Study On Dynamic Characteristics Of Crts â…¢ Slab Track-Subgrade Under Impact Load

At present, the development of Chinese high-speed railway has entered the new stage of long-term safe and stable operations from the stage of large-scale constructions. How to achieve such long-term high security and stability of the operation has enormous challenges. Because the track structure is in complex service environment, and under the action of dynamic load of high speed train, the evolution of basic structural properties is inevitable, such as rail joint weld irregularity, uneven subgrade settlement of the ballastless track which causing whole dynamic characteristics of track structure and service performance changes. So it has strong theoretical significance and engineering application background to carry out research on dynamic characteristics and influence of impact load on dynamic response of the system. This paper use the wheel-drop test and finite element method to study the dynamic characteristics of ballastless track-subgrade under the impact load, mainly include the following contents and conclusions:A full-scale model experiment of wheel-drop impact under different wheel-drop height and the loading cross section location was performed on a typical CRTS III ballastless track-subgrade system. Vibration transmission law of foundation structure and the dynamical stresses distributions of overall CRTS III track-subgrade under wheel-drop impact loads are systematically analyzed with the help of three-dimensional dynamical analysis model, the result shows that ballastless track has good damping capacity and load diffusion. The peak stress distribution of track structure along lateral direction has a hump-shape in general and submits to normal one overall along longitudinal direction. The attenuation velocity of subgrade dynamic stress at different depths and different lateral positions are different. However, wheel-drop height and loading section position has little effect on distributions of the peak stresses, which just influence amplitude. Due to the weak constraint of the end of the slab, the stress concentration at the end of the track slab.The vehicle-CRTS III slab ballastless track-subgrade system vertical coupling dynamic model is established and the accuracy of the model is proved, which is used to compare the dynamic responses of different kinds of rail weld irregularities on the system. The result shows that:the rail weld makes the dynamic performances of the vehicle-track and subgrade system changed in different degrees, it has a great influence on the wheel and rail vibration was caused because they directly contacted with the irregularity. Different forms of weld irregularities had different influence on the system, the influence of the concave and convex weld irregularities on the dynamic characteristics are relatively close. After concave weld uneven stacked a short wave irregularity, the dynamic characteristics of the system increase significantly. With the established model, the dynamic responses of slab ballastless track-subgrade system are studied under the combined action of gravity load、certain uneven settlement load of subgrade. The influence laws of dynamic response by speed, wavelength and wave-depth are contrasted. It shows that, the upper layers of slab track structure deform accordingly with the subgrade settlement under gravity, gaps will occur when the uneven settlement is serious, and cause inter layer collisions under high speed railway conditions. The uneven settlement makes little difference on riding safety, but has a great influence on running comfort. The increase of the speed will increase the track structure response. Influence of different amplitudes or wavelengths of the uneven settlement have to do with whether the contact underneath support layer is lost and whether to cause inter layer collisions after contact loss. The dynamic responses of track-subgrade system is most acute when the wavelength is 20m, wave-depth is 20mm, all of which should be paid more attention.