Abstarct: Rock masses include various types of discontinuities, including faults, seams, stratification planes, and shear zones. Discontinuities are the most important stability controlling structures in surface structures. If the support does not have the ability to withstand the incoming loads caused by the dam, tank and other reaction forces in the environment, even if the structure is well designed, the project in question will not be implemented successfully and can cause risks to the surrounding environment. In arch dams, it becomes doubly important due to the nature of this type of dam and the double dependence on supports. Therefore, it is inevitable to study the resistance properties of the discontinuities and their position in relation to the supports before implementing the dam project. In this research, the stability of Pirtaghi arched concrete dam construction has been evaluated by examining its governing discontinuities. As it is evident, identifying the values of the forces acting on a rock mass is associated with many uncertainties, and in the meantime, the impact force is not an exception to this rule, in the impact forces acting on discontinuity plates, the efficiency of the sealing curtain has a direct effect on the amount of this force. . In the analysis carried out to better identify the stability of the support and reduce the effects of uncertainty, the sensitivity of the safety factor to the impact forces has been investigated, so that the wedges identified in the construction, under three different loading conditions due to the different efficiencies of the curtain Assessment has been made. Also, another result obtained from this analysis shows a direct relationship between the friction angle and the safety factor. In the construction of the mentioned dam, 5 wedges caused by the separation of faults and large joints have been identified in the right support and 1 wedge in the left support, the minimum safety factor obtained in the maximum loading conditions is equal to 1.2, which after comparing with the allowed safety factor In this loading mode (the minimum safety factor allowed in the maximum loading mode is equal to 1), the stability of the wedges is verified. The results of the analysis of the joints governing the construction also indicate the formation of wedges and the resulting wedges have a minimum safety factor of 1.9, which according to the difference between this value and the minimum allowed safety factor, they can be considered safe from the point of view of sliding on the edge.