Vibration Analysis And Engineering Applications Of Three-Dimensional High-Speed Train-Ballasted Track-Subgrade Coupling System

High speed railway has become an important symbol of China’s scientific and technological innovation and comprehensive national strength,and its vibration has been widely concerned by scholars worldwide.However,the existing research studies barely consider the coupling interactions of the train-track-subgrade system and the dynamic characteristics of foundation soils in detail.The tempro-spatial interactions among high-speed train,ballasted track and the composite subgrade（including the top and bottom embankment layers and the engineered and natural subgrade layers）is complicated in nature.Ignoring or decoupling such interactions would affect not only the operation safety and riding comfort of high-speed train,but also the long-term service performance of ballasted track.With the increasingly frequent occurrences of global warming and extreme climate disasters,high-speed railway lines have been increasingly exposed to moisture-related damages in flooding seasons.Ballasted trackbed and subgrade soils may form localized transient saturated zones under extreme precipitation conditions.It is thus necessary to consider the saturated state under such specific conditions and assess the consequences on the vibration responses of the coupling system and the operation safety of high-speed train.To address the above shortcomings,this thesis research study was conducted by integrating the theories and methods of multi-body dynamics,the finite element method（FEM）,the mechanics of elasticity,and the Biot dynamic consolidation model The numerical model was established for analyzing the vibration responses of the three-dimensional（3D）coupling system of the high-speed train-ballasted track-elasticor saturated porous media subgrade.As subsequent engineering applications,the case studies of the established numerical model were conducted on the commonly-observed rail fastener failure.The major research tasks and corresponding conclusions drawn are listed as follows.（1）By establishing the 3D refined models of the high-speed train,rail beams,sleepers,the ballast and composite subgrade layers,the energy equation of the 3D train-ballasted track-elastic subgrade coupling system was derived.Based on the principles of conservation of the total potential energy of the dynamic elastic system and the"seat in order"rule of forming system matrices,the global stiffness matrix,the global mass matrix,and the global damping matrix of the coupling system was formed,and the 3D viscoelastic boundaries were used to constrain the system.The dynamic equation of the coupling system was derived,solved by the Wilson-θtime integration method,and implemented by the commercial MATLAB^?software program.Accordingly,the developed model was verified by the field measured data.（2）The parametric sensitivity study of the main model parameters such as the running speed and the resilient modulus of the top embankment layer was performed by using the developed 3D numerical model of the coupling system.The calculation results show that the developed model can accurately predict the dynamic responses and related variation laws of each structural layer of the coupling system.In addition,the model was extended to the field maintenance practices of high-speed ballasted railway track.The influences of different patterns and quantities of typical rail fastener failures on the vibration responses of the 3D coupling system were simulated and analyzed,the running stability and safety indices of the high-speed train were calculated and assessed,and the corresponding maintenance countermeasures were recommended.（3）Based on the Biot’s dynamic consolidation theory and the FEManalysis,the 3D finite element based kinematic equation was obtained within the framework of solid displacement-pore fluid relative displacement（i.e.u-w）format of saturated porous elastic soil.In combination with the above-established 3D coupling model,the kinematic equation of the three-dimensional train-ballasted track-saturated subgrade coupling system was constructed by fully considering the interactions between the ballast layer and the saturated composite subgrade.By downgrading the saturated porous elastic subgrade model to the elastic subgrade model and utilizing the field measured data,the accuracy of the established 3D coupling model for analyzing vibration responseswas verified accordingly.（4）The developed 3D model of the train-ballasted track-saturated subgrade coupling system can predict the dynamic responses of each structural layer of the system,and can also obtain the variations of excess pore water pressure in the subgrade layers under the application of moving train loading.On this basis,the parametric sensitivity analysis of train speed,coefficient of saturated permeability,and the coupling stiffness of the ballast and saturated subgrade layers was carried out,and the order of relative influence was listed descendingly as follows:coefficient of saturated permeability>running speed>the coupling stiffness of the ballast and saturated subgrade layers.The research findings of this thesis study could potentially provide theoretical basis and technical guifance for vibration analysis,safe operation,and effective maintenance of 3D high-speed train-ballasted track-elastic/saturated subgrade coupling system.