Document Type : Research Article
University of Tabriz-Water engineering department
University of Tabriz,,- Department of Water Engineering
Department of water engineering, Tabriz University, Tabriz, Iran.
In design of hydraulic structures cutoff walls are needed for reduction of uplift force and exit hydraulic gradient. Upstream cutoff wall is used for reduction of the uplift force and downstream cutoff wall is used for reduction of the exit hydraulic gradient. This study tends to numerically investigate the double-cutoff beneath the hydraulic structures with variation in their location, distance and depth. Governing equations with boundary conditions are solved using the finite element method (FEM). Results showed that if the downstream cutoff wall is deeper than upstream cutoff wall, the resultant of uplift force would be more than the uplift force without cutoff walls. With a constant value for hydraulic structures width (B), decreasing in distance between two cutoffs (L), results the reduction in uplift force. Increasing in impermeable depth (D) and reduction in B, yields lower uplift force. Increasing in downstream cutoff depth (d2) and L, results reduction in exit hydraulic gradient (GR). When the two cutoffs are located in the end of the hydraulic structure, GR is lower than that when the downstream cutoff is located in L/B=0.33 and L/B=0.66 from upstream cutoff. Comparison between the available analytical solutions for two equal ending cutoffs with FEM, showed that FEM can predict PC and GR with maximum 5% error.