Experimental Research On Moisture And Salt Migration Of Sulfate Saline Soil

The saline soil was regarded as bad soil in civil engineering,being used as subgrade filler,if necessary.The subgrade was easily suffered from collapsibility,salt expansion,frost heaving and so on.Primary cause of these diseases is agglomeration and migration of water and salt in subgrade.In this paper,on the combination of water and salt migration source,the soil column indoor test is design to make out the characteristic of water and salt migration.Water and salt migration features of different sulfate salt content under different levels of water content is analyzed at normal temperature condition and freeze-thaw cycles,the research are as follows:(1)By 8 groups sulfate saline soil compaction test of different salt content,the result show that the saline soil compaction curve is similar to soil compaction curve,with the water content increases,the dry density increases at first,then declines.For sulfate soils with different salt content,maximum dry density decreases with the increase of salt content,and the optimum water content increases gradually.(2)Advantages and disadvantages analysis of salt-leaching and drying method,TDR(time domain reflectometer)test system and ECH2 O conductivity testing system for sulfate moisture content and salt test.ECH2 O conductivity testing system was recommended as a test method for sulfate content and moisture content.(3)The soil-water characteristic curve of sulfate saline soil is determined by filter paper method,the relationship between different salt content and matric suction is analyzed.As the result showed that the higher is sulfate salt content,the greater is matric suction.It find that the exponential relationship between the matric suction and soil volumetric water content well.(4)Soil column indoor moisture-salt migration test results at normal temperature condition was performed and dynamic monitoring of water and salt was carried out.It reveals that salinity gradient is the driving force of water and salt movement,for the same moisture content,however,for the same salt content soil column,the moisture content difference is the power source of water and salt migration,and the greater is water content,the more obvious is migration.(6)Compared with the experimental results under normal temperature condition,freeze –thaw cycles have more effect on water and salt migration,which shows that the migration is more obvious under temperature gradient.With the increase of freeze-thaw cycles times,and aggregation phenomenon of water and salt accumulation on top are more significantly.(7)Based on the characteristics of water and salt migration in soil,the causes of soil secondary salinization and subgrade diseases are analyzed.On this basis,the prevention and control measures of the existing secondary saline subgrade diseases are summarized.