| Crushed stone ballast bed is the basic structure of the ballasted track.Due to its granular properties,periodical maintenance works such as tamping and dynamic stabilizing are required in order to maintain track regularities in accordance with the specification,meanwhile,to improve its compactness and elasticity.The emergence of large-scale maintenance machine has greatly improved the efficiency of the construction and maintenance of ballasted tracks.Few research works have conducted on the technical operating parameters and working procedures of large-scale maintenance machine,result in the lack of sufficinet theoretical guidance in practice.The influence of the impact force of tamping pick on the deterioration of ballast is still unclear.What’s worse,it happens in China that after the work of large-scale maintenance machine,ballasted track has faced some problems,such as poor status of ballast bed,rapid deterioration of track geometry and so on.Therefore,it is of great significance to study the effect of maintenance works by large-scale machine on the qualities of ballast bed and the characteristics of ballast deformation,so that it can provide guidance for effective maintenance work.In this paper,the influence mechanism of large-machine combined operation mode on the state of the gravel ballast bed was systematically studied by a combination of theoretical research,numerical simulation and field tests.The findings of this study can provide valuable suggestions to the development of maintenance strategy based on the actual condition of the ballast bed.The main works of this paper are as follows:(1)A coupling model of large-scale maintenance machine-ballast bed based on discrete element theory was established,in which the ballast model was established based on the real ballast contour,and the models of sleeper and tamping device were imported in the form of 3-D geometry model.The tamping and dynamic stabilization process was simulated based on the basic operating principle of the DWL-48-type continuous tamping and stable vehicle.The reliability of the model was verified by comparing the simulation results with the results obtained from laboratory ballast box test introduced in the existing literature.(2)Through simulation analysis,the dynamic behaviors of the ballast under tamping and dynamic stabilizing were analyzed,including the state of motion and the change of compactness.And the mechanism of the effect of tamping and dynamic stabilizing on the ballast bed was studied.Furthermore,the influence of various operation paramaters on the mechanical qualities of ballasted bed was analyzed,including the track lift,tamping depth,clamping time,tamping mode in tamping operation and down force,and excitation frequency in stabilizing operation.Based on the analysis,the optimized values of those parameters were proposed.(3)Through theoretical simulation,this study obtained the effect of the combination of tamping and stabilizing operations and the number of operations on the mechanical properties of the ballast bed such as compactness and contact state.Through field tests,this study obtained the influence of the combination of tamping and stabilizing operations and the number of operations on the static mechanical parameters of the ballast bed such as lateral resistance.According to the characteristics of the newly built railway and the existing railway,suggestions were proposed respectively to optimize the process of the tamping and stabilizing combined operation.(4)The ballast breakage and the change of the gradation were studied by means of field tests.By analyzing the particle size distribution by mass under different tamping operation cycles,the influence of large-machine tamping operation on ballast deterioration was obtained. |
