Numerical Investigation into Hydrodynamic Behavior of Graded Aggregates of High-Speed Ballastless Track Considering the Degree of Saturation

The ballastless track inevitably suffers from some functional defects, such as expansion joint cracking, due to the long term combined effect of dynamic train loads and environmental factors. As a result, water can be somehow retained in the graded aggregates of the roadbed surface layer under ballastless track, which is a key structural component subject to high-speed train loads. Accordingly, it is of significance to study the hydrodynamic behavior of roadbed surface layer that can be prone to depend on variation of the degree of saturation (Sr) in graded aggregates. A coupled hydrodynamic model of roadbed surface layer under ballastless track subject to high speed train loads was established based on homogenization theory and elastic wave theory involving Sr of graded aggregates. The proposed model is validated by degrading to Biot's dynamic model in saturated porous medium and analytical method of unsaturated soil. The effect of different Sr on the pore fluid pressure, spatial seepage velocity of graded aggregates is investigated based on this model with the practical seepage boundaries in ballastless track considered. On this basis, the influence of different spatial locations on the dynamic seepage index is discussed, and the differences in the stress paths in the roadbed surface layer under different Sr at different depths are analysed. The numerical results show that the increase of Sr has a spatial and critical effect on the increase of pore water pressure and seepage velocity in the roadbed surface layer. When the expansion joint of ballastless track cracks, the hydrodynamic erosion in the surface layer of ballastless track roadbed has been accumulating continuously. The erosion is more serious within the depth of 15 cm under the surface of roadbed. For Sr above 0.7, extra attention should be given to prevent internal erosion diseases in the roadbed surface layer during maintenance of ballastless track.