Gypsies soils are often found in arid and semiarid zones where leaching process of the gypsum from the soil cover is insufficient by the rainfall. The dissolution of gypsum salts causing caves, increasing the permeability of soil materials, increases of flow rate due to enlarging fissures and causing excessive settlements, all these causes reduce the efficiency of dams impounding water. The main aim of this work is to understand the behavior of earthfill dams and check stability if the gypsum materials are found in the construction materials of the body of the earthfill dam. Seven experimental models of earthfill dams are constructed in a laboratory drainage and seepage tank. The dimensions of models are same to fit the space of the tank but different in percentage of gypsum, 0%, 1%, 2%, 3%, 4%, 5%, and 10%. For each model, results are obtained for location of seepage line, the variation of seepage flow rate and gypsum dissolution rate with time, and slopes failure during operation and at sudden drawdown. Increasing gypsum content increases the seepage flow due to the enlargement of the voids caused by the disintegration of the soil by gypsum dissolution. Slopes failure occur at gypsum ≥ 4%, therefore one can say earth material with gypsum ≤ 3% are suitable for construction of earthfill dams.
Keywords: Stability, Earthfill, Dams, Dissolution, Gypsum.