Geomembrane design

The composite geomembrane anti-seepage core structure consists of four layers: foundation, composite geomembrane, protective layer, and block stone (or concrete) slope protection. The design of each layer is described as follows:
Base design
In order to prevent the sliding of the filling layer on the composite geomembrane along its surface and increase the stability of the protective layer (including the protective surface), the upstream membrane dam shell surface is excavated into a platform stage, with a height difference of 0.3m for each stage. The horizontal width is determined based on the slope ratio, and the slope design is 1:1.0. After excavation, the bricks, stones, and * root trees on the surface are cleaned, and the surface is compacted and leveled with clappers.
Composite design
Based on the main characteristics of the product and the specific situation of Zhoutou Reservoir, WCD-1 type two cloth one membrane composite geomembrane is designed and selected.
Protection design
The anti-seepage effect of composite geomembranes depends on the integrity of the plastic film during construction and operation. In order to prevent human and animal trampling, damage to animals and plants, and reduce photothermal effects, as they are polymer fibers, direct sunlight should be particularly avoided. Therefore, a protective layer should be laid on the composite geomembrane.
The particle diameter of the protective layer should not be too large, otherwise it will puncture the composite geomembrane. Generally, the particle diameter of the protective layer should be estimated approximately according to the following equation.
In the formula: d - the maximum particle diameter of the protective layer soil material;
K - safety factor, k=5 for this project;
[ σ]-- Allowable tensile strength of composite geomembrane[ σ]= 5.5Mpa;
P - Maximum water head, taken as P=0.1Mpa;
--The thickness of composite geomembrane is taken as 0.2mm (plastic film thickness).
Substitute the above data into the above equation to obtain:
For safety reasons, it is required that the actual maximum particle diameter d of the soil material should not be greater than 6mm. Therefore, this project uses screened silty clay, and other requirements are the same as the requirements for filling the dam body soil material. The protective layer is taken as 200mm, with 100mm of screened soil below and 100mm of non screened soil above. For non screened soil, larger stones and other debris should be picked out.
Face protection design
Because the dam slope is a water retaining structure that needs to withstand wind and wave pressure, it is necessary to have protective measures. The design of this project adopts dry masonry large stone protective surface.
The protective stones must be hard, dense, able to withstand long-term weathering, and have a certain amount of weight, capable of withstanding the effects of wind, wave pressure, and water erosion.
The weight, Q, and thickness of the protective stone are determined by referring to Appendix D.3 of the "Design Code for Embankment Engineering" GB50286-98. Calculation formula:
In the formula: Q - Individual mass of the main protective layer protective stone (t)
Rb - Unit weight of artificial block stone (KN/m3) rb=24KN/m3
R - weight of water r=10KN/m3
H - Design slope height H=
KD - Stability coefficient, KD=5.5
T - Thickness of block stone protective layer
N - Number of protective stone layers n=1
C - coefficient c=1.4
M - Slope gradient
After calculation, Q=48kg, t=0.29m, and the thickness of dry block stone cover t=0.3m.