Seepage and Stability Analysis of the Eyvashan Earth Dam under Drawdown Conditions

The rapid drawdown condition to control floods and irrigation is one of the things that may occur over the lifetime of the dam. Also, the stability of the dam at the rapid drawdown will be more important due to the faster reduction of the water level of the dam reservoir than the pore water pressure. In this study, the finite element method and GeoStudio software used to study the seepage from the body earth dam. Also, the complete elastic-plastic model of Mohr-Coulomb is considered in the analysis. In this study, the stability analysis of the Eyvshvan earth dam after rapid drawdown due water to release of the dam reservoir to downstream agricultural lands during drought crisis, is investigated. For the validation, first, the results of the pore water pressure instrument were compared with the results of numerical analysis. The results of multivariate regression analysis (coefficient of determination) showed very good agreement (R-2=0.98). The results showed that the phreatic line remains after 29 days from the start of the rapid drawdown of the reservoir, while half of the volume of the drained reservoir remains at 1842 masl (1/3 of the crest). The analysis of dam stability during rapid drawdown using both Morgenstern-Price and Bishop Methods showed that the most critical situation would occur after 42 days of discharge with a factor of safety (FoS) of 1.71, with no stability hazard and the upstream slope would be safe.