Optimal Position of Apron and Cut off in Reduction of Seepage Factors in Foundation of Diversion Dams

Seepage of diversion dams foundation and importance of its control, has always been of interest to researchers. In this study, seepage parameters and their control, were investigated experimentally, numerically and analytically. Results showed that using apron and cut off were effective on reduction of seepage discharge so that model with apron and two cut off for upstream head of 47 cm, seepage discharge about 60% decreased and occurrence of piping postponed. Investigations showed that outlet discharge had direct relation with upstream water head. Using a cut off on dam foundation showed the best performance on reduction of uplift force and reduced about 22%. Also application of apron and two cut off beside the control of piping, decreased exit gradient for upstream head of 75 cm up to 0.763. Results for model of apron and cut off on foundation in control of seepage discharge was so similar to model of apron and two cut off, so it is suitable alternative in terms of economic instead of apron and two cut off. Numerical model had good agreement with experimental model on simulation of exit gradient, uplift force and seepage discharge for whole models and error was less than 5%. Results showed, when cut off located at the center of apron, flow line was more symmetrical, potential line and potential changes under the apron were less. Also results compared with different analytical models and Khosla method showed more similarity with experimental and numerical results.