Nowadays, concrete or great earth dams are considered as the most important hydraulic structures that play a main role in providing required water for human societies. Therefore, the important parameters in stability of dams have been greatly considered recently by engineers of designing concrete dams. The issue of increasing the rate of permeability and exceeding over the maximum rate of allowed permeability is considered as one of the factors of instability of concrete dams and destruction of them. One of the risks of concrete dams is boiling phenomenon in the low stream of the dam. This phenomenon is greatly dependent on the lines of passage current beneath the dam and the network by which transmitting rate is possible to be obtained. In order to control the current of cut off sheet, changing the flow is usually used. This layer in different points under the dam has a great impact on water flow under the dam. This study aims at analyzing the effects of geometric features of the cut off layer on the transmitting flow net beneath the concrete dam and finally the permeation rate of and permeability in the vertical and horizontal line. And after modeling by using PLAXIS2D and parametric analysis of the model different situations will be compared with each other.
