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.

Water hammer is a transient flow in pipes that was created by sudden changes of velocity in pipe lines. This phenomenon can cause strong positive and negative pressures in water conveyance pipes and usually it poses pipeline to danger. Overall, water hammer creates by rapidly closing valves, shutting off or suddenly restarting pumps. It has destructive hydrodynamic effects in pressurized pipelines. In this study, governing equations of water hammer is numerically simulated using MATLAB software. Then, the sensitivity analysis in negative and positive pressures by changing some variables such as pipe diameter, pipe length and also wave velocity in pipe was investigated. Numerical simulation is based on characteristic method. Sensitivity analysis help designers to have well understand of water hammer phenomenon.

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Seepage in embankment dams is one of the important factors in stability and dam's maintenance. Core in earth dam is essential for waterproofing and controlling of seepage. Therefore, selection of proper materials and sizes for core of earth dam are very important. Thick clay core is proper for waterproofing but because of low shear strength of the clay, it would be dangerous for dam's stability. The optimal core would be the core which has proper waterproofing, stability safety factor and also with economic condition. In this study, the aim is to determine the optimum size for clay core of Alavian dam near Maragheh city in steady state seepage condition. For this purposes, Geo-Studio pack is used for numerical simulation. In addition, simulation of seepage and slope stability for the built maps of the dam, 11 more models of the dam with different size of cores were tested to find the optimum core thickness. From these models, data required for objective function and constraints using regression techniques for seepage, hydraulic gradient and stability safety factor were provided. Results showed that optimized volume of the core is 35% smaller than the present core. Key words: Earth dam Optimization Clay core Excel solver Geo-Studio INTORDUCTION(FDM), the five-point approximation technique, has been Dams are one of the most important structure made The grid system, with computational boundary being by human that destruction of it may caused excessive coincident with the physical boundary, was numerically costs and sometimes irreparable. Destruction of the dams obtained by solving Laplace equation. The method was may be due to seepage from dam is one of the most applied to analyze the steady seepage in an earth dam. important ones. Seepage itself is not a destructive In this study, three different grid types were considered phenomenon and happens in all dams. But the point that and the results were compared with ones obtained by makes it dangerous is lack of proper controlling and analyzing with Geostudio [2] software. It showed that by forecasting of dam resistances. In non-homogeneous choosing small enough increments, the results are earth dams, waterproofing is a task for dam core. Use of satisfactory. Hasani et al.[3] used geo-studio software clay core for waterproofing the dam is most common.for seepage analysis in Ilam earth fill dam. In order to In the other hands, shear strength of the fine materials like evaluate the type and size of mesh on total flow rate clay is low and it would decrease the stability of the dam and total head through the dam cross section, four mesh against slope sliding. Therefore, use of thick cores is a size such as coarse, medium, fine and unstructured mesh good choice for minimizing seepage and prevention from were considered. demonstrated to deal with seepage problem in earth dams.