Study On Dynamic Response And Its Influencing Factors Of Improved Soft Soil Subgrade Under Moving Loads

China is a vast country with complex and diverse soil.A large number of soft soils are distributed in coastal areas and downstream areas of rivers,which have high water content,low strength,poor permeability and low shear strength.In the process of railway construction,it is inevitable to encounter this kind of soil frequently.Under the action of moving train load,the subgrade in soft soil area will sink seriously,which will lead to poor track operation and seriously affect the safety and comfort of railway operation.In order to reduce the settlement and damage of subgrade caused by train operation in soft soil environment,it is necessary to analyze the vibration characteristics of soft soil subgrade under moving train load accurately,and then put forward reliable control methods.Therefore,on the basis of previous studies,this paper uses the combination of theoretical analysis and numerical simulation to study the dynamic response and influencing factors of soft soil subgrade under moving train load.The main research contents are as follows:(1)According to the real operating environment of railway subgrade,based on previous studies,the dynamic coupling model of train-irregular track-subgrade-soft soil foundation system is improved through Fourier transform and dynamic stiffness matrix method.The model is compared and verified with field measured data,and then the dynamic interaction between the train and the track is analyzed,and the dynamic wheel-rail force acting on the track structure is output as the input value of the dynamic wheel-rail contact force of the numerical model.(2)The theoretical model is used to study the dynamic response and vertical stress attenuation of improved soft soil subgrade under different influence factors.The research results show that the stress response caused by axle load is significantly greater than that caused by dynamic load,but the subgrade stress and displacement caused by dynamic load are very sensitive to the changes of track irregularity parameters and can not be ignored.Under the dynamic action,the smaller the irregularity wavelength,the greater the dynamic response of subgrade.When λ = 2m,the corresponding maximum dynamic stress amplitude of subgrade is about 2.9kPa,and the corresponding maximum dynamic displacement amplitude is about 0.039 mm.The dynamic response distribution of train wheelset is directly related,and the influence range is about 30 m,which is twice the train length.The dynamic stress gradually attenuates with the increase of depth,and the attenuation amplitude is the largest in the subgrade layer.The subgrade structure layer is very important to weaken the dynamic response of subgrade.With the increase of vehicle speed,the effect is more obvious.In engineering application,the reasonable design value of thickness and modulus should consider the technical and economic factors,which is of great significance to improve the operation effect of railway in soft soil area.(3)The numerical model is established by PLAXIS 3D finite element software,and the dynamic response law of soft soil subgrade under moving train load is analyzed by combining theoretical model and numerical model.The results show that train speed and track irregularity wavelength have important influence on the dynamic response of soft soil subgrade.In the two models,changing the structural properties of the improved layer has the same effect on the dynamic response of the top surface of the soft soil foundation.The semi analytical method and the semi analytical numerical combination method have a high degree of agreement,and they are both applicable and correct.