Effect of cut off wall on hydraulic gradient and seepage in the Sabalan rock fill dam by numerical simulation

Seepage and water flow is one of the most important factors in design of earth and rockfill dams. The seepage through the foundation of earth dams can be controlled using the cut off walls. The hydraulic head reduces in the connection zone of the cut off wall and core of the dam that results in high hydraulic gradients. Therefore, this study investigates the efficiency of cutoff wall on some design parameters in Sabalan rockfill dam. For this purpose, different hypothetical positions of cut off wall with various depth and permeability were used and analyzed in the foundation of dam. The results showed that the maximum hydraulic gradient in foundation of Sabalan dam, occurs at the cutoff wall. Change in cutoff wall position for obtaining minimum hydraulic gradient showed that the optimal position of cut off wall for reducing the hydraulic gradient is in the toe of the core and the optimal position of cut off 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.