The water–air two-phase unsaturated seepage theory was employed to analyse the transient seepage field of an earth-rock dam with an impervious geomembrane barrier during rapid drawdown of the reservoir. Discussed is the resulting seepage behaviour of the dam after locations of defects in geomembranes and hydraulic conductivity of dam materials were changed. In addition, the unsaturated soil strength theory was used to calculate the anti-sliding safety factor of the upstream dam slope during drawdown. The uncertainty of effective stress parameters of dam materials was considered, and the Monte Carlo method was employed in the reliability analysis of the stability of the upstream dam slope. The results indicate that the location of defects has a significant influence on the initial phreatic surface distribution and the seepage flux mainly depends on the hydraulic conductivity of dam materials. Geomembranes with defects on the dam surface have an apparent hysteresis effect on the descending of the phreatic surface when the reservoir level drops, which causes a great decrease in the stability of the upstream dam slope. Matric suction significantly affects the stability of the upstream dam slope, while the air phase has little effect on slope stability when geomembranes are placed on the upstream surface of the dam.

中文翻译：

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瞬态渗流对具有土工膜屏障缺陷的土石坝边坡稳定性的影响

利用水-气两相非饱和渗流理论，对水库快速降落时土工膜不透水的土石坝瞬态渗流场进行了分析。讨论的是在土工膜中的缺陷位置和大坝材料的水力传导率发生变化后，大坝的渗漏行为。另外，利用非饱和土强度理论计算了上游坝坡降坡时的抗滑安全系数。考虑大坝材料有效应力参数的不确定性，采用蒙特卡罗方法对上游大坝边坡的稳定性进行可靠度分析。结果表明，缺陷的位置对初始潜水面的分布有很大的影响，渗流主要取决于坝体的水力传导率。当水库水位下降时，在坝面有缺陷的土工膜对潜水面的下降具有明显的滞后作用，这会导致上游坝坡的稳定性大大降低。矩阵吸力显着影响上游大坝边坡的稳定性，而当将土工膜放在大坝的上游表面时，空气相对边坡稳定性的影响很小。这导致上游大坝坡度的稳定性大大降低。矩阵吸力显着影响上游大坝坡度的稳定性，而当土工膜置于大坝上游表面时，空气相对边坡稳定性的影响很小。这导致上游大坝坡度的稳定性大大降低。矩阵吸力显着影响上游大坝坡度的稳定性，而当土工膜置于大坝上游表面时，空气相对边坡稳定性的影响很小。