Study On The Effect Of Loess Site Under The Load Of High-speed Train On Baji-Lanzhou Passenger Dedicated Line

Under the initiative of the Belt and the Road and basic construction of four-vertical-and-four-horizontal high speed railway network,a large number of high-speed railway networks have been built in Shanxi,Gansu,Ningxia and other regions of Loess Plateau.Meanwhile,because of the special properties of loess such as strong water sensitivity and high dynamic vulnerability and a lot of special landforms of the Loess Plateau such as slopes,tablelands,beams and hills,the Loess topography along the railway may be destabilized and damaged,as well as the subgrade settlement,under high speed train load,which will cause serious geological disasters and affect the normal and safe operation of high-speed train.Therefore,in this paper,the field geological survey is carried out,and the typical loess topography along the Baoji-Lanzhou passenger dedicated line is selected as the research object,that is,the stepped slope of loess in the embankment section and the Loess Plateau site under the viaduct.The acceleration time histories of different speed trains passing through these two test sections are recorded by field vibration test,and the test data are analyzed in time domain and frequency domain.And the corresponding model is established by using the finite element software to analyze the stability and the vibration characteristics of different slopes and loess tableland under the train load.At last,the change rule of acceleration vibration level with distance in each central frequency band is analyzed by using one third frequency range analysis,and the law is fitted and analyzed.The following research results are obtained:?1?The acceleration test of step slope of embankment section and Loess Plateau under viaduct along the Baoji-Lanzhou passenger dedicated line is carried out.In the time domain,a_max?the acceleration peak value?,VAL?vibration acceleration level?and K?kurtosis index?are used to analyze the influence of train speed and site topography on vibration propagation,as well as the operation characteristics of the train itself.In the frequency domain,Fourier spectrum,energy spectrum and one third octave band are used to analyze the vibration characteristics of different sites under different speed train loads,and the causes of vibration amplification are analyzed.?2?The acceleration time history curve at the first step of loess stepped slope of embankment section is analyzed by using Hilbert Huang transformation,which can be used to judge whether the train passes through the test section in the state of variable speed or uniform speed.The vibration characteristics of the Loess Plateau under the viaduct are analyzed by using the acceleration response spectrum.It is found that the predominant period of the site is about 0.025s.?3?By using the finite element numerical software ABAQUS and combining with the characteristics of the site,different forms of slope sites of the embankment section and different forms of loess tableland under the viaduct are established,and the stability of different forms of loess sites under the action of train load is analyzed.The possible locations of damage are described.The dynamic responses of different sites are analyzed,and the differences of vibration propagation between different types of slopes and different types of Loess Plateau sites are respectively compared.In addition,the influence of soil mechanical parameters on vibration propagation is also analyzed.?4?The relationship between acceleration level and distance in each central frequency band of loess stepped slope in embankment section and Loess Plateau under viaduct is analyzed by using one third frequency range transformation.The same change rule is classified,and the law of its change with distance is fitted.It is found that there is a great difference in the law of acceleration level changing with distance in each frequency band of the same site,and the change rule of acceleration level of each frequency band of loess stepped slope is quite different from that of Loess Plateau.