Study On Dynamic Response Characteristics Of Pile-Board Structure Of Low Embankment In High-Speed Railway

With the increasing speed of high-speed trains, the dynamic stability of low embankments also have higher requirements. To fully understand the dynamic response of low embankments is the need of high-speed railway subgrade design and guaranteeing the safety and efficiency of railway transportation. The indoor dynamic test, the dynamic response test and theoretical analysis are the primary means to study the dynamic response of subgrade. Due to the impact of test equipment, size effect and so on, the indoor test is difficult to ensure that the physical parameters satisfy the similarity theory, in situ dynamic test has the unique superiority in the study of different subgrade structure vibration response and deformation characteristics. The paper took dynamic response characteristics of pile-board structure of low embankment in beijing-shanghai high-speed railway as the research object, analyzed the technical characteristics of Southwest Jiaotong University DTS-1site dynamic test system, used DTS-1site dynamic test system to make dynamic sweep test and cyclic loading test to beijing-shanghai pile-board structure of low embankment, studied on the transient vibration response and long-term dynamic stability, combined with numerical methods to analyze the dynamic response characteristics. The main study results are as follows:First, the paper collected data at home and abroad, researched the existing in situ test system with the ability to work, summarized the corresponding technical problems of site dynamic test in high-speed operating conditions, analyzed broadband cascade load technology of multiple Indicator frequency amplitude regulation of Southwest Jiaotong University DTS-1site dynamic test system, and combined with engineering application to make its stability analysis.Second, aim at the pile-board structure supporting ballastless track of typical low embankment subgrade section, the main feature of the site was that between the pile-board structure and the ballastless track plate it filled a layer1.47m thick of coarse particle soil base bed, formed a pile-board structure-coarse particle sandwich-ballastless track plate the overall structure system, used DTS-1site dynamic test system to make dynamic sweep and cyclic loading test to the section. The sweep excitation vibration test results showed that, when the DTS-1site dynamic test system excitation vibration frequency gradually increases from5.0Hz to25.0Hz,the acceleration, velocity, dynamic soil pressure and dynamic displacement of dynamic impact parameters of the pile-board structure of low embankment increases gradually, each dynamic impact parameters and the excitation vibration frequency is approximately exponential function relationship, especially the unit amplitude of the pile-board structure of low embankment surface show the basic law of gradually increasing in frequency sweep excitation vibration frequency. In the range of excitation vibration frequency, peak has not appeared in both each dynamic impact parameters and unit amplitude, comprehensive results show that the site of the pile-board structure of low embankment does not produce resonance, at the same time it shows that the self vibration fundamental frequency of the site of pile board structure of low embankment is greater than25Hz,but the subgrade dynamic stiffness decreases with excitation vibration frequency increasing, the excitation vibration frequency can basically remain stable after reaching17Hz.The cyclic loading tests found that under the condition of the excitation vibration frequency of20.0Hz,the dynamic response of the measuring point fluctuate up and down more obviously in the excitation range of0～700,000times, the dynamic response of the measuring point of pile-board structure of low embankment is basically stable after cyclic loading700,000times, pile-board rigid foundation structure of the typical section of low embankment subgrade surface dynamic stiffness basically remained stable after cyclic loading700,000times.At last, the paper constructed a three-dimensional dynamic numerical calculation model of excitation vibration and pile-board structure of low embankment, studied the dynamic response and its regularities of distribution of pile-board structure of low embankment under the action of frequency varying disturbances, and the results were compared with the field test. The results show that, as the depth of embankment increases, acceleration and dynamic soil pressure of dynamic impact parameters decay gradually,, along the embankment longitudinal its trend is the "inverted triangle" distribution. Under the effect of excitation vibration frequency of20.0Hz, the dynamic stress of pile-board structure of low embankment decay about70% when it transfers to the ground. Under different excitation vibration frequency, in regard to vibration acceleration, vertical vibration velocity, dynamic displacement and dynamic soil pressure of pile-board structure of low embankment which are obtained by numerical calculation, the calculation value and the distribution are consistent with the site sweep test result.