Experimental Study On Water And Salt Migration In Sulfate Saline Soil Isolation Fault Subgrade

As a kind of special soil,Qinghai saline soil has its own salt swelling,sinking and corrosion which will bring various hazards to the road construction.The location is a high plateau with a dry climate and little rain,where there are large temperature differences between day and night,long sunshine hours and high evaporation,and often accompanied by some characteristics of permafrost,which can easily cause various damages such as frost swelling and slurry during the spring thawing season.Therefore,the research on the water-salt migration mechanism of saline soil and the separation of fault subgrade by saline soil has great guiding significance for the treatment of saline soil diseases.In order to investigate the water and salt migration in saline soil subgrade with barrier layers in Qinghai province,this study conducted laboratory experiments to examine the water and salt migration at room temperature,tested a new type of two-layer geotextile and one-layer geomembrane barrier material,and studied the water and salt migration of various barrier layers under freeze-thaw cycles.,and the main findings are as follows.（1）In this paper,the water content of soil,plastic limit,liquid limit,plasticity index,maximum dry density and optimum water content of soil are measured through indoor tests;and the formulation of sulfuric acid saline soil is also carried out.（2）The water-salt migration test at room temperature proves that:under the confined environment not influenced by temperature,when the water content of the soil is the same with different salt content,the water in the soil hardly migrates,but the salt still migrates,and the salt gathers and migrates from the soil in the high concentration area to the soil in the low concentration area;when the water content and salt content of the soil are different,The water in the soil will migrate from the soil with high water content to the soil with low water content,and the salt will also migrate from the area with high concentration to the area with low concentration.（3）The experiment under the influence of wind proves that when the soil is not affected by temperature,the salt in the lower part of the soil body will gradually migrate to the surface,and with the closer the lower part of the soil body,the more the salt will be reduced;with the simulated"artificial rainfall",the salt will re-infiltrate.（4）The parameters of longitudinal and transverse breaking strength,longitudinal and transverse tearing strength,CBR top breaking strength,longitudinal and transverse breaking elongation,vertical permeability coefficient and mass per unit area and thickness of the new two cloths and one membrane material used in this paper were measured,which proved that the performance indexes of the two cloths and one membrane used in this paper still far exceeded the national and industry standards under the condition of thinner and lighter,even after the most unfavorable treatment.（5）By designing a temperature orthogonal device for water-salt migration under freeze-thaw cycles,the following conclusions are drawn:the soil temperature transfer has a hysteresis;latent heat of the water phase occurs during the freeze-thaw cycles inside the soil;under the influence of temperature,all water-salt will migrate to the freezing zone,and the water-salt content is larger the closer to the freezing zone,with a linear change;under the influence of freezing and salt expansion,the Na₂SO₄·10H₂O generated in the soil crystals,which open a channel in the soil,will make the water and salt infiltrate;the salt and water barrier effect of the two cloths and one membrane barrier is better than that of the gravel barrier;the displacement of the soil is smaller when the barrier is set compared with that without the barrier,and the displacement of the two cloths and one membrane soil is the smallest.