Design and construction of civil structures such as dams require deep understanding of geological and geotechnical engineering conditions of rock masses in their site. Doosti Dam site consists of sedimentary rocks such as calcareous marl, siltstone, sandstone and sandy limestone of Mesozoic (Cretaceous) and early Tertiary of the Kopet-Dagh basin. In this study, permeability and hydraulic conductivity conditions of dam site were evaluated based on Lugeon tests and were presented as maps. Additionally, rock mass discontinuities in dam site and their properties were determined. The effects of geological engineering properties of discontinuities and permeability of different rock units on grout takes in the grout curtain were assessed. To compare the results, grouting performance was presented in the form of iso-cement take curves in the curtain rows. Finally, areas with poor performance were determined based on the obtained information. These points are pathways for water escape and pose risk on dam’s stability during operation, which mandates a re-grouting program.

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