FINITE-ELEMENT ANALYSIS OF UNCONFINED FLOW-THROUGH NONHOMOGENEOUS MULTI-ZONED POROUS-MEDIA

The flow of liquids through porous media is an important aspect of geotechnical engineering, There are several methods of solving the steady-state seepage problem. Methods which use potential theory with subsequent description of orthogonal sets of equipotential and flow lines, are suitable for confined flow through homogeneous bodies. Several mapping techniques are also used to extend the use of potential theory to how through nonhomogeneous media, but these techniques have limited applications. The finite element method (FEM) provides a powerful tool for seepage analysis through ground media. It enables direct evaluation of fluid pressures and flow rates and avoids laborious sketching of flow nets. The FEM is particularly convenient in analysing seepage problems with complex geometric boundaries, free surface and non-homogeneous ground conditions. The ANSYS finite element package is not capable of directly solving seepage problems. However, as the governing differential equations of seepage and heat transfer are directly related, the paper describes in detail how to simulate seepage using steady-state heat transfer method of analysis. A complex MACRO file was developed and interfaced with ANSYS for the solution of confined and unconfined fluid flow through multi-layered or multi-zoned non-homogeneous media. Practical examples, as well as applications to real engineering projects, are presented to demonstrate the efficiency, applicability and accuracy of the method. Special attention is given to the speed at which a free surface can be determined, in addition to the accuracy in describing surfaces of seepage and free drainage. Sensitivity of the analysis is discussed in relation to 'infinitely far' boundaries.