Dynamic responses of high-speed railway transition zone with various subgrade fillings

In order to explore more economic filling alternatives than typically used graded gravel + 5% cement in a high-speed railway transition zone, engineering properties of graded gravel (without cement) and A, B group filling (well graded coarse-grained soil with less than 30% of fine-grained soil) were tested. This is followed by the establishment of a 3D vertical coupling dynamic model of a tunnel-culvert-tunnel transition section based on the D'Alembert's principle of energy weak variation and the Lagrange scheme. The model results have been validated against the in situ measurements. The analysis from the model show that both graded gravel and A, B group filling are well-graded with high strengths, and the dynamic responses of the roadbed supported by the two fillings are both less than allowable values at the speed of 350 km/h. However, the curves of vertical displacement along the longitudinal transition section are great like a shape of "W" with the A, B group filling in the transition zone. Therefore, the graded gravel is recommended to be more suitable than the A, B group filling for the studied tunnel-culvert-tunnel transition zone. This recommendation may be applicable to the case with a rock subgrade underneath to support the transition zone. Comparatively, for a soil subgrade under the transition zone, our results indicate that graded gravel + 5% cement is still the best filling material, while the other two less stiffer filling materials would result in considerable fluctuations to the roadbed surface.