Percolação em barragens de terra em regime permanente e transiente com o método dos elementos de contorno

Abstract

The main purpose of this work is the numerical analysis of the seepage process through an earth dam. The transient free surface flow during the fill-up and drawdown phases of a reservoir is of utmost importance in the analysis of embankment stability and to compute the internal drainage devices. A boundary element procedure for dealing with steady and unsteady seepage flow with a free surface in homogeneous earth dams is presented. Special attention is given to the implementation of isoparametric quadratic elements, which improve curved geometric modelling capabilities and can obey the tangent condition at the interface between the free and seepage faces. Physical and geometrical discontinuities are treated with the use of special non-nodal-collocation elements with nodes at their extremeties but collocation points inside the element. Another emphasis is the inclusion in the computer code of Telles' third degree polynomial transformation, in order to improve the accuracy of Gaussian quadrature schemes in the near-singularity range. An adequate treatment of discontinuities significantly reduces numerical oscillations along the free surface making smoothing procedures unnecessary, even if an explicit time marching scheme is employed. The results are analised and compared regarding their accuracy and numerical behavior.