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Earth dams control and store river water. Type of the earth dam is selected on the basis of available borrow sources. Where it is not possible to have access to suitable fine-grained sources for constructing an earth dam, then using homogeneous materials and an impermeable blanket is recommended. In this research, a mixture of sandy soil with 0.25, 0.5, 0.75, and 1 wt% of montmorillonite nano-clay was used to make the impermeable blanket. After initial tests of gradation, permeability, and optimum moisture content on the soils, experimental models of homogeneous earth dam with an impermeable blanket were constructed. The time needed to reach the steady-state phreatic line and seepage discharge in the models was compared in transient and unsaturated cases. Results showed that increasing the amount of nano-clay from 0.25 to 1.0%, decreased seepage discharge by 19, 67, 89, and 97 …