Research On Dynamic Characteristics And Cumulative Plastic Deformation Of High-speed Railway Foundation Filling Under Cyclic Dynamic Load

In recent years,high-speed railways have developed rapidly in my country due to their advantages such as speed,safety,efficiency,and environmental friendliness.At present,China's total high-speed railway operating mileage ranks first in the world.The subgrade directly subjected to the long-term effect of the dynamic cyclic train loads transmitted from the track structure,investigation of its dynamic behavior and plastic deformation characteristics under the dynamic train loads may provide ideas for the subgrade performance evaluation and settlement control.In this paper,based on the National Natural Science Foundation of China,the dynamic characteristics and cumulative plastic deformation of the graded broken stone filler under long-period cyclic dynamic loading were analyzed through the construction of element filler model,and combined with numerical analysis to determine the parameters of the cumulative plastic strain calculation model suitable for the filler.The main work and conclusions are as follows:(1)Designed and carried out the element filler model test.The geometric size of the element model is determined according to the transmission and attenuation range of the dynamic load.The side panels of the model box and the sandbag wall that allow lateral displacement are used to simulate the local element structure in the actual subgrade.In accordance with the requirements,the percentage of the granular group of the graded broken stone was designed and verified,and the degree of compaction was tested layer by layer to ensure that the filling quality of the fill model meets the requirements.The loading frequency was designed based on the actual train and subgrade dynamic response characteristics,and a total of 1.68 million sinusoidal cyclic dynamic loads were applied to the filler model.The dynamic response and deformation of the filler model during the loading process were tested using a self-made vertical deformation measuring device,dynamic measuring element and dial indicator.(2)Based on the test results of the model test,the development law of vertical cumulative plastic deformation with the load times is obtained;the influence of load level and loading frequency on dynamic stress,vibration acceleration,elastic deformation and cumulative plastic deformation is analyzed,and the dynamics are obtained.The response and deformation change with the depth of the roadbed.The results show:(1)With the increase of the load level,the vertical dynamic stress increases linearly,and the cumulative plastic deformation and vertical elastic deformation increase slightly in the beginning and then rapidly,and the vibration acceleration shows an overall increasing trend.(2)The dynamic stress and vertical elastic deformation show an overall attenuation trend along the depth of the roadbed.The depth range of 0.75 m below the top surface of the model is the main attenuation area of elastic deformation.The vertical cumulative plastic deformation mainly occurs in this area,and the lateral cumulative plastic deformation is along the road.The base depth does not change much.(3)The vibration acceleration increases with the increase of the loading frequency,and the vertical elastic deformation decreases accordingly.The higher the load level,the more obvious the change;the load level remains the same.The growth effect presented by the increase is not obvious.(3)Based on test results,the cumulative plastic strain calculation model that consider the effects of residual stress and lateral plastic strain was selected,combined with the threedimensional stress components and models of each soil layer calculated by the threedimensional finite element simulation calculation.The test results determine the calculation model parameters suitable for the graded broken stone filler,which can provide a basis for the prediction and analysis of the cumulative plastic deformation of the subgrade in the actual project.