A Steady State Model For Flow In Saturated-Unsaturated Soils
Papagiannakis, Thomas A.
A rigorous two-dimensional model is presented describing steady-state flow in saturated-unsaturated soils. 'The model considers continuous flow between the saturated and the unsaturated zone without differentiating between saturated and unsaturated soil. The governing differential equation is nonlinear, since the coefficient of permeability depends 'upon the pore-water pressure head. For the solution of the nonlinear differential equation an iterative scheme is used. Both the finite difference and the finite element methods are formulated and computer implemented. Various problems are considered involving different anisotropic and heterogeneous soil conditions. The results are found to be in good agreement with Casagrande's classic solutions based on the flow net technique. Calculation of the quantity of flow through various sections in different structures shows that there might be flow across the phreatic line. This demonstrates the superiority of the proposed flow model in comparison to traditional saturated-only flow models, which usually assume a flow line condition for the phreatic line. There is not as a result further need to retain the arbitrary categorization of flow problems in confined and unconfined or to rely solely on the flow net technique for their solution.