Influence of Drainage Filter and Cutoff Wall on the Seepage Characteristics of Earth Dam Using FEM

Abstract

The aim of this study is to investigate the influence of drainage filter and cutoff wall on the seepage characteristics of earth dams using the finite element method (FEM). The performance of horizontal drain, vertical cutoff wall and toe drain on the seepage flow and pore water pressure for a numerical earth dam has been investigated. Various horizontal drain lengths and toe drains are assumed. Cutoff walls having varying depths are positioned at different locations of the earth dam. Two core shapes have also been considered for this analysis. The position of phreatic line, seepage rate and pore water pressure have been computed through a numerical analysis by using Seep/W. Numerical results depict that, in the case of an earth dam without core, horizontal filter and toe drain help to bring the phreatic line down in the dam body but the cutoff wall alone is unable to do that. In the case of an earth dam with a core, the core helps to bring the phreatic line down in the body of the dam. With the increase of horizontal drain length and inclusion of toe drain, the seepage discharge increases but the pore water pressure decreases. The values of seepage discharge and pore pressure are lower in the case of an earth dam with a core. From the numerical analysis, it is observed that the best position of the cutoff wall is in the middle of the foundation with an internal core, because placing of the cutoff wall in the middle of the foundation gives lower values of both seepage and pore water pressure.