Study of the effect of seepage through the body of earth dam on its stability by predicting the affecting hydraulic factors using models of Brooks-Corey and van Genuchten (Case study of Nazluchay and Shahrchay earth dams)

Stability of an earth dam is affected by different factors of which the most important is seepage. One of the factors in defining the seepage rate is hydraulic conductivity coefficients in suctions and various moistures in earth dam body in which different models of soil-water retention curves are used to be defined. In this study, first the soil-water retention curves of van Genuchten and Brooks-Corey models are used to predict the soil-water retention of different body layers of 2 dams. Then, hydraulic conductivity coefficients are calculated through Mualem and Burdine's models. Water seepage rate and the stability of dams were calculated in two phases: I. construction finalization prior to intaking water and II. rapid drawdown of water. Bishop and Morgenstern-Price methods are used to analyze the stability of dams. The stability and seepage results demonstrate that simultaneous use of Brooks-Corey's soil-water retention curve with Mualem's method results in the highest seepage rate in comparison with van Genuchten's model in case of variable n, m and Burdine hydraulic conductivity. Safety factors achieved from both cases of construction finalization prior to intaking water and rapid drawdown of water demonstrated the accuracy and reliability of hydraulic coefficient prediction.