Study On Design Loads And Subgrade Settlement Limits Of Ballastless Track For 400 Km/h High-speed Railway

With the rapid development of high-speed railway,China has formed a relatively systematic technical standard system for high-speed railway with speed of 350 km/h and below,and accumulated rich experience in safe operation.The development of high-speed railway with speed of 400 km/h and above has become an important trend and strategic demand.In high-speed railway,ballastless track has become the main track form due to its outstanding advantages.After decades of rapid growth of railway,China has gradually mastered a complete set of technologies for ballastless track of 350 km/h high-speed railway,and independently developed a ballastless track structure with advanced technology and completely independent intellectual property rights.So far,for high-speed railway with the design speed of 400 km/h or higher,there has been no operational railway at home and abroad,and no corresponding standards for key design parameters of ballastless track.How to design ballastless track structure to ensure the safety and stability of high-speed running is a significant scientific and technological challenge.Therefore,focusing on the design load of ballastless track,uneven settlement of subgrade and other fators,this thesis carries out the dynamic analysis and research on the key design parameters of ballastless track of 400 km/h high-speed railway.The research results can provide important theoretical reference for the design and construction of400 km/h high-speed railway.The main research and its conclusions are as follows:(1)Considering the spatial nonlinear mapping relationship between subgrade settlement and track geometric state,a vehicle track system dynamic model reflecting the influence of subgrade settlement is established.Based on the plate–beam model on Winkler foundation,a Fourier series solution of relationship between spatial subgrade settlement and track geometry is proposed,characterized with fast iterative convergence,series convergence and acceptable accuracy.Compared with the traditional two-dimensional analytical model,the model can fully consider the difference of settlement spatial distribution,and can finely reflect the vertical deformation,transverse deformation,spatial interlayer unsupported area and its influence on the dynamic performance of vehicle–track system.Compared with the finite element numerical solution,the series solution has a clear expression,which can be more efficiently substituted into the vehicle–track coupling dynamic model for dynamic simulation analysis.(2)Based on the theoretical model of vehicle–track coupling dynamics,the study on the design load of ballastless track is performed.The determination of fatigue checking load of ballastless track structure follows the distribution law of wheel–rail force under random track irregularity excitation.According to the bearing characteristics of ballastless track with adverse wheel–rail impact caused by wheel flat and rail weld joint,the design load of ballastless track structure is analyzed.The results show that the transverse fatigue checking load in the current code has good adaptability to the ballastless track of 400 km/h high-speed railway,while the vertical fatigue checking load has poor adaptability.Considering the bearing characteristics of the main structure of ballastless track,it is suggested that the design load of 400 km/h highspeed railway should be taken according to the analysis results of fastener reaction force.The design load could follow the existing specifications,and the vertical and transverse design load coefficients should be 3.0 and 0.8 respectively.(3)Focusing on the problem of uneven settlement of subgrade of high-speed railway,the influence law of settlement on track geometric state and dynamic performance of vehicle–track coupling system is analyzed,and the limit of uneven settlement is studied.The results show that under the action of structural self weight,the influence laws of settlement parameters(wavelength,ampitude)on track deformation,deformation following,voids amplitude and voids area are different.The settlement within the wavelength of 12～20 m is more likely to lead to large-scale voids between track and subgrade.The settlement trough and boundary position are prone to void,and the voids is not completely evenly distributed along the transverse direction.Compared with the speed of 350 km/h and below,the settlement has a more significant impact on the acceleration of car body and the wheel-rail force,thus affecting the comfort and safety of vehicle operation at higher running speed.According to the influence law of geometric parameters of subgrade differential settlement on the dynamic performance of vehicle-track system,from the perspective of dynamics,it is suggested that the amplitude of subgrade differential settlement should not exceed 20 mm,and the existing specification limit of 15 mm is suitable for 400 km high-speed railway.(4)Aiming at the problems of angular,staggered and transverse differential subgrade settlement of line foundation,the limit of abrupt settlement is analyzed.The results show that the change of angular settlement parameters in the transition section has a significant effect on the vibration acceleration of the car body.The vertical acceleration of car body and the load reduction rate of wheel load increase obviously with the increase of stagger settlement amplitude.For the 400 km/h high-speed railway,it is suggested that the limited angular value should follow the existing specification value of 1 ‰,and the limited stagger value should follow the existing specification value of 5 mm.