Reduction of Seepage Risks by Investigation into Different Lengths and Positions for Cutoff Wall and Horizontal Drainage (case Study: Sattarkhan Dam)

Seepage from the earth dam’s body reduces the amount of water in the dam’s reservoir and threatens its stability. In this paper, the earth-type Sattarkhan Dam on the Aharchai River has been investigated. In this regard, the SEEP/W model from the GeoStudio 2018 software suite was used for modeling. This study examines the effects of various lengths and positions of cutoff wall and horizontal drainage on seepage, uplift pressure, and exit gradient. Increasing the length of the cutoff wall reduces seepage in both sections, with a more significant effect on Section 2; it also decreases the uplift pressure and the exit gradient. Changing the position of the cutoff wall has a significant effect on seepage fluctuations in Section 1 but has no effect on seepage in Section 2; in positions 2 to 7, the uplift pressure values are nearly identical, and the exit gradient is most significant at position 1 and least at position 2. Increasing the horizontal drainage’s length increases seepage, reduces uplift pressure, and increases the exit gradient. The closer proximity of the horizontal drainage position to the dam’s core increases seepage and decreases uplift pressure and exit gradient. Finally, it is concluded that the construction of a cutoff wall and horizontal drainage with appropriate lengths and positions reduces risk and improves the stability of earth dams.