Experimental Research On Water And Salt Migration Of Unsaturated Chlorine Saline Soil Under Freezing-thawing Cycles

There are a large number of saline soils distributed in the northwestern zone of China.The salt expansion,collapsibility and corrosiveness of saline soils bring a l ot of problems to the actual projects.And the climatic conditions in the northwest region are special.The annual rainfall is small and the evaporation is strong,the year temperature difference and the temperature difference between day and night are large as well as the positive temperature and the negative temperature alt ernate repeatedly.These cause the water and salt in the soil to migrate towards surface or shallow of the earth continuously and further exacerbate the degree of soil salinization.In order to explore the water and salt migration characteristics of sal ine soil under freezing-thawing cycles,this paper conducts freeze-thaw cycles on different salty saline soils through laboratory tests and analys es the water-salt migration of saline soil after different freeze-thaw cycles.1.Manually prepare chlorine saline soil indoors and compact the six saline soils with different salt content.The compaction results show t hat there is always a quadratic function relation between the water content and dry density of saline soil when the salt content is different.And with the increase of salt content,the maximum dry density of saline soil increases first and then decreases with the salt content of 7% as a turning point,and the optimal water content of saline soil keeps decreasing.2.Using the filter paper method to measure the matric suction of saline soil and draw conclusions through comparative analysis.The matric suction decreases first and then increases with the increase of salt content.But the effect of salt content is not obvious when the temperature is high.The matrix suction tends to decrease with the increase of temperature.The influence of positive temperature on matric suction is small,and the influence of negative temperature is relative ly large.The matrix suction decreases with the increase of water content.3.Through a comparative study on the salt measurement by drying method and conductivity method,it is found that both methods are very reliable.The measurement result of drying method is accurate and the measurement range is large.The conductivity method is convenient,and there is a linear function relation between the actual salt content of the soil and the corresponding conductivity of soil extract with soil-water ratio of 1:5.But the conductivity method can only measure the salt content of saline soil whose salt content less than 4%(including 4%).4.Conduct an experiment on water-salt migration of saline soil with different salt content under freezing and thawing cycles.The test r esults show that the water content of saline soil at the same position increases with the increasing number of freeze-thaw cycles.In the vertical direction of the soil column,compared with the initial salt content,the salt content at different positions is increased or decreased.The law of increase and decrease with freezing and thawing cycles is different between lower three positions of soil sample whose salt content l ess than or equal to 3% and great than or equal to 5%.5.By researching and analyzing the total suction change characteristics of different saline soils with different salt content under freezing and thawing cycles,it is found that in the vertical direction of the column,the suction in the middle is large and the suction at both ends is small.The suction curve is similar to the concave curve opening to the left.At the same position,the suction of the soil sample decreases with the increase of freeze-thaw cycles,and there is a maximum of reduction after three freeze-thaw cycles.