Defect-induced leakage of geomembranes may have negative effect on the anti-seepage safety of geomembrane faced earth-rock dams. Finite element theory of saturated-unsaturated seepage was employed for the 3D simulation of the seepage field of a typical geomembrane faced earth-rock dam in the condition that defects are in random distribution on the upstream dam surface. The quantity, types, location, sizes and distribution of geomembrane defects were considered reasonably, and the change rules of infiltration capacity, defect-induced leakage and phreatic line were analyzed emphatically. The results indicate that in the condition that the geomembrane is intact, the seepage flux changes little for both single and multiple defects on the geomembrane. However, when the geomembrane is under multiple defects, the defect-induced leakage increases significantly,leading to the increase of total seepage flux. Multiple defects will raise the phreatic surface in the dam body,and the variation of local phreatic surface height is related to the quantity and location of the defects. The more and lower the defects are, the more obvious the uplift of the phreatic surface can be. Further, the local distribution of water head behind the geomembrane is related to the cross effect of leakage of adjacent defects.%由于土工膜缺陷渗漏可能对土工膜防渗土石坝的防渗安全性造成隐患,采用饱和-非饱和渗流有限元理论,对坝面防渗土工膜多缺陷随机分布下的典型土石坝进行三维渗流场有限元模拟,合理考虑土工膜缺陷的数量、类型、位置、大小及其分布,重点分析土工膜的渗透量和缺陷渗漏量及膜后浸润面的变化规律.结果表明:与单缺陷条件下大坝渗流特性相比,坝面完好部分土工膜的渗透量变化不大,但多缺陷引起的渗漏量明显增大,导致大坝的总渗流量大幅增加.多缺陷会引起膜后坝体浸润面整体抬升,但局部浸润面高度变化与缺陷位置和数量明显相关,所在剖面缺陷位置越低,数量越多,浸润面抬升越明显.另外,膜后垫层水头局部分布规律与相邻缺陷渗漏的交叉效应相关.
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