Phreatic Surface Calculation and Stability Analysis of Three-Dimensional Bank Slopes with Reservoir Drawdown

Among all factors affecting the stability of soil slopes, the effects of seepage, and especially drawdown, have long been a topic of study. This paper proposed a novel method for predicting the phreatic surface of three-dimensional (3D) slopes. Based on the solved phreatic surface, the normal stress expression of the slip surface under seepage force was deduced. A strict overall analysis method that combines the seepage force to analyze the stability of the bank slopes with reservoir drawdown was proposed. The credibility of the proposed method was verified by calculating different conditions set by a classic slope model. Finally, the change rules of the phreatic surface and the safety evolution with reservoir drawdown of a practical slope in the Three Gorges reservoir area were studied. The results demonstrated that the safety factor of the slope first decreases and then increases with reservoir drawdown and the most unfavorable water level is at the lower 1/3–1/4 of the total height of the slope.