Permeability and groutability appraisal of the Nargesi dam site in Iran based on the secondary permeability index, joint hydraulic aperture and Lugeon tests

Abstract

Seepage from the body and foundations of dams is one of the most important design parameters highly influenced by permeability. Also, permeability is one of the basic parameters for designing grout curtains, preventing water from escaping from the foundation and avoiding negative seepage pressures in borrow materials used for grouting. In this work, rock mass classification of a rock foundation dam site was carried out using the rock mass rating (RMR) and geological strength index (GSI) systems. This study was mainly conducted to evaluate permeability and groutability at the Nargesi dam site in Iran using secondary permeability index (SPI), joint hydraulic aperture (JHA) and Lugeon tests. Also, the dam foundation was evaluated by pressure tests (WPTs) that indicated the need for a grout curtain below the dam foundation. The rock mass quality of the samples obtained via the SPI in conjunction with the drill core jointing degree acts as a useful reference for ground treatment design. The dam foundation groutability was zoned according to an SPI classification point view. There is no direct relationship between the JHA values and water take in all the sections, but a direct relation is observed in some boreholes. Such a relationship can be attributed to joint characteristics such as persistence, etc. The results of this work revealed, except for a few cases, there is a reasonable correlation between secondary permeability index (SPI) and rock quality designation (RQD) values. Based on these results, a grout type and composition was suggested for construction of the grout curtain.