Research On The Settlement Of Lanxin Railway Subgrade Under The Condition Of Train Speed Increase

With the rapid development of China's railway transportation,the speed of trains has greatly increased,bringing convenience to the people.However,the design standards of existing line's foundations are low and cannot meet the requirements of train speed increase.Long-term operation will cause the settlement of road foundations.Therefore,it is necessary to study the vibration response of the roadbed under the condition of train speed increase and predict the long-term settlement law of the roadbed.Based on the subgrade project of the Urumqi to Kuitun section of the Lanxin Railway,the paper understands that the dynamic load increases after the train speed increase,resulting in insufficient bearing capacity of the subgrade,which is the main reason for the settlement of the subgrade.Based on the subgrade project,the numerical simulation method is used to analyze the vibration response of the subgrade under the condition of train increase,and then the theoretical calculation method is used to predict the long-term settlement of the subgrade,and the control measures are proposed.As follows are the research contents and conclusions:(1)Refer to domestic and foreign research results on subgrade vibration response and long-term settlement,introduce related theories,and use the Urumqi to Kuitun section of the Lanxin Railway as the engineering background to analyze the basic situation of the project.It is concluded that train speed increase is the main cause of subgrade settlement factor.(2)A three-dimensional finite element model of the bed-subgrade-foundation was established through MIDAS/GTS/NX to simulate the loading effect of a moving train and use the finite element dynamic solution method for numerical calculation.The time-history curve of the dynamic displacement on the subgrade surface and the attenuation law of the dynamic displacement and dynamic stress in the depth direction are obtained.It is concluded that the dynamic displacement value does not meet the requirements of the specification when the train speed is 120 km/h.(3)Calculate the long-term settlement of the roadbed under the load of the train according to the layered sum method,and then convert the load at different train speeds into static loads.Use the numerical simulation to calculate the settlement of the roadbed.Through comparative analysis,it is found that the maximum settlement value of the numerical simulation is 39.42 mm,which is slightly larger than the theoretically calculated maximum settlement value of 37.85 mm,and the simulation result is closer to the actual monitoring value.(4)Aiming at the settlement of the Lanxin railway subgrade,the high-pressure jet grouting piles were used to strengthen the governance.Through a comparative analysis of nine working conditions,the optimal design parameters of the jet grouting piles were that the vertical tilt angle was 60o,the length of the pile was 8 m,and the distance between piles was 2m.After adopting this solution,under different train speeds,the dynamic displacement of the subgrade was reduced by 12-17%,and the settlement value of the subgrade was reduced by 15-18% compared with the original.The treatment effect was significant,which can meet the requirement of train speed increase to 140 km/h.