Three-Dimensional Seepage Characteristics of Reservoir Embankment Considering Interval of Horizontal Filter

Recently, the deterioration of reservoir embankments has progressed severely; thus, a more efficient design and construction method for deteriorated reservoir structures is required. For a fill-type reservoir embankment, a method that employs intervals between the horizontal filter and the embankment has been used and shown to achieve an efficient design. Since the horizontal filter is an important structure that provides stable drainage during an earthquake or concentrated leak, it is necessary to examine any change in the seepage characteristics depending on the filter intervals. In this study, the seepage characteristics of a reservoir embankment were examined according to the filter interval range via 3-D finite element analysis; additionally, potential risks such as those from piping were reviewed relative to the design interval of structurally stable filters. Consequently, results showed that the maximum filter intervals to yield efficient seepage characteristics were within 0-20.5 m for the pore water pressure of the core and the height of the seepage line. The piping evaluation results, as based on the range of the critical hydraulic gradient (I-cr : 0.8-1.4), demonstrated that the piping maintained stability within the filter interval range of 0-20.5 m; applying this range, stability was maintained when filters were installed throughout the embankment. However, when the filter interval exceeded 20.5 m, the piping was observed to fluctuate between stable and unstable conditions according to the range of the critical hydraulic gradient. Thus, to ensure structural stability, this study has proposed a decision method for the interval of horizontal filters based on the results of 3-D seepage analysis and the theoretical range of critical hydraulic gradient.