Evaluation of permeability, karst development potential and karst conceptual model of Ghareikan dam construction – Razavi Khorasan

Due to the complex hydrogeology of karst areas, the sealing of dams in such areas is more difficult, time-consuming and expensive, and the possibility of water leaksge is higher. After the dewatering of the Gharetikan dam and appearance of downstream springs and the leakage of water from the abutment of the Tirgan limestone formation, the possibility of karst development is considered to be the most important problem of this dam. In this article, the potential of karst development in the area and supports of the Gharetikan Dam has been studied by carrying out geological studies, structural geology and joint studies, geotechnical permeability and analysis hierarchy method (AHP).. The results show that about 14.6% of the ​​Gharetikan dam area has a high potential for karst development. The area of ​​Gharetikan dam area is affected by the Sarroud fault zone system, which has caused the collapse of the left side of the dam axis. The joint studies in the abutment of Gharetikan dam show three main types of joints. Two groups of joints are located at the intersection with the dam axis and the slope of the other group of joints is towards the dam basin. The investigating of Lugeon permeability tests in the dam construction shows that the highest permeability can be seen in the left abutment with turbulent flow, and then under the river bed with linear and turbulent flow, but there is no permeability in the right abutment. And the flow is mostly linear. According to the structural-conceptual model prepared from the location of the Gharetikan dam, to the location of the dam axis in the Sarroud fault system, and the amount opening and the slope direction of the joints in each station, it is expected that the amount of water leakage and escape and the possibility of karst development from the left side and the bed of the dam will be more than the right side of the dam.