###### Abstract
Analytical, numerical, and experimental methods have been conducted to investigate the mechanical behavior and dynamic interactions of piled raft foundations subjected to dynamic load [21; 22; 23; 24; 25]. [PERSON] et al. [23] presented a substructuring method-based soil structure interaction (SSI) analysis model to study the dynamic impedances of a piled raft (PR) in homogeneous and layered soil conditions. [PERSON] et al. [26] presented physical model tests on a ballastless track supported by a XCC pile-raft foundation, to investigate the vibration velocity on air-dried and saturated sand subsoils. The test results showed that the vibration velocity in a BTXPR foundation is closely related to the degree of saturation of the subsoil. The above scholars performed detailed studies on pile-supported embankment under dynamic loading and provided some valuable conclusions. However, theoretical, numerical, and experimental studies on the dynamic response character, load transfer mechanism, and pile-soil interactions of pile-supported foundations under dynamic loading are fewer than that of static loading, and very limited attention has been paid investigation of their vibration characters and behaviors under moving train loads. Vibration transmission is a complex process for railway track and pile su-ported embankment modeling because of the difficulty in representing the vibration source, the unknown damping coefficients along the propagation path, pile-soil interactions, and the lack of comprehensive information of the substructures. Recently, X-section cast-in-place concrete (XCC), as a new type of noncircular cross-sectional shaped pile, was developed and is widely used in China for soft soil improvement and structural support [26; 27; 28; 29; 30]. The results show that piles with an X-shaped cross section can provide greater bearing capacity than traditional circular piles with the same section area. [PERSON] et al. developed a series of analytical and numerical solutions for capturing the stress transfer mechanism and bearing capacity of XCC pile foundations under a vertical static load [27; 28; 29]. [PERSON] et al. [29] presented physical model tests on a ballastless track XCC pile-raft foundation at a scale of 1/5 under different applied cyclic load frequencies, to investigate the vibration velocity on air-dried and saturated sand subsoils. The test results showed that the vibration velocity in a BTXPR foundation is closely related to the degree of saturation of the subsoil. However, most studies conducted so far have investigated the behavior of the XCC pile-raft foundation under static loads, with very limited attention paid to the behavior of the foundation system under dynamic loads. The dynamic bearing capacity, pile-raft interaction effect, frequency response characteristics, and load transfer mechanism of a pile-raft foundation for high-speed railways under moving train loads are still not very clear. In this paper, a series of large-scale model tests and three-dimensional finite element analyses for an XCC pile-raft composite foundation were conducted to investigate the dynamic responses of the XCC pile-raft composite foundation for a ballastless high-speed railway under moving train loads. In the FE numerical simulation, the equivalent moving M-shaped loading wave was used to simulate the moving train load by applying the load on the unit point in the numerical simulation, of which the time and frequency domain features are consistent with the loading waves in the model test. The model tests and FE simulation results are presented and compared regarding the variation of the dynamic velocity to analyze the characteristics of the dynamic response, transmission, and attenuation for the XCC pile-raft composite foundation.