Investigating Seepage and Stability of Unsaturated Embankment Dams Under Transient Conditions

Evaluation of pore water pressure in conditions of a rapid draw-down of a reservoir water level is one of the most vital issues in the stability embankment dams. The purpose of this study is to investigate seepage flow and slope stability during the rapid draw-down of the reservoir water level for the Doiraj embankment dam. This dam is located in Ilam province, Iran. The finite element method and limit equilibrium method approaches were used. Numerical simulations were carried out for transient unsaturated flows. It is shown that increasing the draw-down decreases the factor of safety. The minimum critical factor of safety decreases with increase in the reservoir water level draw-down rate. This study also reveals that the acceptable water level draw-down rate for this dam could be greater than the recommended water level draw-down rate of the United States Army Corps of Engineers. The critical factor of safety value for the reservoir water level draw-down of 1.20 m/day in the investigated embankment dam was 1.835, which is higher than the minimum standard value of 1.50; hence, the upstream slope is stable even for water level draw-down rates up to this value.