Research On Freezing-Thawing Variation Of Seasonal Permafrost Subgrade Of High-Speed Railway

With the rapid development of the national high-speed railway,the requirements for the running smoothness and stability of the high-speed railway have been gradually improved.At present,one of the main problems restricting the development of high-speed railway in China is the frost damage of subgrade in seasonally frozen soil area,and scholars can not accurately grasp the laws of temperature field,water field and frost heaving in the process of freeze-thaw cycle of high-speed railway subgrade,which results in the failure to take effective prevention and control measures to completely solve the problem of frost damage.Therefore,it is necessary to study the freeze-thaw laws of the subgrade of high-speed railway in seasonal frozen soil area.Based on the engineering background of Harbin-Dalian high-speed railway freeze-thaw monitoring project,this paper studied the freeze-thaw laws of high-speed railway foundation in seasonally frozen soil area by the combination of theoretical analysis of freeze-thaw damage factors,comparison and analysis of monitoring data and numerical simulation.The main research results are as follows:（1）The geological and geomorphologic features,climatic conditions and hydrological characteristics along the Harbin and Dalian high-speed railway were investigated.Based on the results of previous studies,factors（moisture,temperature,load and soil properties）of Harbin and Dalian high-speed railway were analyzed and the mechanism of action of each factor was analyzed.（2）Based on the freeze-thaw monitoring project of Harbin and Dalian high-speed railway,the typical monitoring location and monitoring section are selected.Through comparison and analysis of on-site monitoring data,the variation rules of ground temperature,water content and frost heave amount at different locations and depths of subgrade in the freeze-thaw process are obtained.（3）Based on the temperature plate calculation principle of FLAC^3Dsoftware,the control equation of energy transfer and thermal coupling equation were determined.In this paper,the Mohr Coulomb model was used to evaluate the parameters of different soil properties in the model,and the thermo mechanical coupling model of Subgrade Frost heave was established.The comparison between the calculation results of the model and the analysis results of the monitoring data verified the authenticity of the temperature field,the change rule of the frost heave amount in the process of freeze-thaw and the reliability of the model.（4）Based on the analysis of the prevention and treatment measures of frost damage on the railway foundation in seasonal frozen soil area,the relevant Suggestions on the treatment of frost damage on the roadbed were given in combination with the treatment measures offreezing damage on the site of Harbin and Dalian high-speed railway and the research results of freezing and thawing rules.