Soil Water Retentivity and Permeability of Unsaturated Sands
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概要
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Three experiments with different saturated conditions 'were carried out in order to examine the retentivities and permeabilities of unsaturated fine and coarse sands which are affected by pore air behaviors. First experiment (Exp. I) was done in the two iron boxes filled respectively with the unsaturated fine and coarse sands in a large rainfall simulator of the National Research Center for Disaster Prevention. An iron column packed with the unsaturated fine sand was used for second experiment (Exp. II). In these experiments, volumetric water contents were measured by a neutron moisture meter, and a tensiometer was used for measuring pressure heads. In third experiment (Exp. III), a small PVC column packed with the fine sand under a perfectly saturated condition was used. In this experiment, sampling and oven-drying methods for measuring volumetric water contents were employed, and pressure heads were obtained from the elevation with respect to a standard datum at which stands in a riser after draining for three weeks.<BR>Experimental results were shown as follows: 1) hysteresis effects are exhibited in soil water characteristic curve for fine and coarse sands, the relationship between hydraulic conductivity and pressure head for fine sand, and the hydraulic conductivity versus volumetric water content relation for fine sand; 2) an upper boundary of capillary fringe corresponds to the pressure head value at the disappeared point of the hysteresis effect in soil water characteristic curve; 3) there occurs a pseudo-saturated part due to entrapped air behaviors in soil water characteristic curve during desorption and then an air entry value depends on its development; and 4) the hydraulic conductivity of coarse sand increases extremely in low water content but that of fine sand increases gradually as the water content increases.
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