| In recent years,China’s high-speed railway has developed rapidly.Until now,the total mileage of high-speed railway operations in China has exceed 35,000 kilometers,and it is the country with the longest high-speed railway under construction and operation in the world.The newly built high-speed railways in China with a speed of 250km/h are mainly adopted by ballastless track structures,while with the accumulation of operating hours,the diseases,like arches and cracks,in ballastless track structures gradually appear.Besides,these diseases have gradually developed from sporadic occurrence to universal occurrence,which increases the workload of maintenance and repair,and also affects the comfort and safety of operation.However,the ballast structure can effectively avoid the above-mentioned diseases.In addition,except for the high-speed railways that have been reconstructed by the existing railways which nearly all use ballast track structures,in some special locations such as the elevated stations,large-scale departure stations,bridges,large-number turnouts,long-span bridges,etc.,the ballast track is employed,which is suitable and easy to maintain.And under the China Belt and Road Initiative strategy,the foreign high-speed railway lines are basically based on the ballast track.These factors make the research on mechanical characteristics and structure selection of ballast-track structure of high-speed railway have important research value and great engineering practice significance.In China,bridges account for a large proportion of high-speed railway infrastructure,and the bridge are rigid structures.According to the result of International Railway Union research,under high-speed operating conditions,the ballasts of the track on the bridge will be pulverized,the trackbed will be unstable and the ballast splash will occur.However,China lacks systematic research on the mechanical properties of the ballast track on bridges with a speed of 250km/h and above,and cannot scientifically guide the design and selection of the track structure.Therefore,it has seriously restricted the promotion and application of ballastless track in China high-speed railway.Based on this,this paper mainly studies the mutual dynamic characteristics and structure selection of ballast-track and bridge on high-speed railway bridge from the aspects of data investigation,finite element simulation,discrete element analysis,and field test,etc.The specific work is as follows:(1)Comprehensive analysis of the research status of the structural form and mechanical characteristic of ballast track at home and abroad,combined with the actuality of China high-speed railway project,initially proposed an optimization scheme suitable for the sleeper type and damping measures of the ballast track on the bridge.(2)A high-speed train-ballast track-bridge dynamics coupling analysis model is established.At the same time,the sleeper-trackbed interactional analysis model is established by the discrete element method,the corresponding model parameters are determined,and the reliability of the model is verified.(3)The coupled dynamic analysis model and the discrete element model are used to analyze the mechanical characteristic of the sleepers on the bridge.Computational analysis shows that dynamic characteristics of the ballast track structure on the bridge adopted four types of track structures,namely type III sleepers,wide sleepers,ladder-type sleepers,and frame type sleepers,can meet the existing evaluation standards;comparing the wide sleeper structure,the ladder-type sleeper,the frame type sleeper,and the traditional type III sleeper,it is found that the mechanical properties of the wide sleeper are superior,the mechanical properties of the type III sleeper are middle,and the other two are slightly worse.(4)The coupling analysis model and the discrete element model are applied to analyze the effect of different damping measures on the high-speed railway bridge.The results show that after adopting the above measures,the trackbed and bridge structure have obvious damping effect,and the indexes can meet the requirements of the code.(5)The site test of ordinary ballast track on the bridge,ballast track + extruded plate cushion,ballast track + polyurethane cushion,and ballast track + elastic sleeper is carried out to study the dynamic characteristics.The results show that setting sleeper pad and rubber pad significantly reduces structure dynamic characteristics under the high-speed railway load of trains,and can effectively reducing trackbed pressure stress,so as to reduce maintenance.(6)The excavation of the ballast on the bridge where the ballast track uses different ballast pads shows that the ballast has a good contact relationship with the ballast pad.Due to the geotextile on the side of the contact surface with the ballast of the polyurethane pad,the ballast indentation is not found;the indentation depth of the extruded sheet is mainly distributed in the range of 0-4mm.(7)An optimization scheme for ballasted track structures on high-speed railway bridges is proposed.The finite element and discrete element methods are used to analyze and verify the optimization schemes.Finally,suggestions for the selection of ballasted track structures on high-speed railway bridges are proposed. |
