The impermeable structure of the composite geomembrane consists of four layers: the base surface, the composite geomembrane, the protective layer, and the riprap (or concrete) slope protection. The design of each layer is described as follows:
① Base Surface Design (i.e., requirements for dam shell surface treatment)
To prevent the soil layer laid on top of the composite geomembrane from sliding along its surface, and to increase the stability of the protective layer (including the slope protection), the upstream dam shell surface where the geomembrane will be laid is excavated into terraces. Each level has a height difference of 0.3m, and the horizontal width is determined according to the slope ratio. The designed slope is 1:1.0. After excavation, all bricks, stones, tree roots, etc., are removed from the surface, and the surface is compacted and leveled with a tamper.
② Composite Geomembrane Design
Based on the product's main characteristics and the specific conditions of the Zhou Tou Reservoir, the WCD-1 type composite geomembrane with two fabrics and one film is selected for design use.
③ Protective Layer Design
The impermeability effect of the composite geomembrane depends on the integrity of the plastic film during construction and operation. To prevent trampling by humans and animals, damage by plants and animals, and reduce the effects of light and heat (as they are high molecular fiber polymer materials), direct sunlight should be particularly avoided. Therefore, a protective layer should be laid on top of the composite geomembrane.
The particle diameter of the protective layer cannot be too large, otherwise it may puncture the composite geomembrane. Generally, the particle size of the protective layer is estimated using the following formula.
④ Slope Protection Design
Since the dam slope is a water-retaining structure that must withstand wind and wave pressure, slope protection measures are necessary. This project uses dry-laid large stone slope protection.
The slope protection stones must be hard, dense, able to withstand long-term weathering, and have sufficient individual weight to withstand wind and wave pressure and water flow scouring.
To prevent wind and water flow from carrying away the clay particles of the dam shell protective layer, a 0.1m thick layer of crushed stone (gravel) is laid under the stone slope protection as a cushion and filter layer.
For purchasing high-quality geotextile membrane, composite geotextile membrane, impermeable membrane, and geotextile fabric, please visit Shandong Xin Zhi Geosynthetic Materials Co., Ltd. at http://www.sdxinzhi.com/.