Dynamic Responese Test On Exsiting Railway And Study On Dynamic Action Characteristics Between Speed-Increase Trains And Subgrade In Soft Deposits

With the repid development of railway transportation in our country, many exsiting railways are in gread need of raising speed and reconstruction due to lacking transportation capacity. In soft soil area, lots of subgrade problems will be faced to increase the speed of exsiting railway ,such as large subgrade settlement, many railway bed diseases, and heavy differential settlement in the bridge-subgrade transition. Raising speed of exsiting railway will intensify the dynamic effect on subgrade under train loads, increase the pressure of subgrade and speed the accumulative deformation of subgrade. It results in damages to the track structure and stabilizaiton and safty of railway. Present methods of design on of exsiting line transform always set out in condition of static or pseudo-static analysis, ignoring the dynamic problems of subgrade relevant to line speed .In order to evaluate the influences on exsiting railway subgrade with line speed raised.This paper set out from dynamics with the raising speed and resconstruction of Shanghai Jin Shan exsiting railway as the base, using of the method of dynamic respones feild test and numerical simulation of finite element, and characterisitcs of dynamic effect between speed-increase trains and existing railway subgrade were studies in this paper. These research contents were done as fellows.(1) Based on the investigation results of current situation of exsiting railway and method of acceleration test, the scheme of feild test on the vibration of subgrade structure was designed. Acceleration tests on key position of traditional subgrade and bridge-subgrade transition were completed.Through analysis on test data, the regularity of subgrade acceleration spatial distribution and the characteristics in time domain and frequency domain were found,and acceleration esponse characterisitics of track and the surface of subgrade bed in the zone of bridge-subgrade transition were obtained.(2) On the basis of large-scale infinite element analysis platform of ABAQUS, dynamic analysis model of tranditional subgrade under the test conditions was build.using the test data of acceleration of surface of subgrade bed as system excitation to simulate the train loads, the dynamic responses of subgrade before raising the speed of line were obtain through numerical computation. In terms of acceleration,the result of test was in accord with theoretical result, and effectiveness of the proposed analysis model was validated.(3) According to the load vertical transfer pattern,two methods to simulate train loads were proposed in this paper: moving loads and dynamic loads function in time domain. Under the condition that the simulated result before raising speed was in accord with the measured value, the influences on dynamic response characterisics of tranditional subgrade due to raising the speed of trains were studied. The paper proposed two dynamic analysis indicators of the influential depth of dynamic stress and additional settlement under dynamic action,and summarized their characteristics changed with the growth of speed.(4) Three-dimensional dynamic analysis models of finite element of subgrade-feild and track-foundation in zoon of bridge-subgrade transition were bulid. Using the moving loads to simulate train loads,the impacts on dynamic stress and deformation of subgrade in zone of transition and the track vibration were studied and evaluated. The changes characterisics of track vibration in bridge-subgrade transition with longitudinal distance and differential settlement between bridge and subgrade changing was studied.