Abstract
Some facility for the prevention of piping, reducing exit gradient and seepage amount under hydraulic structures, is construction of cutoff wall and drain. Therefore, this study compares the efficiency of cutoff wall on some design parameters in an assumed diversion dam cross-section. For this purpose, different placements of cutoff wall with various angle of inclination were used in the dam foundation. Results of this study showed that minimum uplift pressure happens when cut off wall is in the heel (upstream) of the dam. With fixing of longitudinal cut off wall placement, inclination of cutoff wall respect to the vertical position, results in reducing of uplift pressure. Effect of inclination of cutoff wall in upstream of the dam; respect to vertical position, in reducing of uplift pressure is very high.
Highlights
For dams built on permeable soil foundation, the water percolates through the soil and exerts uplift pressures and may carry soil particles with it leading to undermine erosion
Results of this study showed that minimum uplift pressure happens when cut off wall is in the heel of the dam
0.8 (b1/b) seepage flow would be in position which has 29.5 m distance from upstream of the dam
Summary
For dams built on permeable soil foundation, the water percolates through the soil and exerts uplift pressures and may carry soil particles with it leading to undermine erosion. A dam founded on permeable soil has to be designed against uplift and piping. The water seeping below the hydraulic structure exerts an uplift pressure on the floor. If the thickness of floor is insufficient, its weight would be inadequate to resist the uplift pressure. This may lead to bursting of the floor, and failure of the hydraulic structure may occur. Piping occurs if the exit hydraulic gradient at the downstream point approaches the critical hydraulic gradient. The exit gradient is said to be critical when the upward disturbing force on the grain is just equal to the submerged weight of the grain at the exit
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