| Summary: | 碩士 === 國立臺灣海洋大學 === 河海工程學系 === 103 === Groundwater resources has been one of the most important water resources in Taiwan. Globally, the amount of water in the unsaturated zone located between the water table and the ground surface represents only a small portion of the total water. However, because the unsaturated zone forms the necessary transition between the atmosphere and large groundwater aquifers at depth, the movement of water within the unsaturated zone of hydrological cycle is significant and plays a critical role in the geotechnical engineering. In this study, the numerical solution of groundwater flow in unsaturated layered soil using the Richards equation is presented. All the studies showed that the unsaturated flow is a highly non-linear process due to the high nonlinearity of soil water characteristics and soil permeability and various boundary and initial conditions. To solve one-dimensional flow in the unsaturated zone of layered soil profiles, the flux conservation and continuity of pressure potential at the interface between two consecutive layers are considered in the numerical model. A linearization process based on the Gardner's exponential model for the nonlinear Richards equation to deal with groundwater flow in unsaturated layered soil is derived. In addition, a novel method, named the Dynamical Jacobian-Inverse Free Method (DJIFM), with the incorporation of a two-side equilibrium algorithm for solving ill-conditioned systems with extreme contrasts in the hydraulic conductivity is proposed. The validity of the model is established for a number of test problems by comparing numerical results with the analytical solutions. The results show that the proposed method can improve the convergence and can increase the numerical stability for solving groundwater flow in unsaturated layered soil with extreme contrasts in the hydraulic conductivity. It is expected that the proposed model can be used to apply for more sophisticated groundwater flow problems in unsaturated layered soil in the near future.
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