| With the development of high-speed railway in our country to high altitude and high latitude,the railway roadbed stability is affected by freezing and thawing cycle and train load in seasonal frozen soil.Therefore,based on the engineering background of CRTSIII plate-type ballastless track subgrade at Limin tunnel entrance of the passenger dedicated line from Harbin to Mudanjiang,this paper studies the stability of CRTSIII plate-type ballastless track subgrade in the seasonal freezing area under train load through field monitoring,data processing,theoretical analysis,numerical simulation and other methods.The results of the research can provide some reference for safe operation of the dedicated railway line in Harbin and the design,construction and maintenance of the high-speed railway roadbed in other seasally frozen soil areas in our country.The main work and research achievements are as follows:(1)Through field investigation,data statistics and processing,the monitoring data of soil temperature,moisture content and displacement of existing monitoring points near the subgrade at the entrance of Limin Tunnel were analyzed.The results showed that the variation trend of soil temperature and atmospheric temperature was basically consistent,but the soil temperature was small and the variation range was low,and the average lag of the atmospheric temperature was 6-9 days.In winter,soil moisture content was low and stable,while in spring and autumn,soil moisture content fluctuated obviously.The displacement changes can be divided into four stages: the early stage of frost heave,the rapid development stage of frost heave,the relatively stable stage of frost heave and the fluctuation stage of thaw and subsidence,among which the rapid development of frost heave and the fluctuation stage of thaw and subsidence are the most obvious.(2)The sinusoidal function T=6.137+14.482*sin[2π/365(T-39.220)] fitted with temperature monitoring data was used as the upper boundary condition of the model temperature field analysis.The temperature field distribution and variation law of CRTSIII slatted ballastless track subgrade in the seasonal freezing area were calculated and analyzed by ANSYS APDL,and the results were obtained: The time-history curve of soil freezing showed "unidirectional freezing and bidirectional melting",and the maximum freezing depth was 1.61 m at the end of February.The structure of the track plate changes from "cold inside and cold outside" to "cold inside and hot outside" in the freezing period,while "cold inside and hot outside" in the melting period.(3)Through indirect thermodynamic coupling,temperature was converted into load and the distribution and variation of subgrade displacement field and stress field were calculated and analyzed.It was concluded that the vertical displacement time-history curves at different positions of subgrade showed a trend of first increasing and then decreasing,and the thawing rate was greater than the freezing rate.The maximum frost heave and settlement at No.4monitoring point were 3.1mm and 1.3mm respectively.According to the analysis of subgrade thermal stability,the thermal stability index of the model is 1.018-1.027,which belongs to the thermal stability of excessive type II.It is considered that the general human activities will have a small impact on the stability of subgrade.(4)The dynamic stability of subgrade in freezing period and melting period under the load of single and double track trains is calculated and analyzed by transient dynamics method.The maximum vertical displacement,namely the elastic deformation,produced by the train under load is-1.263 mm,and the additional settlement deformation produced by the train under long-term and repeated load in the 30 th year is 1.708 mm,which can meet the requirements of dynamic stability of high-speed railway subgrade. |
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