عنوان مقاله [English]
Water seepage through foundation and abutments of dams is one of the most important parameters in design and construction of dams. Seepage endangers stability of dam in addition to lose reserved water. For this purpose, studies are done about permeability of the dam site rock masses and the sealing methods. Moreover, seepage of Tangab dam is discussed as a case study in this article. Based on the geological studies, three types of rock masses, i.e., Ilam-Sarvak, Kazhdomi and crushed zone, are distinguished in the study area. Kazhdomi Formation consisting of shale and shaly limestone underlies by Ilam-Sarvak limy formations. The crushed zone is located between these two rock units. Water seepage was evaluated according to the water pressure tests (lugeon) on these formations’ outcrops in the left and right abutments. Permeability of the rock masses interpreted based on secondary permeability index (SPI) considering the result of lugeon tests and the drilled core properties. Out of these three rock types, the crashed zone has the highest permeability, and Kazhdomi formation has the lowest permeability. In SPI classification, shale and shaly limestone of Kazhdomi Formation set on high class and need no improvement. But other rock masses need sealing due to the high permeability. Kazhdomi Formation can be counted as impervious bed to the dam site, thus grout curtain should extend to this formation. Results of the studies indicate that except of some cases, there is a reasonable correlation between SPI and RQD values. According to these results, type and composition of grout is suggested for construction of the grout curtain. The results also show that maximum value of water seepage occurs in the right abutment and if the grouting is successful, the seepage will decrease significantly.