Dynamic Response Analysis Of High Speed Railway Ballast Track Subgrade In Deep Seasonal Frozen Region

At present,the dynamic response evaluation index of high-speed railway subgrade is single,the research content is not comprehensive,and most of them are concentrated in unfrozen region.In order to study the distribution characteristics,generation mechanism,propagation law of dynamic response of subgrade,this article takes the railway embankment in deep-season frozen region under the vibration load of high-speed trains as the main research object,comprehensively using a variety of research methods such as field monitoring,numerical simulation and theoretical analysis.The main research content and conclusions are as follows:Firstly,at the typical section of Harbin-Jiamusi high-speed railway,the field monitoring of vibration response of ballasted track subgrade during frozen and unfrozen periods was carried out.Based on the monitoring data,the characteristics of the time-history curve,the law of amplitude attenuation and the spectrum distribution characteristics of the vertical vibration acceleration at each measuring point were analyzed,and the influence of the speed and seasonal changes on the amplitude-frequency characteristics of the subgrade vibration response was studied.Secondly,based on the coupling dynamics theory,the vehicle-track-sleeper-track bed vertical coupling model with multi-section grouping is established in the finite element software using Python and then obtain the sleeper force when the train passes by.Later,the reliability of the model is verified by comparison with the field measurement data of the Qin-Shen high-speed railway.Thirdly,according to the relevant data,the unsteady temperature field finite element model considering the phase change is established for the railway subgrade in the deep seasonal frozen region.The temperature field simulation results show that: in the deep seasonal frozen region,the temperature field inside the subgrade changes with the alternation of four seasons,because of the difference of the heat transfer property of the soil,the temperature propagation in the subgrade has obvious hysteresis.According to the temperature field inside the subgrade and the freeze-thaw state,the subgrade in seasonally frozen region can be divided into normal period,frozen period and melting period.At last,the indirect coupling method of thermology and mechanics was used to study the transient dynamic problems under train load.According to the model,the influence of seasonal variation,train load type,train load amplitude,train speed on the distribution characteristics,attenuation law and amplitude frequency characteristics of subgrade dynamic response are analyzed,and the propagation law of each dynamic response are discussed,as well.The results show that the different mechanical properties of soil in different frozen period make the amplitude frequency characteristics of subgrade dynamic response different greatly;Compared with the single vehicle load,the dynamic response amplitude of the subgrade under the double vehicle load is increased,but the increase amplitude is quite different,especially in the surface layer of the subgrade;The vertical acceleration,velocity,displacement and other dynamic response indexes of subgrade are caused by different frequency components in the vibration wave,so there are obvious differences in the attenuation law in the process of transmission to the outside.The conclusion of this article can further deepen the understanding of the dynamic response of the high-speed railway subgrade in the seasonal frozen region.,and provide reference for the design and construction of railway subgrade in seasonal frozen region,traffic organization design,prediction and evaluation of site environmental vibration along railway and subway,as well as the development of accurate vibration reduction and isolation measures.