| Red clay is one of the most widely distributed special soil types in our nation. Its poor physical and hydrological properties bring enormous geological disaster to our country roads, railways, bridges and engineering lines. The engineering practice found that the engineering properties degradation of red clay, its development zone's cutting slope instability, collapse, roadbed uneven settlement of such engineering geological problems in a largely caused by the water's long-term or cyclical or sudden action results. The properties and existing form of water, its action mode and effect degree with red clay are the key factors in the influence of effect degree, development characteristic and engineering properties of the red clay.This article is targeted at the typical south red clay of the Three Gorges Reservoir area, summarized the geological development background, growth conditions and distribution regularity of the red clay around Hanglan Expressway Portland area, investigated the types and characteristics of geological disasters induced by the red clay, concluded and analyzed main engineering geological problems and its characteristics in the development area of red clay. On the basis of this, carry out the research of red clay soil water features.Traditional research on red clay is mostly focused on macro field, paid attention to its physical properties and engineering degree of harmfulness. As more and more difficulties to explain the engineering problems in application of classical soil mechanics, Geotechnical engineers has paid more and more attention to saturated problems so that carrying out the unsaturated characteristics problem study of the special soil which has practical significant meaning and frontier.This paper is not only used macro analysis method, application of physical and mechanical experiments to discuss the physical properties rules of the red clay in work places, but also developed the soil water characteristic curve experiment to discuss soil water interaction characteristic and its influencing factors in three-phase medium. It is also applied X-ray diffraction, chemical full analysis, environmental scanning electron microscope, hot heavy/differential thermal analysis and so on to explain and analysis the interaction mechanism of soil water. Finally take the microscopic quantitative words analysis with application threshold segmentation method, take prediction of the soil water features curve with the application of VG model and also take prediction of the saturated soil infiltration in the application of mathematical methods which is based on the various state of the infiltration test of saturated soil.Main achievements are:(1) Red clay physical and mechanical properties are influenced by diagenetic environment, geographic location, formation conditions and other factors. Along the depth direction, the red clay's moisture content, void ratio, compressibility factor and free expansion performance in generally increases with increasing depth and oppositely the cohesion, internal friction angle intensity index decreases with increasing depth and the consistency of state changes from a hard Plastic into a plastic, soft plastic. In the horizontal direction, water content and compressibility index of red clay are lower in higher place than the lower place, but the strength parameters are higher in the high topography relative low-lying land. Along the depth direction, the physical index has a clear demarcation point in where the physical and mechanical properties reach to the worst and is the slope slippery zone.(2)The soil and water effect of red clay is influenced by the micro-crystal phase and structure feature. Its fine granularity dispersion, false grain of sex and false powder characteristics make its microstructure under electron microscopy showed reunion effect that is the main reason that increase the physical properties such as the red clay's porosity ratio and liquid plastic limit, the high mechanics effect such as cementation, structural connection strength and low mechanics effect such as compressibility, and the strong performance of surface activity and water sensitivity.(3)The main sticky mineral in red clay is montmorillonite, illite and kaolinite. Its main chemical composition is silicon, aluminum and iron oxide. The red soil effect is statistically significant. In micro-structure, shows the single grain, the joint development characteristic; face-face side-face, point-face contact relationship are both development; the connection strength between grains is weaker and the water-sensitive is stronger than the single-particle, often with the effect of rainfall infiltration, that is the main reason for the stability of the soil.(4)Red clay soil water characteristic curve is influenced by the initial state of the soil.With different initial moisture content, the same suction water status under the corresponding generally shows "â–³" font development when design the f Initial moisture content to the optimum moisture content, the soil water storage coefficient is the lowest, the dehydration rate is the slowest and the water storage performance is the best. To design the optimal moisture content as the basic point, with initial moisture content increasing or decreasing, under the same matrix suction corresponding saturation are both tending to be regularly decreasing.With the increase of dry density, different moisture states that the law does not express the same reaction. Analysis proves that when discussing the relationships between dimensional state and the Matrix suction, for the questions that density condition is different lead to the difference of soil pore space and water quantity, it's not reasonable to use the water quantity of moisture content to represent and measure the gravity of the earth and water characteristic curve change law, but it's more appropriate to use the relation between saturation and suction curve to explore the problem. Therefore, in the same suction conditions, with the dry density increases, although the soil water content decreases, the water loss rate decreases, saturation increases, dehydrate is difficult, dehydration rate reduces, water absorption ability enhances and water holding gets good performance.With the reduction of fine particle content, soil particle size increases, the soil intake value reduces and water coefficient increases. Within less than 0.05mm in diameter, soil agglomeration effects to some extent affect the soil-phase media interaction.(5)Using the micro test methods, qualitative and quantitative analysis both prove that the interaction between the soil pore structure and soil water in the red clay soil has contributed, explained and analyzed soil water interaction.(6)Using the field single-loop method and laboratory variable head permeability test to measure the different states of soil permeability and analyze the different states of the coefficient of permeability of unsaturated soils in applying of the calculated soil water characteristic curve. The results show that from the saturated to unsaturated soil, the permeability coefficient of red clay is decreased in varying degrees. The unsaturated hydraulic conductivity is not a single value, while is effected by the soil particle's pore structure, saturation, matric suction. The basic function law and influencing factors of soil water features is anastomotic.(7)Adopting VG mathematical model to predict the unsaturated soil water characteristic curve fitting is accuracy and feasible... |
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