Research On Dispersive Identification And Freeze-thaw Cycles Of Clay Soil In The West Part Of Jilin

In order to reliev the water shortage and the threatens to people's life and property by natural disasters, a large mumber of hydrotechnical constructions were builded all over the world, when they are serving human they also bring many engineering problems of dispersive soil. Dispersive soil is a kind of special soil, it scattered very extensive in the world, such as America, Mexico, Venezuela, South Africa, Brazil, Thailand, Israel. In China, Heilongjiang, Xinjiang, Jiangsu, Shandong, Henan, Liaoning, Jilin and Hubei and other provinces have encountered in engineering practices.Dispersive clay is dispersed in a low salinity of the water (or pure water), it has low capacity of resisting the seepage failure by pure water, so it provides the precondition to the seepage deformation and failure. Experts and scholars at home and abroad had made large amount of dispersivity test and studied on the dispersion mechaism aiming at these problems. They also proposed many effective prevention measures, such as lime treatment, control water cut and so on. Practice shows that these prevention measures can prevent dispersive soil erosion destruction. But because the infinite branch variety genetic of dispersive soil, the effects of prevention measures are different, even appeared some failure case. This shows that the study of dispersive soil is in adequate, it can not provide enough theoretical foundation to engineering practice. So studing on dispersive soil has very important theoretical significance and engineering significance.At present many problems still esist at dispersive soil research field. First, there has no accurate and simple identification method, commonly used methods have many human factors during experimental operation process, so we need to be empirical. Second, for high-sodic saline soil, there are many linitations when identifing soil with the existing identification method. FAN Heng-hui queried the identification standard of double hydrometer test, test for anion of solube salts of pore water and test for percentage of exchangeable sodium. Third, primary recognition has been abtained theoretically, but the research extent is much less than other common soil. The study on interaction mechanism of soil, water and salt is not deeply enough. So it is necessary to study on the engineering properties and dispersion mechanism and put forward more effective methods to provide conditions for the further development of engineering.In view of the above, it is necessary to study on the engineering properties and dispersion mechanism. This paper studies the soil in the key project of land exploitation and consolidation in the west part of Jilin province. We identified the dispersibility of soil by field investigation, the fundamental physical test, chemistry test, tests for identification of dispersive clay soils and freeze-thaw cycle test. On the basic of this, analyze the dispersion mechanism from clay content, clay mineral type, ph and percentage of exchangeable sodium. Study the relationship between the freeze-thaw cycle and dispersibility by freez-thaw cycle test.Firstly, soil physical, chemical quality trials were done. After analysis, it is considered that:(1) the particle component of 27 samples researched mainly is silt (0.005mm-0.075mm). (2)total soluble salt is 0.06%～0.55%, sodium ion is 0.012%～0.165%, potassium ion is very seldm, magnesium ion is 0.004～0.072%. The main anion is HCO3-. In summer, the most salt content appeared at 0.3m deepth, in spring and autumn it appeared at the surface. This is because in summer the soil leaching bring the salt to deepths of the field, and in spring and autumn, surface water are evaporated by the intensive evaporation.(3)PH of all sample is more than 7.Secondly, identify the dispersibilyty of soil sample with pinhole test, double-hydrometer test, crumb test and percentage of exchangeable sodium. Results shows that the saline soil in the west part of J(?)s dispersive soil, and the dispersibility from big to small is:Zhenlai(sum(?)> Da'an(spring)> Da'an(autumn)>Zhenlai(spring). From the comprehensive appraisal results we can see the dispersibility of soil is related to deepth and season. From up to down, dispersibility decreases gradually. From the comparison of summer, spring and autumn,we can see that dispersibility in autumn is the biggest.。 Once again, in order to find out if moisture migration and salt migration is related to dispersibility, we use the freeze-thaw cycle test. The result shows that freezing and thawing is related to dispersibility,after freezing, dispersibility increased, this is because the soil is salt soil,after freezing the porosity of soil become larger because of the salt expansion, attractive force between particals is minified, so the dispersibility of soil increased.At last.by the analysis on dispersion mechanism, we can get:first, clay particle content is not enough, cementing strength can not inhibited the dispersibility; second, there are a lot of sodium ions served as dispersant; third, strong alkaline increased the negative charge on the suface of soil particle, diffusion layer become very thick, the cementing strengh between particles decreased. Forth, freezing and thawing can affect the moisture migration and salt migration, so they can also affect the dispersibility of soil. Temperature gradient is the main dynamic of salt migration. With the salt migration, exchangeable sodium accumulated to the ground surface continuously, this variation can also increase the dispersibility of soil. During frozen-thaw process, pore water freeze gradually with temperature decreasing, ice crystal can increase the pore volume, distance between grains increased, so the structure of soil changed, dispersibility of soil increase.