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This study, based on Richard Equation, attempts to analyze the behavior of water flow in unsaturated soils. Also, based on Biot''s consolidation theory, the subsidence of unsaturated soils during the flow infiltration in the soils is analyzed. An inverse function method with the Newton Raphson method is used for finding out the eigen values, and then solving for the water pressure as well as water content of the unsaturated soils. Meanwhile, the numerical solution of the unsaturated soils subsidence is obtained. An approximate solution of the unsaturated soils subsidence is developed for a comparison to the numerical solution.
For homogeneous soils, given the constant saturated hydraulic conductivity, the smaller the pore size distribution of the unsaturated soils is, the minor effect of the hysteresis phenomenon on the moisture content and pressure head of the unsaturated soils is; on the contrary, the greater the pore size distribution, the greater the effect of the hysteresis phenomenon. With the constant pore size distribution parameter accompanied by a greater saturated hydraulic conductivity of soils, the moisture content and pressure head of the soils will reach a steady state sooner. In terms of the settlement of the soils, when soils are in the wetting condition, the settlement of the soils decreases with a increase in the time length. On the other hand, in the drainage condition, the settlement of the soils increases gradually as time goes. When the pore size distribution of soils gets larger, the effect of hysteresis phenomenon becomes more obvious and the settlement of the soils takes place more slowly. However, the smaller the pore size distribution of soils, the more rapidly the settlement of the soils.
Given the constant pore size distribution of two Layered-unsaturated soils, if the saturated hydraulic conductivity for the upper layer soils is larger than the lower layer one, the moisture content and water pressure of the upper layer soils will reach a steady state faster that the lower layer one, and vice versa. When the saturated hydraulic conductivity for two layered soils is constant, the layered pore size distribution parameter will lead to a more obvious hysteresis phenomenon. Appositely, if the pore size distribution of soils is smaller, there will be a litter of hysteresis phenomena. In terms of the settlement of the soils, the large pore size distribution of the soils results int he more obvious hysteresis phenomenon and the less settlement of the soils. On the other hand, the smaller the pore size distribution of hte soils, the less obvious the hysteresis phenomenon and the larger the settlement of the soils.
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