1. Preparations before construction
(1) After HDPE geomembrane enters the site, the appearance must be strictly inspected according to the standard requirements of "High Density Polyethylene Geomembrane for Landfill" (CJ/T234-2006). The quantity and size of the geomembrane shall be witnessed and sampled, and sent to a qualified building material testing center to test the various indicators of the geomembrane such as density, tensile strength, elongation, tear strength, etc. After passing the inspection, it can be used for construction.
(2) Check the completed base layer again to ensure that the surface of the base layer is smooth and free of debris, such as stones, roots, and sharp objects that may damage the geomembrane. There shall be no right-angle rigid structure at the bend of the geomembrane, and shall be made into an arc.
2. Laying of HDPE geomembrane and protective layer Geomembrane laying adopts the order of slope first and then the bottom of the pool. Do not pull too tightly when laying the film, and leave a certain margin for local sinking and stretching. Horizontal joints shall not be on the slope, and shall not be less than 1.5m away from the toe of the slope. The longitudinal joints of two adjacent sheets should not be on a horizontal line, and should be staggered by more than 1m. Do not drag or pull hard during the transportation of the geomembrane to avoid being stabbed by sharp objects. Some temporary air ducts should be pre-laid under the membrane to remove the air under the membrane, so that the geomembrane is close to the base layer. Construction workers need to wear soft-soled rubber shoes or cloth shoes during construction work, and pay attention to the influence of weather and temperature on the membrane.
The specific construction steps are as follows:
(1) Cutting geomembrane: The actual measurement of the laying surface should be carried out to obtain the accurate size, and then cut according to the width and length of the selected HDPE geomembrane and the laying plan, and the lap width should be considered for welding. The corner fan-shaped area of the pool body should be cut reasonably so that the upper and lower ends are firmly anchored.
(2) Detail enhancement treatment: Before the geomembrane is laid, the details such as the yin and yang corners and deformation joints should be strengthened first, and double-layer HDPE geomembrane can be welded if necessary.
(3) Slope laying: The direction of film development should be basically parallel to the slope line, and the film should be flat and straight to avoid wrinkles and ripples. The geomembrane should be anchored at the top of the pool to prevent it from sliding down.
The protective layer on the slope is non-woven geotextile, and its laying speed should be consistent with the film laying speed to avoid artificial damage to the geomembrane. The laying method of the geotextile is similar to that of the geomembrane. The two geotextiles are aligned and aligned. The overlap width is generally about 75mm according to the design requirements, and is sewed and connected by a portable sewing machine.
(4) Laying at the bottom of the pool: The HDPE geomembrane is placed on a flat base, smooth, moderately tight, and closely attached to the soil surface to avoid wrinkles and ripples. The two geomembranes should be aligned and aligned. The overlap width is generally about 100mm according to the design requirements, and the welding parts should be kept clean.
3. Welding and testing of geomembrane
The bonding and welding of geomembrane is the key link to prevent leakage. Hot-melt welding (double-track fusion welding) is often used. It is required that the two geomembranes must be overlapped by more than 100mm before welding.
The specific operation steps are as follows:
(1) Experimental welding. Trial welding shall be performed on HDPE geomembrane specimens and under the same membrane surface and environmental conditions as production welding; experimental welding requires inspection and adjustment of welding equipment; welding equipment and welding personnel are only required to successfully complete the experimental welding Only then can productive welding be performed.
(2) Production welding. First of all, the grease, moisture, dust, garbage and other debris on the surface of HDPE geomembrane should be removed. If there are sundries on the surface of the membrane, the upper and lower membranes cannot be heat-sealed together, which has a great impact on the construction quality. Then adjust the welding machine to the best parameters obtained during the experimental welding, and automatically weld under the condition of the lap width required by the design, and the welding seam is "flat, firm and beautiful". Maintain the welding temperature, speed and pressure of the clamping stick to achieve the best welding effect. Attention should be paid to welding: minimize the welding of side feet and sporadic films; when the ambient temperature and adverse weather conditions seriously affect the welding, the operation should be stopped; if welding at night, sufficient lighting should be ensured.
(3) Weld inspection. The inspection of weld seam is divided into visual inspection, air pressure inspection (non-destructive) and destructive inspection. Visual inspection and air pressure inspection are required for each weld seam, and the qualification rate is required to be 100%. The visual inspection is mainly to carefully check the appearance quality of the weld, the processing of the T-shaped weld and the cross-shaped weld, and the presence or absence of debris at the base. The surface of the weld should be smooth and smooth, with uniform thickness, and there should be no debris and excess solder at the weld, and no damage to the surrounding base metal. Air pressure detection is a non-destructive testing method to judge the quality of welding by checking the air tightness of the weld. The gas with a certain pressure is sealed in the gas chamber, and its air tightness is checked by detecting the change of the pressure gauge attached to the needle.
Destructive testing is to take a 1000mm × 350mm sample for each 1000m weld for strength testing, and the qualification rate is required to be 100%. Defects found in visual inspection and air pressure inspection should be repaired in time, and special marks should be made for those that cannot be repaired immediately to prevent leakage. Holes or pinholes with a diameter of less than 5mm can be spot welded. When the hole is larger than 5mm, apply a 10cm round or oval pad for repair.