Dynamical Characteristic Of Ballastless Track On High Speed Railway And Its Application In Maintenance

Railway tracks have been improved to keep pace with the improvement of railway such as extension, speed-up and high density operation of vehicles. Ballastless track is widely used nowadays in high speed railways especially in China, Europe and Japan due to its many advantages for the constructions and operations of high speed railway lines infrastructures; such as its high stability and low maintenance.In this thesis, based on the comprehensive research of relative fields at China and abroad, an analytical model and calculation method for a slab track railway under high speed moving load was built up by means of the theoretical analysis and experimental study. The research work and main conclusions are divided into the following areas:1. Establishing the computing model and simulation method for dynamic analysis of slab track under high speed moving loadIn this thesis, the steady-state response of various models for railway track to a set of uniformly moving constant loads (train) have been investigated to reveal the factors which are of primary importance in the dynamics of high speed ballastless track railway and to compare different track models.Concerning the parametric analysis of the models, the main attention has been paid to the configuration of the ground sub-soil, damping in the ground, in the pads, and the effect of the spatially discontinuous rail-ground interaction that is caused by the sleepers.Based on the beam shell model on elastic foundation, a slab track simulation model was established. The dynamic characteristics of the slab track were analyzed. The rail was simulated by Euler beam. Bearing layers were simulated by elastic thin shell. The elasticity of the fastener, CA mortar and subgrade were simulated by spring combination. The model was actualized using FEM. A calculating program of the simulation method was coded and verified by some known results.The characteristics and rule of high speed ballastless track railway under dynamic loading were summarized and discussed.The dynamic responses of ballastless track under high speed moving load were given, and the effect of vehicle velocity on the track dynamic responses was studied. The results showed that the dynamic bending stress of CA mortar and dynamic stress of subgrade increases with the increase of vehicle velocity.Elastic drag experienced by a high speed train due to excitation of ground vibrations has been analyzed. It has been shown that the elastic drag can be comparable and can exceed the aerodynamic drag (starting from the velocities close to the Rayleigh wave velocity). Thus, the elastic drag is an important design criterion for high speed trains to be accounted for as a source of perceptible energy loss.2. Establishing the computing model and simulation method for the vertical forces and deformations rule due to irregularities on wheel/rail of slab track under high speed moving loadIn this thesis, the interaction between rail-wheel for high speed railway slab track with irregularities were modeled, calculated, simulated and researched in detail.Based on the vertical interaction relations, an integral FE model of slab track with a computing program was developed using the non-linear FEM. A comparison between site test results of Suining-Chongqing test line and theoretical calculated results was discussed, which primarily showed a significance correlation, proposing that the calculating method and simulation method can be considered correct and reasonable.3. Studying the effect of the stiffness and damping on the behavior of the slab track under high speed moving loadThe study of the effect of the stiffness and damping in the considered models has shown that, the subgrade stiffness mainly influences the acceleration of the base slab, but the degree is relatively small. Although the increase of the damping (in the subsoil, and in the pads) generally reduces the amplification of the track vibrations at the critical velocity, it leads also to a substantial increase of the elastic drag in the sub-critical case. That is why the increase in the damping can cost a perceptible energy loss, which is unfavorable for high speed transportation.4. Studying the effect of critical velocity of the train and sub-soil conditions on the behavior of the slab track under high speed moving loadThe investigation of the influence of ground stratification on the dynamic response of the railway track to a constant moving load has demonstrated that the soil stratification strongly affects the dynamic response of the railway track.The results showed that the critical velocity of the train that is conditioned by its dead weight (constant load) is approximately equal to the Rayleigh wave speed in the ground surrounding the railway track. This result is as valid for a homogeneous (embedded) track as for an inhomogeneous (conventional) track. The magnitude of the critical velocity depends mainly upon the physical properties and saturation of the sub-soil. If the ground is soft, the value of the critical velocity, varying from 150 to 300 km/h, is attainable by contemporary high speed trains. This implies that a careful study is necessary of what would happen if such a regime of motion were to occur.Variations in depth of the soil layers and in their physical properties can result in; shifting and introducing new critical velocities of the train; reducing or increasing the dynamic amplification of the track response; and scaling the spatial pattern of the rail response.5. Proposed an inspection and maintenance technique to be used for high speed slab track railway in ChinaIn this thesis, some inspections and maintenance techniques world wide existed and used were discussed. Based on these existed techniques and experts, the proposed method was advised to be implemented and used in Chinese high speed ballastless track railway systems, which might be helpful in the operation, management and rehabitation of the existing and the new PDLs high speed railway in China.