The canal seepage control is currently the most widely used water-saving irrigation engineering measures, it can greatly reduce the waste of agricultural irrigation water channel anti-seepage measures, can improve the water use efficiency, ease the contradiction between supply and demand of agricultural water saving, water can expand the irrigated area, to further promote the development of agricultural production can reduce the channel area; the channel, to prevent erosion and siltation and collapse, saving the cost of operation and management, is conducive to irrigation management; can reduce the ground water level and prevent soil salinization and swamping, conducive to the ecological environment and agricultural modernization. Canal Anti-seepage is an important part of saving water and realizing water-saving agriculture. Seepage control of canal can be made of impervious soil, impervious to cement soil, impervious to stone masonry, impervious to concrete, impermeable to impervious membrane and impervious to bituminous concrete. The main HDPE high density polyethylene geomembrane geomembrane widely used seepage control. It is a kind of polymer chemistry of flexible material, extensibility, high deformability, corrosion resistance, low temperature resistance, frost resistance. With the development of science and technology, has become an important measure of seepage control of Canal Anti-seepage by impermeable membrane.
1, the aging of impermeable membrane
The membrane is made of polymer materials by processing them in transportation and construction and in the long run period will change due to various causes, the performance deterioration and aging; aging of materials has several manifestations: the appearance of surface cracks, discoloration and embrittlement, loss of gloss, mechanical performance decline, the biggest impact on the project the decline of the mechanical properties, such as tensile strength and failure strain of the material decreased, directly affect the channel leakage, affecting the normal operation of the channel.
Light decay and oxidation decay caused by ultraviolet radiation is the main influencing factors of impervious membrane aging, solar radiation to the earth's atmosphere of light is a continuous spectrum, ultraviolet rays reach the earth's surface will cause light oxygen material aging, thermal aging caused by temperature and oxygen, their total energy is obviously higher than that of impermeable membrane some chemical bond that caused membrane aging.
In the process of using, the material is exposed, the oxygen supply is high, the sunlight is stronger, and the decay is faster than that concealed. To this end, both in storage and transportation, construction and long-term operation, the material should be protected. The most basic requirement is that after the material is laid, it should be covered with soil as soon as possible, the thickness is not less than 30 cm; the material is covered with water under the water, and the aging decay will also decrease.
2, the thickness of the impermeable membrane
Technical specification for water conservancy and Hydropower Engineering Application of geotechnical synthetic materials (SL/T225 98) the provisions of article 5.3.2: dams and impermeable impermeable membrane thickness should not be less than 0.5mm, for the important projects should be properly thickened; for minor works, can be properly reduced, the smallest not thinner than 0.3 mm. The impervious membrane is sensitive to concentrated stress and easily punctured. The impact resistance of the film increases with the increase of the film thickness; the film is too thin and the impermeable film is easily damaged during hot melt welding. In order to ensure the quality of the project, it is recommended to check the thickness of the impermeable membrane strictly.
3. Welding of impervious membrane
There are two kinds of splicing of impermeable membrane: adhesive method and hot-melt welding machine, welding method of two. In the two film adhesive method is coated with adhesive, and then pressing adhesive bonding agent can make the surface of emulsion membrane, after bonding with the volatile solvent and the contact surface with dry adhesive; the choice is very important, such as PVC film can be PVC rubber or polyurethane glue adhesive; polyethylene film KS hot melt adhesive bonding. In general, the joint strength of bonding method is less than that of hot welding machine, and the degree of automation is low. It is often because of human factors that leakage occurs. Twin track hot melt welding is the most widely used hot melt welding method. The temperature setting of the hot melt welding machine is recommended to be 225-400 degrees (adjusted according to the thickness of the impermeable film), and the welding test can be done first to obtain an ideal welding speed. In addition, weather factors, such as temperature, sunshine and wind speed, can affect the quality of welding. Therefore, the above factors should be taken into account when setting up welding conditions. Then install the two overlapped impervious membrane into the wedge and the roller, the driving motor must be closed in advance to the point positioning, impermeable membrane embedded in the roller, immediately start the motor and lock the welding parts. The welding personnel shall pay attention to the welding speed, the actual welding temperature and the straightness of the welded track at all times so as to achieve uniform welding quality. When welding on the welding track there will be a small amount of melt extrusion (Squeeze-Out), said to the appropriate welding temperature, when the extrudate appears excessive, said the welding temperature is set too high or roller pressure is too large, need to be adjusted. If the use of embossing roller welding machine, the welding parts (track) shall be visually to the embossing wheel tread, hand to check, only we have touch. Welding machine shall be checked and repaired every day after welding.
4, the laying of impermeable membrane
From construction technology, the core problem of membrane seepage prevention construction quality, integrity of the canal remained impervious membrane in the construction process of the film laying trench excavation leveling, leveling process first at the ditch stones and other sharp objects, and then processed into a film according to the channel size, from downstream to upstream channel. From a bank to another bank channel laying membrane membrane laying, don't pull too tight, should be a small fold, and flat channel base, air impermeable membrane should be completely eliminated from the gravel layer, due to membrane surface transition layer with protective layer in laying gravel gradation requirements when layer compaction. Rigid material protection layer, should prevent the rigid material through the impermeable membrane, otherwise it will