Experimental Study On Water-vapor Migration Of Coarse-grained Filling In Railway Subgrade Under Freezing Conditions

With the extension of high-speed railway construction to cold regions,the problem of frost heaving of subgrade in seasonal frozen soil areas has become increasingly prominent.And the main factor causing frost heaving of roadbed is the migration of water in soil.In the coarse-grained soil composed of subgrade filler,the gap between soil particles is larger,therefore,Capillary effect has little effect on water migration,so it is reasonable to assume that in coarse-grained soil,the redistribution of water during freezing may be related to water vapor migration.There are few studies on the law of water-vapor migration of coarse-grained soil,as a result,no consensus has been reached so far.The lack of a visualized water vapor transport system and associated test methods is one of the main reasons for limiting such research.In order to verify the existence of gaseous water migration in coarse-grained soil under freezing,and to reveal the law and mechanism of water-vapor migration and solve the frost heaving problem of cold roadbed,this paper proposes a study on the law of water-vapor migration under freezing based on fluorescein tracking technology.The test method was carried out,and the traditional frost heave test device was upgraded and developed,and a soil moisture migration measuring device system based on fluorescein and image tracking technology was developed.This device system is used to intuitively track the process of water migration,and the mechanism of water vapor migration of coarse-grained soil under freezing is studied.The effects of different initial moisture content on water redistribution under constant freezing and gradual freezing are analyzed.This paper has obtained the following conclusions and results through experimental research.(a)The developed device system mainly includes a double-layer hollow stacked ring type plexiglass tube,a liquid water isolation device,an image acquisition device system and so on.Combined with fluorescein tracer technology and image processing technology,the device system can meet the requirements of current experimental research on water migration and other frost heave.(b)Under the constant temperature unidirectional freezing of coarse-grained fillers,the migration of gaseous water exists in the coarse-grained soil,and the migration of gaseous water is the main factor causing the redistribution of water.Both the exterior water and the interior water will evaporate and migrate to the frozen front in the form of gaseous water.In addition,the initial moisture content has a large influence on the water redistribution.(c)Under the action of gradual freezing,the migration of water in coarse-grained fillers is dominated by gaseous water migration,external water recharge also enters the soil mainly in the form of gaseous water.The migration of external gaseous water and liquid water has its own range of influence.(d)Compared with the constant temperature freezing method,the gradual freezing method will have a larger freezing depth,the water content distribution inside the soil will be more uniform,the thickness of the ice layer will be more uniform,and the external water replenishment will not increase.