In order to facilitate calculation, the thickness of hdpe geomembrane pond liner is magnified 100 times according to the principle of equivalent amplification of permeability coefficient. The upper and lower reaches of the model were cut twice the dam height, and 7.2m below the bottom of the cut-off wall was taken as the bottom boundary. After the model is discrete, the number of nodes is 7652, and the number of elements is 14872. During calculation, the bottom and upstream and downstream boundaries of the model were set as impervious boundaries, the upstream dam slope below the normal storage level was set as the known head boundary, and the downstream dam slope was set as the escape boundary.
The permeability coefficient at the defect damage should be infinite. Considering the small permeability coefficient of geomemes, the permeability coefficient is set as 100m/s. With the increase of water head and defect size, seepage factors such as seepage slope and seepage flow rate of single width gradually increase, while seepage slope and seepage flow rate of single width at the bottom of seepage wall of dam foundation gradually decrease. When the defect size is less than 0.2m, the lower defect has the greatest influence on the seepage factors at the bottom of the dam body and dam foundation cut-off wall, followed by the middle defect, and the upper defect has the least influence. When the defect size reaches 0.2m, the central defect has the greatest influence on the seepage factors at the bottom of the dam body and dam foundation seepage wall, followed by the lower defect, and the upper defect has the least influence.