Spatial Distribution Characteristics of Dynamic Displacement of Heavy-Haul Railway Subgrade System under Launching Impact Load

To study the spatial distribution characteristics of dynamic response of military heavy-haul railway subgrade, using highly nonlinear analysis program ANSYS/LS-DYNA3D, a 3D explicit dynamic model of a track-subgrade-foundation system was established with the 3D consistent viscous-spring artificial boundary. The trapezoidal impulse load was used to simulate the launching impact load, and spatial distribution characteristics of the dynamic displacement of the subgrade system under loads of different amplitudes (150−600 kN) were discussed. The model reliability was then verified by Boussinesq elastic theory and Lin Xiuxian ’s multi-layer system equivalent theory. The results indicated that the vertical dynamic displacement of the subgrade system reaches the maximum value when the launching impact load on the track starts to unload. At the end of unloading, there is a certain amount of residual deformation in the top surface of the ballast bed, and the residual deformation increases linearly with an increase in load amplitude, and the growth rate is about 0.6 × 10⁻² mm/kN. Under different load amplitudes, the dynamic displacement of the subgrade system is distributed symmetrically both laterally and longitudinally along the line, it decays linearly along the vertical direction, and the decaying rate increases with the increase of the load amplitude. The larger the load amplitude is, the more significant the wheelset effect of dynamic displacement and the contribution of ballast bed and subgrade bed to rail dynamic force are; the peak dynamic displacement of subgrade system is approximately linear with the load amplitude. With the increase of the load amplitude, the peak dynamic displacement of the ballast bed surface grows at the fastest rate of about 1.27 × 10⁻² mm/kN, followed by the peak value of the subgrade bed surface and the subgrade bed bottom at growth rates of about 1.23 × 10⁻² and 1.20 × 10⁻² mm/kN, respectively, and the peak value of the subgrade body grow at the slowest rate of about 1.10 × 10⁻² mm/kN.