Adaptability of Heat-insulating Course to Prevention of Forst Heave of Unballasted Railway Track Subgrade in Seasonal Frozen Regions

In view of the engineering structure of unballasted track subgrade of dedicated passenger lines and the engineering characteristics of seasonal frozen soil in the northeast region of China,the indoor tests of the frost heave behaviors of coarse-grained soil were carried out.The results indicate as follows:Along with increasing of the fine grain content,the frost heave ratio and water bearing capacity of coarse grain soil increase correspondingly;when the content of fine grains of the size less than 0.075 mm reaches 5%out of the coase grain soil and after the test specimen is saturated and drained,the frost heave ratio of the test specimen is 1.31%.According to the geologic and climate conditions of the seasonal frozen regions along the Harbin-Qiqihar Dedicated Passenger Line,the two-dimensional finite element method was adopted to analyze the temperature fields of the existing and newly-built unballarted track subgrade with heat insulating courses for dedicated passenger railway lines across seasonal frost zones.The numerical results show as follows:For newly-built subgrades,the 10mmthick heat insulating course and insulating berm have good insulating effect,so frost prevention can be achieved;for existing subgrades,the heat insulating courses are laid on the top away from track pads and on the slopes and the heat-insulation effect is not obvious.