Theoretical And Field Test Analysis Of High-speed Train And Slab Track Coupling Interaction

With the fast development of high-speed railway in China, slab ballastless track is being widely applied due to its steadiness, smoothness, and low maintenance. However, as trains run faster, mild unevenness of the track (roadbed settlement, track surface irregularity, and stiffness unevenness) may all lead to great vibration response. which is tied up with train safety and passenger comfort. Vehicle-track dynamics, therefore, is an important subject of research.Through the Vehicle-Track-Subgrade Coupling Model and the results from a field test conducted on the Beijing-Tianjin Intercity Passenger Line, this paper is a systematic analysis of the vibration response propagation characteristics of the track structure during train operation and the influence of subgrade settlement upon train-track dynamic response. From the analysis, a series of control standards for track subgrade settlement was drawn. The main objects of the research include:The necessity of dynamics research on track structure is expounded in light of the issues of train operation safety and the influence on the surrounding environment. The literature from home and abroad on subgrade vibration induced by high-speed trains was summarized in terms of analytic derivation, numerical simulation, field tests, and model tests.The importance of coupling calculation of Vehicle-Track Model is established. By establishing the vibration differential equations of the subsystems of the train and track structure and adopting the wheel-rail linear contact premise, the two subsystems are coupled into a whole time-variant system. Newmark-beta's numerical method was adopted. Tricky problems during model calculation were raised and discussed, which include how to eliminate initial vibration responses of the train-track structure and how to ascertain the mode numbers of rail and discrete slabs.The field test conducted by the Geotechnical Institute of Zhejiang University on the Beijing-Tianjin Intercity Passenger Line during its trial operation was reported. The test includes track and roadbed vibration as well as the long-term settlement development of the subgrade during trial operation. The test results show that compared with ballasted track, ballastless track gives smaller structural vibration responses; as the increase of train speed, track responses enlarge accordingly; vibration propagates and dissipates rapidly in the track structure:the track shoulder four meters away from the track center has a vibration response peak value 8% that of the concrete base and the roadbed under the high embankment has a vibration response 2% that of the concrete base.The basic characteristics of vehicle-track coupling vibration response were analyzed and the effects of track surface irregularity distribution upon vehicle-track vibration were calculated. To verify the validity of the model, we simplified the model to the classic moving suspend masses over a simple supported beam model and floating slab track model and compared the results with those from other researchers' studies. The results coincide so well. In the analysis with moving suspend masses over a simple supported beam model, the importance of mass-beam coupling analysis was established through the analysis of the components of moment at the center of beam (induced by dynamic contact force and by inertial force of beam's distributed mass). In the analysis with floating slab track model, we discussed and proposed proper approaches to the problems of initial vibration and the assignment of rail and slab mode numbers.Under the chronic cyclic loading of trains, the track roadbed is prone to settlement and deformation, which leads to various irregularity distributions in the track structure. On the basis of vehicle-track coupling analysis model, we introduced the subgrade settlement premise and calculated the influences of settlement distribution lengths, settlement depths, and train speeds upon vehicle-track vibration response amplification. After the examination of different conditions and in light of the safety and comfort requirements for train operation, track subgrade settlement control standards under various train speeds were proposed.For ease of use, a High-Speed Railway Slab Track Dynamic Analysis Software was programmed using the GUI function of Matlab. The software has a simple and clear user interface, allowing automatic parameter loading using files or train-model data packages. The result output interface can display important indexes of vehicle-track dynamic responses and automatically save all the calculation results for future checking. There are also interfaces for different forms of track structure (ballasted track, track over bridge, etc.).The theoretical calculation and field test analysis in this study holds great implications for the prediction assessment of high-speed-train induced vibration response of slab track structure as well as the establishment of track subgrade settlement standards.