Evaluation of permeability and groutability of quaternary deposits and sedimentary rock masses at Nargesi damsite

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 water reserves. For this purpose, studies are done about permeability of the rocks mass damsite and the sealing methods. Moreover, seepage of Nargesi dam is discussed as a case study in this article. Based on the geological studies, Nargesi dam is located on the quaternary deposits and sedimentary formations that include; Bakhtiary, Mishan and Gachsaran. Water seepage was evaluated according to the water pressure tests (lufrance and Lugeon) on quaternary deposits and sedimentary formations where outcrops in the left and right abutments. The secondary permeability index (SPI) introduced by Foyo et al (2005) for investigate effect rocks jointing characterization in its permeability. The key point of this method is the fact that it allows distinguishing the difference between dilation and hydraulic fracturing. Permeability of the rock masses interpreted based on SPI considering the result of Lugeon tests and the drilled core properties. Also, Permeability and rock quality designation zonation according to effective engineering geological properties was dawn with Rockwork 14 software. Finally suitable profiles were presented 3 dimensional view and comfortable engineering verdicts. 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 left abutment and Mishan formation has better situation as compared to Gachsaran and Bakhtiary formations from view point of permeability.