Study On The Dynamic Response Of Loess Railway Embankment Under Low Frequency Vibration Of Train

Railway transportation plays an important role in Chinese transportation industry because of its large volume,high safety and low environmental pollution.With the continuous implementation of the “National Medium and Long-Term Railway Network Plan(2016-2030)” and the development of “Shaving the mountains and building the city” projects in Yan’an city and Lanzhou city,the railway construction in loess area has a broad development prospect.However,the deformation and strength deterioration of railway embankment and environmental vibration in the loess area are also prominent,which seriously threaten the operation of railway trains.In view of this,some research works have been carried out,funded by the research project of “Study on filling and reinforcement technology of railway subgrade with large thickness filling in collapsible loess area”.The dynamic characteristics of unsaturated compacted loess and the dynamic response of loess railway embankment under low-frequency vibration of train were studied through experiment,theoretical analysis and numerical calculation.The main research contents and achievements are as follows:(1)The influences of confining pressure and loading control methods to the dynamic stress-strain relationship of compacted loess were studied by dynamic triaxial test.The results indicate that the dynamic stress-strain relationship of compacted loess accords with the hyperbolic model.The loading control method does not change the type of compacted loess backbone curve,but affect the value of the fitted parameters.(2)The dynamic coupling numerical model of the loess railway embankment,ballast-road embankment-foundation,was established based on the commercial software ABAQUS.The fixed boundary,viscoelastic boundary and infinite element boundary were compared and analyzed.The viscoelastic boundary is preferred as the boundary conditions of the numerical model in the present study.The ABAQUS software was redeveloped based on the FORTRAN language to realize the movement of the train load in the orbital direction.The influence of the number of vehicle groups to the dynamic stress and dynamic displacement amplitude of the embankment was analyzed.The three-car model was chosen as the train load model.(3)The distributions of dynamic stress,dynamic displacement,vibration velocity and acceleration response of various structural layers of were analyzed with axle weight 25 t and driving speed 120km/h.If the depth where the dynamic response attenuates to 20% of which on the surface of the embankment is taken as the influence depth of vertical dynamic stress,dynamic displacement,acceleration and vibration speed,the relationship of influence depth is: dynamic displacement > dynamic stress > vibration speed > acceleration.(4)The influence of train axle weight,speed and embankment filling height to the dynamic response of the loess railway embankment was analyzed.The results show that the axle load,speed and embankment height have little influence on the basic distribution characteristics of the dynamic response of each structural layer,but it will significantly affect its amplitude.In the range of bed,the effect of axle load on vertical dynamic stress and dynamic displacement is the most significant;the impact of speed on vertical acceleration and vibration speed is the most significant;the embankment filling height affects vertical dynamic displacement in a certain degree of.