عدي عبد الصاحب محمد حسن الطرفي

Gravity Dams depend mainly on its own mass to resist the effecting uplift pressure. The effect of uplift pressure can be reduced by using a drainage gallery. The optimum position of the drainage gallery under gravity dam results maximum drain reduction factor. in this study, numerical method (two dimensional finite element) are used to analyze hydraulics of uplift pressure under the gravity dam and its effect on usage of gallery drain, and without gallery drain for different reservoir and drain location along the base of the dam. Two models used once without sheet pile and another with sheet pile. drain reduction factor (DRF) had been calculated to demonstrate the effect of used gallery drain in the system. the results indicate that the gallery drain nearest the upstream side close to Xd/B=0.167 results in maximum (DRF) close to 0.494, and can be achieved as the optimum position of the drainage gallery, at which seepage discharge entering the drainage gallery is maximum. The results of comparison between the two models showed that the usage of gallery drain and sheet pile in the system reduces the uplift force more than 40% and 20% respectively. The analysis process depends on computer program package “SLIDE V.5.005”.