Study On Vibration Response And Vibration Isolation Of Train On Composite Foundation Based On 2.5-Dimensional Finite Element Method

In recent years,the density of China’s high-speed railway network is increasing,and the train speed is also increasing.At the same time,the environmental vibration caused by the operation of high-speed rail has also done harm to people’s normal production and life.It is necessary to conduct in-depth research on this.In the current numerical research methods,the two-dimensional finite element method can not consider the influence of train speed and load spatial distribution.The three-dimensional finite element method needs to establish a long model in the direction of train travel,and the calculation efficiency is relatively low.The 2.5D finite element method adopted in this paper can calculate the 3D spatial response only through a 2D profile by assuming that the material and geometric properties of the soil along the direction of the train are unchanged.It can not only take into account the calculation efficiency,but also consider the impact of vehicle speed,and has high accuracy.Firstly,the relevant 2.5D finite element / infinite element calculation program is compiled according to the 2.5D finite element theory,and the 2.5D numerical solution is compared with the analytical solution and the measured value to verify the correctness of the self-made 2.5D finite element program,and further analyze the response of homogeneous half space soil caused by train operation at different speeds.The results show that the calculation results of the 2.5D finite element /infinite element program established in this study are consistent with the existing analytical solutions and relevant measured values,and can accurately reflect the Mach effect when the load velocity exceeds the critical value,which has good applicability.Considering that the bearing capacity and stability of railway foundation are often improved by adding piles to the foundation to form pile-soil composite foundation in practical projects,the pile net composite foundation with pile soil appearing successively is equivalent to homogeneous soil layer by introducing the equivalent modulus method in foundation treatment,and a 2.5D train embankment composite foundation model is established.The numerical simulation results are compared with the measured values to verify the rationality of the equivalent treatment of composite foundation.Then,based on this model,the vibration response characteristics of embankment body and the propagation and attenuation law of vibration in the interior and surface of foundation soil are obtained.The effects of vehicle speed,embankment material modulus,subgrade bed stiffness,embankment height and pile-soil area replacement rate on the site vibration caused by the train are further analyzed.The results show that the train induced vibration can be greatly attenuated in the embankment,and the critical velocity of the train is mainly controlled by the Rayleigh wave velocity of the embankment material;The vibration of the middle area of the embankment slope under the train load is severe;Local vibration amplification will occur due to the reflection and superposition of waves during the transverse propagation of train vibration on the ground.Based on the established 2.5D finite element model of train embankment composite foundation,a filling ditch is added for vibration isolation research,and the vibration isolation research of the traditional single row filling ditch is extended to the new double row ditch,which provides a reference for the design of vibration isolation ditch in engineering.The results show that the dynamic response amplitude behind the filling ditch can be reduced,but the vibration amplification will occur in some areas before the filling ditch due to the superposition of waves;Compared with the single row ditch,the double row ditch can reduce the vibration amplification in front of the ditch and improve the vibration isolation effect behind the ditch;The spacing,material combination and depth combination of double drains are important parameters that affect the vibration isolation performance of double drains.