| Railway is an important infrastructure in our country and a land public transport tool which is suitable for our national conditions.The railway network occupies a huge proportion in the national transport system,which plays an important role in promoting the comprehensive,coordinated and sustainable development of our country’s economy and society.As a traditional track structure,ballast track has the advantages of low construction cost,short construction period,high automation,mechanized maintenance efficiency and short maintenance time.In China,the ballast track is still used in special sections such as large bridges and elevated stations,but the instability of ballast beds on bridges are becoming increasingly prominent and urgent to be solved.In this paper,a great deal of work has been done to study the stability of ballast beds on bridges.The main contents and results are as follows:（1）By sampling the special ballasts,the method of obtaining and reconstructing the two dimensional profile of ballast is put forward based on the image processing technology and statistical law,which can generate the ballast profile in large batch according to the required size in practical engineering need.（2）Through the classification of the material parameters required for the discrete element model of ballast beds on bridges,the intrinsic parameters are directly obtained in laboratory tests,the contact parameters are obtained by combining the laboratory tests and simulative calibrations,the dynamic calibration idea of the discrete element model is put forward.Finally,all parameters needed for discrete element numerical simulation can be determined by two or more times calibrations.The ballast intrinsic parameters determined in this paper are as follows:the Poisson’s ratio is 0.25,the density is 2700kg/m3 and the young’s modulus is 2.5×1010Pa;The sleeper intrinsic parameters:the Poisson’s ratio is 0.25,the density is 2700kg/m3,the young’s modulus is 3.6×1010Pa;The ballast-ballast contact parameters:the collision recovery coefficient is 0.6,the static friction coefficient is 0.86,and the rolling friction coefficient is 0.03;The ballast-sleeper contact parameter:the collision recovery coefficient is 0.6,the static friction coefficient is 0.86,and the rolling friction coefficient is 0.03.（3）Based on the qualitative and quantitative analysis of the common troubles on the ballast beds on the bridges,the flow of ballast particles on the bridge,the change of the sleeper displacement,the change of the ballast-ballast contact number and the ballast-sleeper contact number,the change of the transverse longitudinal resistance,the stability of the ballast have been analyzed through discrete element numerical simulations under three actions of specific and common working conditions.The following suggestions are hereby proposed for design and construction,operation and maintenance:（1）The particularity of ballasted track on the bridge should be specifically optimized to enhance the stability of ballast bed during the design and construction phase;（2）In operation management,the relationship between traffic volume,density and axle load should be taken into account,and the volume and density of trains on ballasted track lines should be controlled scientifically and strictly.（3）In maintenance,a comprehensive survey of the running conditions of the train on the ballast track line should be done first,then a scientific and reasonable maintenance plan should be made according to the actual situation.The blind and frequent manual tamping can easily destroy the stability of ballast beds on bridges. |
