Macroscopic And Mesoscopic Experimental Study On The Mechanism Of Water Migration Of Coarse Grained Soil Under Freezing-thawing Cycle And Load

China's high-speed railway construction is gradually developing to seasonal frozen areas.In order to prevent subgrade diseases,the deformation mechanism of frost heaving and thawing settlement of high-speed railway subgrade needs to be solved.The most important hazard factor affecting subgrade deformation is the migration and accumulation of moisture in subgrade under freeze-thaw cycles and loads,resulting in redistribution of subgrade moisture field,which in turn leads to freeze-thaw deformation.In recent years,the problem of frost heaving deformation of coarse-grained subgrade filler mainly focuses on the establishment of remote monitoring system,laboratory tests and numerical simulation of different influencing factors,and there are few related researches on comprehensive analysis of moisture migration mechanism of coarse-grained subgrade filler under freeze-thaw cycles and different load forms.By applying different external load forms to coarse-grained filler samples with different initial water contents that are open to water replenishment under freeze-thaw cycles,this paper studies the development and changes of temperature field,frozen depth development,water migration amount,water migration height,water redistribution and frost heaving and thawing settlement displacement under load conditions during the test.The test adopts fluorescent tracer technology to track the change of liquid water migration position,and combines with microscopic research methods.Through X-CT scanning sample before and after freeze-thaw coarse particle structure distribution characteristics,using Matlab to process X-CT images,CT values are extracted to characterize the density change and damage degree of the sample before and after freeze-thaw.The macro and micro experimental research methods are combined to explain the mechanism of moisture migration of coarse-grained fillers.The following conclusions are mainly drawn through indoor experimental research:(1)Samples with different initial water contents have the largest amount of water migration under static load,and the corresponding migration height of liquid water reaches the highest position under static load.(2)The soil displacement caused by dynamic load changes the most,reaching between 1 mm and 2 mm,and the sample under no load and static load hardly generates displacement.(3)The freezing depth of samples with initial moisture content of 3% is the maximum under different load forms.(4)Through the calculation and analysis of CT value,it can be concluded that the soil density and compactness of coarse-grained fillings increase generally after freezing-thawing cycles,the initial reason is that the compaction degree of soil sample itself is relatively low.