| The western region of Jilin Province is located in the southwest of Songnen Plain in China.It is one of the most serious areas of salinization in China,and belongs to the typical seasonal frozen ground in the northeast China.Seasonal frozen soil is a four-phase geological body composed of soil particles、liquid water、ice and gaseous water.In the freezing of soil,the water and salt in the soil will migrate and cause different degrees of diseases such as agriculture and animal husbandry、environment、water resources、foundation engineering,etc.Salt expansion,frost heaving and frothing will lead to subgrade cracking、uplift and swelling,thereby reducing the stability and strength of the roadbed.The study of water and salt transport has attracted more and more attentions,this research not only contributes to the advancement of theoretical research on water migration in unsaturated soils,but also has a great impact on soil salinization,and provides the technical support and theoretical basis for the varying degrees of frost heaving damage and road disease control in winter,which is of great theoretical value in controlling soil salinization and preventing the degradation of agricultural ecosystem.In this paper,saline soil in Nong’an County of Jilin Province was used as the experimental study object.The physical composition and basic physical and chemical properties of soil samples in the study area were tested and analyzed,and the water migration test was carried out by indoor direct method and temperature gradient freezing method.Based on the interrelationship of water、heat and salt migration,the coupling mathematical model of water 、 heat and salt transport in saline soil under freezing conditions was established by referring to the theoretical results obtained in previous studies and combining the energy and mass conservation equation.The finite element method was used to solve the model,and the results were compared with the indoor test results,in order to verify the effectiveness of the model.The main research results are:1.Soil particle size components to powder and clay-based,mineral composition of a large number of primary minerals and a small amount of secondary minerals.The natural density of each depth of the soil is basically maintained at about 1.91g/cm3.The total amount of soluble salt decreased with the increase of depth,in which the total content of soluble salts in the surface layer was 1.69%.The composition of soil salt wasmainly Na2CO3 and NaHCO3,and the soil was weak carbonate soil.2.The direct capillary water rise test results show that the height of the capillary water rise is small at room temperature,and the higher the compactness of the soil is,the lower the capillary water rise height is.The result of moisture gradient test showed that the water and salt in the soil had migrated in the freezing state.The temperature gradient caused the migration of the bound water in the soil and was not the capillary water.The transportation of salinity to water as a carrier,and is influenced by temperature、solute potential and other factors,and the greater the compactness of soil is,the less the movement of water and salt is.3.Under the condition of freezing,the moisture、heat and solute transport at any point in the saline soil system are interrelated and interact with each other and form a complex water、heat and salt migration coupling system.The results of the proposed model are in good agreement with the experimental results,indicating that the model can simulate the actual situation better.4.Based on the engineering example,according to the principle of treatment,combined with the water and salt migration law and the underground hydrological conditions of saline soil,it puts forward the relevant treatment measures on the roadbed to prevent the occurrence of roadbed disease in salty soil areas. |
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