Seepage Through Rockfill Dams in Narrow Valleys Ali Soleimanbeigi 1 and Fardin Jafarzadeh 2 1 Graduate Researcher, Department of Civil Engineering, Shiraz University, School of Engineering, Shiraz, Iran; ali.soleiman@gmail.com 2 Assistant Professor, Department of Civil Engineering, Sharif University of Technology, Azadi St., Tehran, Iran; fardin@sharif.edu ABSTRACT: Seepage analysis serves as one of the most significant stages in the design process of an embankment dam. In two-dimensional (2D) seepage analysis of embankment dams, little or no attention is paid to the seepage through side abutments. Moreover the role of grout curtain extensions into the side abutments and abutment material properties are inevitably neglected when performing a 2D seepage analysis. In this paper, two and three-dimensional (3D) models of a rockfill dam during operation state are generated and several unsteady and steady state seepage analyses are performed using finite element method (FEM). The results obtained from 2D and 3D seepage analyses were compared with measurements from the instrumentation system installed in the dam body and foundation during construction. It is concluded that for embankment dams to be constructed in narrow valleys, 2D seepage analysis results are far from reality and considering 3D modeling of such dam sites is vital. Several design graphs were developed to calculate 3D discharge rates and hydraulic gradients from those obtained from 2D seepage analysis. KEY WORDS: 3D Seepage Analysis, Finite Element Method, Instrumentation, Rockfill Dam INTRODUCTION The study of 77 embankment dam failures occurred in the United States until early 1980s indicates that seepage piping accounts for approximately 50% of all dam failures, the majority of which progress within the dam embankment and foundation (Engemoen, 2003). When seepage rates or hydraulic gradients increases unexpectedly, undesirable conditions may prevail to progress the piping or internal erosion that leads to dam instability or ultimate failure. Despite several measures incorporated in the design process to control seepage and piping, inaccurate assessment of seepage rates, pressure heads and hydraulic gradients lead to improper design of seepage controlling elements. In this case study, two and three-dimensional model of a rock-fill dam were developed and several unsteady and steady state 522 Copyright ASCE 2008 From Research to Practice in Geotechnical Engineering Congress 2008 From Research to Practice in Geotechnical Engineering Downloaded from ascelibrary.org by University of Wisconsin - Madison on 04/30/13. Copyright ASCE. For personal use only; all rights reserved.