Abstract: Pile-net composite embankments are more and more widely used in high-speed railways construction, but the response mechanisms under the dynamic train load are still unclear. In this paper, a large-scale X-pile-net composite embankment model is established, and the dynamic response characteristics of a system consisting of subsoil, X-piles, reinforced cushion, the embankment, and track slab are investigated. The results show that as the train speed and axle load increase, the response amplitudes of the dynamic earth pressure, dynamic displacement, dynamic strain, and vibration speed increase as well. Due to the reflection of M-shaped wave at the interface between the pile tip and subsoil, the dynamic earth pressure exerted on the pile is larger than that on the pile. Compared to the embankment without piles and nets, the reduction effect of vibration on the piled embankment is remarkable. The increase in the dynamic strain of the geogrid above the pile is about 2 times that of the geogrid above the subsoil between of two piles. The transient dynamic strain in the middle and bottom of X-pile is larger. At the same location, the influence of loading frequency on the vibration velocity is much greater than that of loading amplitude. Compared with the surface of embankment, the increase in vibration velocity within the piled embankment is more affected by the loading frequency. The phenomenon of "resonance-like" has been detected in the embankment above the subsoil, which could be avoided by changing the rigidity of the embankment when building railways.

Key words: dynamic response, high-speed railways, piled embankment, X-pile