One of the important issues in soil dam design construction is controlling seepage from the body and foundation of the dam for stability secure and prevention of piping and water loss. The seepage through the foundation of earth dams can be controlled using cut-off walls. this study investigates the efficiency of the cutoff wall on some design parameters in the Sabalan rockfill dam. For this purpose, different positions of cutoff walls with various depth and permeability were used in the non-isotropic foundation of the dam. The results showed that the maximum hydraulic gradient in the foundation of the Sabalan dam occurs at the cutoff wall. Change in cut-off wall position for obtaining minimum hydraulic gradient showed that the optimal position of the cut-off wall for reducing the hydraulic gradient is in the toe of the core and the optimal position of cut-off the wall for reducing the seepage is in the heel of the core. By reducing the permeability and increasing the depth of the cutoff wall, the hydraulic gradient is increased and the seepage is decreased. Comparison of the effect of permeability and depth of the cutoff wall on seepage with corresponding values in Karkheh embankment dam, showed proper agreement between them.
