Principle of Geotextile for Reservoir Seepage Prevention
Barrier Function: The seepage - proof base materials such as plastic films in geotextiles, like polyvinyl chloride (PVC) and polyethylene (PE), are impermeable. They can effectively block the leakage channels between the reservoir water body and the underlying soil, preventing water seepage.
Reinforcement Function: Geotextiles themselves have high tensile strength and extensibility. When combined with plastic films, not only do they increase the tensile strength and puncture - resistance of the plastic films, but they can also withstand water pressure and adapt to the deformation of the reservoir dam body.
Filtration Function: The fiber structure of geotextiles forms a net - like structure. The mesh holes are not easily blocked, and it has good water conductivity. It can allow water to pass through while effectively retaining sand and soil, preventing the loss of sand and soil, playing the role of filtration and isolation, and ensuring the stability of the reservoir slopes and bottom.
Application Positions of Geotextiles in Reservoirs
Reservoir Bottom Lining: Laid at the bottom of the reservoir, it is a key defense line to prevent reservoir water from seeping into the ground. It can effectively maintain the water storage capacity of the reservoir and reduce water waste.
Slope Protection: Covered on the reservoir slopes, it can prevent soil erosion caused by rainwater scouring. At the same time, it can also prevent the water in the slope soil from seeping out, avoiding unstable phenomena such as landslides due to changes in soil moisture content.
Cofferdam Construction: In the cofferdam construction during the construction or maintenance of the reservoir, geotextiles can be used as seepage - proof materials to prevent the exchange of water inside and outside the cofferdam, providing a dry working environment for the construction inside the cofferdam and ensuring the smooth progress of the construction.
Construction Key Points of Geotextile for Reservoir Seepage Prevention
Preparation of Construction Base Surface: Ensure that the base is flat, the base is dense and uniform, the base surface has no sharp objects, no seepage, no silt, no water accumulation, and the base surface within the surrounding anchor line range is smooth. Remove sundries such as tree roots, oversized angular stones, steel bar heads, steel wires, and glass chips within the laying range, which may damage the geotextile.
Laying of Geotextile: Geotextiles should be laid under suitable weather conditions, such as when the air temperature is above 5 degrees Celsius, the film temperature is above 20 degrees Celsius, the wind force is below level 4, and there is no rain or snow, in a dry and warm weather. When laying, it should be extended from the bottom to a high position. Do not pull it too tightly, and leave a certain amount of extra width to prepare for local subsidence and stretching. The longitudinal joints of two adjacent pieces should not be on the same horizontal line. They should be staggered by a certain distance. The longitudinal joints should be at a certain distance from the dam toe and the bend, and should be set on a flat surface.
Welding and Connection: The connection between geotextiles usually adopts welding methods, such as hot - wedge, heat - fusion, extrusion, and hot - melt welding methods. Before welding, a small - sample strip welding test should be carried out according to the on - site climate conditions to determine the formal welding parameters. During the welding process, pay attention to controlling parameters such as welding temperature, pressure, and speed to ensure the quality of the weld. For the repair of geotextiles, appropriate methods should also be used for hot - melt bonding and testing.
Construction of Anchor Structure: The anchoring of the peripheral structure of the geotextile is an important part to ensure the seepage - proof effect. Anchor holes are usually drilled by a drilling machine. Then, chemical anchor agents are used to fix the bolts, and nuts are used to fix and reinforce the angle steel and bolts. Before construction, clean and trim the foundation surface. After the anchor holes are formed, keep the holes clean. After the anchor agent is cured, repeatedly tighten the nuts until the tightening force meets the design requirements.
Quality Inspection of Geotextile for Reservoir Seepage Prevention
Visual Inspection: Conduct a comprehensive inspection of the laid geotextile. Observe whether the geotextile is laid flat, whether there are wrinkles, damages, holes and other defects, whether the welds are uniform and continuous, and whether there are cases of missed welding or false welding. For the detected quality defects or suspicious parts, mark them with colored pens of different colors and record them in detail.
Inflation Detection: Inflate the welds of the geotextile to detect the tightness of the welds. When the inflation pressure reaches a certain standard, such as 0.2 MPa, and after maintaining it for 5 minutes, if the pressure does not drop significantly, the weld is qualified. The pinholes left by the inflation detection must be sealed and then subjected to vacuum testing.
Vacuum Detection: Use a vacuum hood to test the welds of the geotextile. When the negative pressure reaches below 0.02 MPa and is maintained for 30 seconds, if the pointer of the pressure gauge does not drop significantly and no soap bubbles are generated on the weld, it is qualified. The detection range should be smaller than the diameter of the vacuum hood. At the same time, the sealing liquid applied around the vacuum hood should not cause corrosion and damage to the geotextile.
Peripheral Leakage Detection: For the peripheral anchor structure of the geotextile, use a sealed seepage detection box for detection. Add water to the detection box and pressurize it to the maximum water head that the film can bear. Stabilize the pressure for 8 hours. If the water pressure does not decrease, it indicates that the quality of the anchor structure is qualified. During the detection process, pay attention to slow pressurization and exhaust the air in the box. Once water seepage is found around the box, stop pressurization immediately, check the cause of the water seepage, and conduct the detection again.
