Morphology Characterization Research Of Ballast And It’s Application In Discrete Element Model

Along with the extension of China’s high-speed railway development strategy,ballasted track structure is inevitably adopted in some areas.Considering the series of problems existing in the ballasted track under high-speed cyclic dynamic load,relevant technical analyses are urgently needed.The introduction of the discrete element method(DEM)effectively solves the shortcomings of the continuum-based method in analyzing railway ballast.However,the application of this approach to modeling ballast aggregates still has limited success.One of the major reasons is because the morphology of ballast aggregates in the numerical model are not related to the actual model in numerical form which leads to the results obtained by numerical analysis are not nuanced.In order to more accurately simulate the problems existing in the high-speed railway ballasted track,how to connect the numerical model to actual situation becomes the focus of this paper.For this purpose,the shape,angularity and texture of different sizes of ballast aggregates were firstly quantified.The shape of the aggregates was quantified using the flat-and-elongated ratio(FER).A separation method that separates the angularity and texture within aggregate images was proposed to accurately characterize the angularity.A modified angularity index(AI)and a proposed texture index(TI)were then presented.The FER,AI and TI values of different sizes of ballast aggregates were extracted,and their statistical distributions were studied.The uncompacted void contents of the different type rock aggregates in loose condition were used to validate the use of the presented AI and TI.The quantitative results provide the morphological representation of the actual ballast aggregates for the convenience of the study of particle generation in DEM model.Secondly,to generate the real ballast clump model in Particle Flow Code 3D(PFC3D),three-dimensional photo-reconstruction methods based on Structure from Motion and MultiView-Stereo techniques was introduced.A DEM particle generation method is then proposed to correlate the morphological characteristics of ballast aggregats in DEM with actual ballast aggregates.This method consists of the following steps:(1)quantify the morphological characteristics of the ballast aggregate to get the actual morphological numerical distribution;(2)generate the clump templates of the typical ballast particles in PFC,selected from the superfine ballast sample;(3)achieve the mass percents of the morphological numerical distributions by controlling the generated volume fractions of every ballast particle.This method can be used to correlate the morphological characteristics of the ballast aggregates generated in the DEM program with the actual ballast aggregates in the numerical form and hence provides a better solution to analysis the high-speed railway ballasted track problem.Thirdly,in order to make DEM simulation results correspond to actual mechanical behavior,the calibration of the model micro-parameters was carried out by using the previous research results.Meanwhile,a direct shear test device was desined and a direct shear numerical model that related to the actual test for the analysis of high-speed railway ballast was build.By comparing the numerical simulation results with the actual measured results,the parameters were futher validated.The meso-mechanical behaviors of the high-speed railway ballast in direct shear test was finally analyzed so that the direct shear mechanical behavior of the high-speed railway ballast is revealed in detail.