Experimental Study On The Water-Heat-Vapor Effect Of High-Speed Railway Subgrade Coarse-Grained Filler During Freeze-Thaw Cycles

The high-speed railway subgrades in the seasonal frozen soil region of China have experienced different degrees of frost heave,and the frost heave of some sections exceeds the standard.The water-heat-vapor effect of high-speed railway subgrade coarse-grained filler is studied,and the frost heave mechanism of coarse-grained soil is more comprehensively understood.It is of great significance for the anti-frost design and construction of high-speed railway subgrade and the remediation of high-speed railway subgrade freezing damage in existing frozen soil region.Therefore,this paper selects the fine breccia gravel rock of the bottom of the subgrade bed of Haqi?s passenger special line as the research object,and through indoor experiments,and studies the effects of freez-thaw cycle times,compaction degree,cooling mode and other factors on soil temperature and water distribution,and analyzes the role of gaseous water in water vapor migration and the effect of water vapor on the high-speed railway subgrade in frozen soil region.The main contents and achievements of the thesis are as follows:(1)Aiming at the needs of experimental research objectives and content,the water vapor migration tracking device of soil under freeze-thaw conditions was independently developed,and the reliability of the device was verified.The freezing experiment of coarse-grained soil in closed system was completed by using this device.The effectiveness of the image tracking frozen front method is analyzed,and the error is within 9 mm.(2)The experiment of water-heat-vapor effect of coarse-grained soil under different cooling mode was carried out.The effects of water vapor migration and cooling mode on the water-heat-vapor effect were analyzed.The experiment results showed that the cooling mode has little effect on the moisture content of the frozen front,and the difference is 0.16 %.It has an important influence on the vertical distribution of moisture content in the frozen depth range.The grading cooling mode has a larger water replenishment than the constant temperature cooling mode,and the maximum is 2.66.Under different cooling modes,the migration height of external liquid water is in the range of 10~20 mm.Therefore,gaseous water migration plays a major role in water distribution.In the frozen soil engineering,uneven temperature variation of the southern and northern slopes of the subgrade in the frozen soil region may promote the distribution of uneven water in the soil.It is recommended to consider the influence of the migration of gaseous water and preventive measures.(3)The water-heat-vapor effect experiments of coarse-grained soil under different freeze-thaw times and different compaction degrees of freeze-thaw were completed,and the effect of moisture content distribution of different freeze-thaw times and compaction degree in frozen soil area and unfrozen soil area were analyzed.The experiment results show that when the degree of compaction is the same,the more freeze-thaw times,the greater the frost depth.After 6 freezes,the frost depth value increased by 18 mm compared with the initial freezing;the moisture content of the cold end of the soil sample decreased with the decrease of compaction degree and the increase of the number of freeze-thaw cycles.The moisture content at the frozen front increased with the decrease of compaction degree and the increase of the number of freeze-thaw cycles.It is recommended to control the compaction quality in the project to prevent uneven frost heave deformation of the subgrade in a frozen environment.