Dissertation > Agricultural Sciences > Agriculture as the foundation of science > Soil > Soil physics

Experimental Study on Soil Shrinking and Swelling Characteristics during the Alternative Drying and Wetting Processes

Author HuangChuanQin
Tutor ShaoMingAn
School Northwest University of Science and Technology
Course Soil
Keywords Alternating wet and dry Soil swelling characteristics Geometric factor Fractured area
CLC S152
Type Master's thesis
Year 2008
Downloads 152
Quotes 2
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The soil in the process of alternate wetting and drying will occur the phenomenon of expansion and contraction. The expansion and contraction of the soil affects the distribution of the pores, and thus may also make the moisture characteristic curve is changed. At the same time, the cracks in the soil shrinkage process of the formation to create the conditions for preferential flow, thus affecting soil water and solute transport. The size of the cracks in the process of expansion and contraction, the geometry of the assessment of the soil surface infiltration and soil moisture distribution is very important. Drying shrinkage of the swelling process in order to better study the expansive soil moisture, solute transport and soil swelling reduction of soil hydraulic characteristics and hydrological simple and reliable research methods, choose the appropriate expansion and contraction of the model is critical. In this paper, a special test device of the disturbed soil swelling characteristics of the different textures, its basis and thus more practical significance undisturbed soil study, comparing whether the fissures in the soil expansion and contraction process of expansion and contraction characteristic curve further swelling characteristics of soil. Main results are as follows: (1) disturbed soil expansion and contraction during the retention sections, the normal segment structure segment, the three linear model can better fitting than the curve of the volume and quality of the water content can be divided into its shrinkage and expansion characteristics of curve. Soil shrinkage, expansion curve in the characteristic values ??of each segment are less than 1, i.e. the soil volume rate of change is less than the rate of change of water content in the soil swelling and shrinkage process while. Found soil shrinkage curve of the undisturbed soil can be observed in addition stranded segment, the normal segment, structure segments, in water higher Shihai can be clearly observed to \(2) the different texture undisturbed soil at different heights processing measured drying shrinkage \\Undisturbed saturated water content of the soil, the specific volume of saturated by the sample density, i.e. sampling bulk density, the greater the saturated moisture content is lower, the smaller the specific volume of saturated soil saturated bulk density bigger. Substantially decreased saturated soil saturated water content and water absorption than the volume with the increase in height of the soil column. Contrast with disturbed soil, undisturbed soil structure makes the undisturbed soil drying shrinkage is less than the amount of disturbance of soil contraction, greater than the undisturbed soil relative water swelling disturbed soil. Field soil texture more viscous, the expansion and contraction of the soil the better, and the undisturbed soil disturbed soil expansion and contraction. (3) consider soil swelling shrinkage fissures the field soil shrinkage curve (black loam, for example) is more complex, but on the whole, the tested soil shrinkage curve can be divided into stranded segment contraction, normal contraction paragraph structure contraction segment pseudo-saturated segment. Expansion curve is still in line with the \Moist soil drying shrinkage first only the soil surface subsidence, fissures gradually increasing with the ongoing stress of the soil within the drying process, the process of soil shrinkage the fractured area increased with the reduction of water content, the soil drying shrinkage of the late, the soil the fissure increase slows the soil contraction obvious. When the dry soil is moist, the initial stage because of the presence of cracks, and the increase in the soil volume is three dimensional, after When fissures bridging of the soil, the soil volume increase is one-dimensional, only the soil surface upward. The expansion and contraction of the soil is anisotropic. (4) the contraction curve of the measured data according to the non-continuous direct soil determined using a piecewise continuous curve obtained by the Lagrangian interpolation method is reliable, to be able to describe the actual shrinkage process of the soil. Disturbed soil contraction and expansion curves can be carried out with the classic three-straight-line model fitting, undisturbed soil shrinkage characteristic curve can be divided into stranded segment normal paragraph structure paragraph and pseudo saturation segment, and the lighter soil texture, soil thickness Vietnam thin high water content of soil drying shrinkage curve \The contraction and expansion of the field soil is anisotropic. In addition, an easy to obtain a continuous soil shrinkage curve Sectional Lagrangian interpolation. In this study, to lay the foundation soil expansion and contraction process of quantitative research, and provide scientific support for soil preferential flow and pollutant migration studies.

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