A Study On The Moisture Content Migration And Charactreristics Of Frost Heaving Of Saline Soil In The Western Of Jilin Province

The west area of Jilin province is the typical seasonal frost region in northeast area. The area is one of the worst areas with land salinization, and saline soil is mainly distributed in Zhenlai, Qian'an, Da'an, Changling, Tong yu, Qianguo and other regions. The soil salt primarily composed with NaHCO₃ and Na₂CO₃, and local area contains a little chloride and sulfate. According to the soluble salt content and salt composition, the saline soil in this area belongs to carbonic acid (alkaline) saline soil.The area researched is the seasonal frost region ,with poor soil physical and chemical properties , high pH value, high salt content, soil sticky heavy, poor permeability, vegetation serious degeneration are the characteristics of this area. In the high salinity regions, in the process of soil freezing in winter, the water transfers to the freeze front simultaneously with salt. When it is melting in the spring, in the influence of the surface strong evaporation, salt deposited explosively in soil, water and salt migration caused by the freeze-thaw sharpened the region soil salinization degree. Salinity-alkalinity and drought have always been the main factors of the agriculture development in this region. Therefore, in order to effectively control the soil salinization rising trend, researching on the action of freeze-thaw the soil water and salt migration has important theoretical and practical significance. Usually, highway subgrade uneven settlement, expansion, road pumping frost heaving and other bad roads disease of the saline soil area, also concerns with the saline soil salt frost heaving and other special properties. The consolidation project of the west land of Jilin province launched in 2008, by irrigateing the salinity-alkalinity wastland and transforming the middle-and-low-yielding fields, but a lot of diversion channels appear different degree of frost heaving disruption questions in winter, which caused many problems of channel management and operation. So the research on moisture migration and frost heaving of saline soil in west Jilin should immediately start, it is the theoretical basis of the regional governance salinity-alkalinity wasteland and ecological environment protection, which playing a positive role in speeding up the salt-alkalization treatment process.At present scholars have researched the chlorine saline soil and sulfuric acid soil of coastal,Xinjiang, Qinghai and Gansu etc .They have achieved many valuable research results. For Jilin western regions mainly contain carbonate in saline soil, scholars also have done some field tests and indoor researches, but the research mainly on agriculture and ecological environment field. Suffered the freezing effect, carbonic acid saline soil of this area water-salt transporting and frost heaving has its special laws. At present, the results of the research from the aspect of the changes of the soil basic properties and soil temperature etc. Analysis the rules of soil moisture transfer and frost heaving rules through internal and external factors are relatively fewer. In this paper, we had taken the carbonate saline soil samples in spring, summer, autumn of Da'an city and Zhenlai town in the western of Jilin province, combining indoor basic test and moisture transfer of large-scale simulation experiment to research the characteristics of the water and salt migration. Meanwhile by indoor test, the frost heaving properties of different salinity, moisture content and compaction degree and the soil samples of different temperature of carbonate saline soil were investigated. On the basis of using gray relation analysis method and rough set theory, ensure the influence factors of carbonate saline soil frost heaving characteristics, set up the BP neural network of carbonate saline soil frost heaving forecast model, and add to verify this model.This paper mainly focused on the following job:1.Soil composition, physical and chemical properties and pore distribution characteristics of saline soil, moisture transfer of carbonate and frost heaving characteristics have important influence. Through researching the areas of different seasons, different depth of the soil routine test and research in this artical, we analysis the physical and mechanical properties of soil mass distribution features and the change rules of according to the season of the soil on a flat and longitudinal profile, at the same time the test research of its pore distribution characteristics. Test results show that: The soil particle size is mainly distributed between 0.005⁰.075 mm powder particle range of the research area. Some soils with disperser or not have no serious differences of powder and the viscous grain content. And some soil samples have many differences, with the "false powder sexual" phenomenon. Study found that the reason for this kind of phenomenon is that the salt content of different depths soil is different, and the exchangeabal sodium content is relatively bigger. Soluble salt content of the most soil samples about 30cm away from the surface is total more than 0.3%, and itself contains much exchangeable sodium, so the'false powder'phenomenon is not obvious. Poor soil reunion properties, when they dissolve in water, particle itself has strong dispersion, there is much thicker integrating-water film around the particles, which obstructs the rise of the capillary water. Meanwhile, the deep soil has poor permeability and good holding water permeability because of the higher viscous grain content of soil. The depth away from the surface 50¹00cm soil salt content is low, exchangeable sodium content is less,'false powder'phenomenon is obvious. The soluble soil samples themselves have weaker soil particle dispersion, thinner bound water film around the particles formed, thus the pores of the soil provides channels for the rose of the capillary water.The soil porosity of the research area is lower, which is between 26.6442%³9.1387% range. Most soils samples of research areas mainly have the capillary pores of aperture<0.1 mm, the micro pore of fuzz pipe diameter<0.002 mm can reach the highest content 56.7602%. Bound water film surrounding the soil particles will be full of pore and prevent capillary water migration, so the capillarity phenomenon is very weak. Through researching the soil samples of the research area in different seasons, different depth, the results show that: in the spring, because of the drought windy climate, the evaporation is hard so the water goes with the salt left and the soil salt content has large accumulation on the surface; In summer, duo to the rain eluviation, surface salt migration with moisture goes down. But the soil depth away from the surface 30cm has poor permeability, so the soil in depth of 30cm is in the higher salt content level; In Autumn, because of the influence of evaporation, the salt adds to the surface; In Winter, the deep freeze function makes the lower water migrating to the freeze cover, constantly with salt migration. When the spring coming again, strong evaporation makes salt accumulate to the surface again . 2. Adopting the temperature controlled fine water locator ,we have the indoor water transferring of large simulation test of direct method and freeze-thaw method in the research areas, through the contrast analysising of the soil which has been freeze-thaw for once or many times, researching the characteristics of the water transferring of single and multiple process of freeze-thaw cycles. Research indicates that because of the high viscous grain content of the study area ,so the clay soil porosity mainly Hansen pore , the soil tube containing a lot of exchangeable sodium, and the cationic exchange function makes the thicker integrating-water film around the particles, the overlap water film continuing to expand, blocking the capillary water rising channel, so the direct method test capillarity is seriously weak. In the freeze-thaw tests, multiple freeze-thaw cycles and a single freeze-thaw cycle of the capillary water rising test shows that the changing rules of moisture content changes with height is not obvious and the water content curves has not significant differences. The water transferring near the temperature are mainly the film water transferring caused by temperature gradient. But the salt transferring phenomena are the results of the temperature gradient and concentration gradient. The compaction degree is bigger, the salt migration rule relatively obvious.3. After researching the microstructure changes of soil freezing process in the study areas, we know that: once soil frozen, the soil particles becomes the flocculation shape or reunion shape structure, the pores between grains are larger and there are salt crystallization in them. And the style of the connection is mainly cementation links link form. Through the analysis of the same compaction degree, different freezing temperature microstructure pictures, we found that the lower freezing temperature, the looser of the structure of the body of the cell. If pore volume arranged inflation, the soil becomes looser and the change rules of different compaction degree soil sample appears somewhat different morphological rules. After researching the pore diametersize changes of the soil samples frozen or not, we found on the condition of the compaction degree 90%, the soil distortion ability is stronger. This is mainly because the development of the salt crystals and ice crystals influence the different compaction degree soil samples under the process of the soil freezing.4. According to the results of the physical and chemical properties, moisture transfer simulated test and the changes of the characteristics of microstructure, we comprehensively analysised the frost heaving influence factors in west Jilin province. We also proceeded the indoor frost heaving experiment of the closed system with carbonate saline soil and studied the influence of the different properties to the two areas on the temperature, moisture content, compaction degree and salt content factors. During the test process, we found that the salt expansion phenomenon of carbonate saline soil is relatively weak, which is caused by the temperature dropping. Under the certain salinity and certain moisture content, frost heaving rate of soil sample increases with the higher compaction degree, and the compaction degree has large influence of the soil samples with smaller moisture content while smaller influence of the soil samples with larger moisture content. The changes of temperature seriously affected the soil freezing expansion rate, with the temperature gradually reducing, the frost heaving deformation of soil with the salinity increases gradually. When the temperature dropped to -10℃, the deformation is basic stable, but the temperature range of frost heaving deformation of each salinity soils is drastically different. Different soil salt content, so the eventually frozen rate obviously different, the larger salinity, the lower freezing point , the duration time of freezing function also longer, so the final frost heaving rate is also bigger. The frost heaving rules of soil samples in Sanzhigou (spring) and Da'an (spring) are similar, but on the whole, the frost heaving rules of soil samples in Sanzhigou (spring) region is slightly lower than that of soil samples in Da'an (spring). One reason is that the test is indoor closed system frost heaving test, and the viscous grain content of soil sample in Da'an (spring) is high, spicific surface is high, hold water ability of soil is strong , so its final frozen bilge rate than Sanzhigou (spring) soil samples. It also shows that the soil powder viscous grain content and specific surface area influence soil frost heaving characteristics. Overall, the lower freezing temperature, higher salt concentration, higher moisture content and larger compaction degree made final soil frozen bilge rate increase.5. By using the gray relational analysis method and the rough set theory to analysis the correlation of the powder content, viscous grain content, cation exchange capacity, specific surface area, salinity, moisture content, compaction degree and freezing temperature of these eight factors with the freezing expansion rate, obtained that freezing temperature, moisture content and compaction degree, salinity and viscous grain content largely influence freezing expansion rate. Because most of the studied soil samples were from the same longitudinal profile, their physical properties were relatively close, and three other factors (specific surface area, powder content, cation exchange capacity) and viscous grain content have overlap function to frost heaving properties, so the specific surface area, cation exchange capacity and powder grain content were reducted in the evaluation and analysis of the affecting factors.6. We chose five main parameters that influence soil sample frost heaving rate through the gray connectedness method and rough set theory: Salinity, moisture content and compaction degree, viscous grain content and temperature as the input layer, frozen bilge rate as the output layer to establish three layers of BP neural network frost heaving forecast model. We chose 90 samples of BP neural network model among the 1218 test samples to train. And then select 20 samples with larger frost heaving rate to verify. The results show that the freezing expansion rate produced by the frost heaving trials is very close to the frozen bilge rate predicted with actual model, and the error between them is smaller, high precision of convergence results, this reveals that using gray relational method and rough sets theory to certain the relationship between the temperature, moisture content, compaction degree, salinity, viscous grain content these five parameters and the freezing expansion rate is precise, so the model based on this can well descript and predict carbonated saline soil frost heaving characteristics.