Modeling Method And Dynamic Response Analysis Of Railway Subgrade Under Impact Load

Subgrade is an important part of railway lines.When special train transporting and operating,heavy haul train bumping,or hoisting equipment working,there can be great vertical impact loads acting on railway subgrade.During the loading process,the railway subgrade will vibrate and deform,causing coupled movement of the train and the related equipment on the rail to be disturbed.In order to study the dynamic response and variation law of railway subgrade during the process of impacting load,the subgrade was modeled,simulated and analyzed.According to the characteristics of impact load,combined with the finite element method and infinite element method and based on ABAQUS software,a reasonable and effective finite-element simulation model of subgrade was established with layered structure,elastic-plastic material and infinite boundary.On this basis,the dynamic response of subgrade model under impact load was studied,and the influence of foundation stiffness and load on the subgrade response were also analyzed.The bearing capacity under impact load of typical Grade I as well as Grade III and IV were discussed respectively.The requirements that the subgrade is supposed to meet for itself and the equipment on it to operate normally were analyzed,providing references for pre-judgment of load effect under different railway conditions.Based on the vibration response of the subgrade model,further simplification of the subgrade model was studied,which lays the foundation for subsequent subgrade research and the application of the subgrade model.The main results are as follows:(1)According to the characteristic of the impact load,based on the specification and practice of existing Grade I railway subgrade,the modeling method was studied.The 3D simulation model of subgrade with finite length was established through finite element software,and the correctness of model was verified by an example.(2)The dynamic responses of subgrade under impact load were calculated and analyzed,including vibration,deformation and the attenuation of dynamic stress,forming a comprehensive study on changing process and results of railway subgrade under impact load.(3)Considering the influences of different ground environment and load size,the response rules of subgrade to impact load under different line conditions were discussed.The effect of impact load was judged according to bearing capacity of each layer.(4)The subgrade models of Grade III and IV railways were established.The responses of low-grade railway subgrade to impact load were calculated,and the analyzing process whether the subgrade meets the requests of impact load was discussed.(5)Through the comparison of calculated results of different modeling methods,the conclusion that the plasticity of subgrade material has little influence on subgrade vibration was obtained,and the importance was analyzed of boundary processing in the calculation of vibration response.(6)The method of simplifying the model to spring-damping model according to the vibration of the finite-element subgrade model was proposed.The calculated stiffness and damping value are equivalent to the theoretical results through comparison,which proves the rationality of the calculation method.