors such as strength degradation and lateral spreading can dominate the response. In conclusion, this study provides valuable insights into the dynamic behavior of pile-supported structures by analyzing the coupled effects of kinematic and inertial forces in a three-dimensional framework. In general, the effect of kinetic force is expected to be large in loose soil (large displacement during earthquake) such as liquefied soil, but it was identified that the effect of kinetic force in dense soil could be more prominent in dry soil conditions when the magnitude of the earthquake is large. In addition, it was identified that the interaction of inertial force and kinetic force acts in the direction of reducing the difference in behavior between the top and bottom of the piles in the condition of pile cap-embedded group piles and that a more economical design is possible when considering this when the superstructure mass increases. The findings emphasize the importance of considering both soil stiffness and structural mass when evaluating seismic performance and highlight the necessity of tailored design strategies for varying ground conditions. These results can inform more robust seismic design guidelines and serve as a basis for future research involving complex soil-structure interaction phenomena under liquefaction or multi-directional loading scenarios.