Factors to be considered in the design of geomembrane thickness
The selection of composite geomembrane specifications are related to the flatness of the cushion, the allowable tensile stress of the material, the elastic modulus of the material, the maximum water head within the laying range, and the maximum particle size of the covering layer. In addition to the strength required by water pressure, the design of geomembrane thickness should also consider application conditions such as exposure, buried pressure, climate, and service life. The design thickness and actual thickness should be determined according to the current relevant national standards.
In this project, at the upstream dam slope of 369.50m ~ 383.00m, a composite geomembrane of 600 g/m2 with two cloths and one membrane is used for seepage prevention, with a width of 4 m. The composite geomembrane anti-seepage structure consists of a protective layer and a top pad from top to bottom. It is composed of layers, an impermeable layer, an underlying layer, and a support layer. The backfill of the dam body above 369.50 meters above sea level is strongly weathered mud and rock slag. After leveling and tamping, lay a 15cm thick lower sand cushion, then a geomembrane, and then a 15cm thick upper sand cushion and a 15cm thick gravel cushion. Finally, 15cm thick C20 concrete was used for slope protection. the above. The cushion is made of mortar with a thickness of 5 cm, and the protective layer is made of precast concrete slabs with a thickness of 6 cm. The design elevation of the grouting platform is 369.50 cm. After the curtain grouting is completed, a tooth groove with a bottom width of 1.00 meters and a depth of 2.50 meters is excavated on the curtain grouting axis. The geomembrane is directly laid on the bottom of the alveolar, and the clay is backfilled and compacted.
Since the friction coefficient between the composite geomembrane and the earth-rock medium and between the earth-rock medium will affect the stability of the impervious body, the anti-sliding stability of the composite geomembrane and the dam slope, the composite geomembrane and the protective layer must be reviewed.
The connection between the composite geomembrane impervious wall and the rock mass of the dam abutments on both banks should be tight and reliable in accordance with the requirements of the specification, and leave an expansion margin to prevent the composite geomembrane from being damaged due to the settlement of the building. The drainage tunnel is a vertical wall. When the composite geomembrane is connected to the masonry wall, firstly drill holes every 20 cm on the masonry wall, install expansion bolts, install a 5 mm thick and 10 cm wide rubber along the length of the connection, and fold the composite geomembrane into 3 layers, Punch holes and pass through the bolts, and then use a layer of rubber and steel bead to fix the composite geomembrane through expansion bolts. To prevent corrosion of bolts and slats, three layers of anti-rust paint are applied to the bolts and steel slats.