For earth rock dams with geomembrane for seepage control, the general circular slip surface or broken line sliding surface is adopted for the dam slope. After calculation, the anti sliding stability of the contact surface between the inclined geomembrane and its adjacent soil and stone materials should be calculated, that is, the plane sliding stability between the geomembrane and the upper protective layer, and between the geomembrane and the underlying cushion.

 

Because the friction coefficient between geomembrane and soil, sand and pebble is less than that of soil and stone, the friction coefficient between the outer layer of composite geomembrane and earth rock is also smaller.

 

In addition. If the membrane of composite geomembrane and geotextile are not hot pressed or bonded together, the friction coefficient between the membrane and geotextile is smaller.

 

For the sake of stability, the membrane and cloth should be hot pressed or pasted together. When the geomembrane is laid on the slope of permeable material dam, the dangerous sliding surface is between the upper protective layer and the lower cushion layer, and the possibility of sliding between the geomembrane or geotextile and the underlying cushion is not very likely, because the rockfill dam has strong water permeability, and there will be no water retention between the geomembrane and the cushion.

 

Discussion on impervious layer of Geomembrane

 

1. The leakage of composite geomembrane is very small, and a small amount of water loss in water conservancy project will not affect the normal benefit. Therefore, the calculation of leakage is not a key problem. However, for toxic liquids, especially highly toxic liquids, a very small leakage basin is very harmful, so it is necessary to calculate the leakage disc. In addition, some measures should be taken from the structure of the anti-seepage layer, such as the use of double-layer geomembrane impervious layer, so as to ensure that the leakage can be reduced to the standard level.

 

2. The influence of defect size on the leakage of single-layer geomembrane impervious layer is quite obvious, while that of composite impervious layer is less. Therefore, in order to reduce the leakage of defects, the effect of composite anti-seepage layer is obviously better than that of single-layer geomembrane.

 

3. With the increase, it is basically linear. However, the thickness of the soil layer has little influence on the defect leakage basin, which indicates that the low permeability soil layer under the geomembrane need not be too thick. It is mainly determined by the factors such as the distribution of soil materials and the construction conditions. Therefore, the low permeability soil should be selected as far as possible.