Numerical analysis of unsaturated flow in porous media
Abstract
There is increasing evidence that fluid infiltration and drainage in geotechnical structures cannot be accurately predicted using models that neglect the saturation of the soil. Most of the currently available models of unsaturated flow in porous media are either one-dimensional models developed in the fields of soil physics or agronomy, or two-dimensional models to assess seepage in earth dams. These models are insufficient to predict the patterns of pore pressures and quantities of flow in more complex structures such as pavements or landfill liners and covers. A critical examination of available models has shown in particular that in view of modeling unsaturated flow in complex geotechnical structures, the following factors are critical: rate of drainage does not only depend on the hydraulic conductivity but also on the capillary fringe; due to the non-linearity of soil hydraulic parameters such as conductivity and water retention, the use of piezometric heads or pressure heads alone, to assess convergence of a numerical algorithm for the Richards governing equation, may be misleading; truncation errors associated with currently used convergence criteria are important with heterogeneous soil profiles. To overcome these difficulties a new finite difference formulation is proposed and numerically implemented for a computer environment. The developed numerical model associates in a single algorithm the local and decomposed finite difference formulation of the Richards equation of transient unsaturated flow in porous media. The numerical solution is achieved for the case of two-dimensional incompressible flow and programmed under the form of a user friendly software, PURDRAIN. Different hydraulic material models (e.g. the Brooks and Corey and the Van Genuchten models) are discussed and made available to users in the PURDRAIN program. Validation of the model is achieved by comparing its results to previously experimental results. Finally, the applicability of the developed model is demonstrated for typical examples cases and the influence of the principal material and computational parameters is discussed.
Degree
Ph.D.
Advisors
Bourdeau, Purdue University.
Subject Area
Civil engineering|Mechanical engineering
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