Anti-seepage construction scheme of HDPE membrane in landfill
Before laying HDPE geomembrane, a comprehensive inspection of the laying base should be carried out in conjunction with the civil engineer, the supervisor, the design, and the owner, and the construction can be carried out after meeting the design requirements and construction conditions, and making a handover inspection record.
Chapter 1, base surface requirements
1. Before laying HDPE geomembrane, a comprehensive inspection of the laying base should be carried out in conjunction with the civil engineer, the supervisor, the design, and the owner, and the construction can be carried out after meeting the design requirements and construction conditions, and making a handover inspection record.
2. The quality of the base surface should meet the design requirements: the bottom surface of the foundation pit, the slope surface and its slope ratio, the anchoring groove on the slope, the treatment of the junction of the slope surface and the righteous surface, and the base surface of the warehouse wall concrete structure should strictly meet the design requirements.
3. The base surface should be dry, compacted, flat, no cracks, no obvious sharp protrusions, no mud, no depressions, and there should be tree roots, rubble, stones, steel bars, and glass chips inside the vertical depth of 25mm. The flatness should change gently within the allowable range, the slope should be uniform, and the slope should be consistent.
4. The shadows at the yin and yang corners on the base surface should have a smooth transition, and the root of the column should be made into an arc shape.
5. The surface of the substrate should be dry, and the moisture content should be below 15%.
6. The base should be dense and uniform, and the dry density of the soil base should not be less than 1.4t/㎡.
7. Geomembrane construction can be carried out after the civil engineering, supervision, design unit, owner, and general contractor have signed and approved it.
Chapter 2. Climatic requirements for construction
1. The temperature should generally be above 5 degrees Celsius, the geomembrane should be tighter at low temperature, and the geomembrane should be relaxed at high temperature.
2. The wind is below level 4.
3. When the temperature is too low, the construction should generally not be carried out in strong winds above level 4 and in rainy and snowy weather.
4. In windy weather, when the wind affects the construction of the geomembrane, the HDPE geomembrane to be welded should be firmly pressed with sand bags.
Chapter 3. Laying of HDPE Shop
1. Before laying HDPE geomembrane, the corresponding acceptance certificate of civil engineering should be obtained.
2. Before the HDPE film is cut, its relevant dimensions should be accurately measured, and then cut according to the actual size. Generally, it is not suitable to cut according to the size shown in the figure. It should be numbered one by one and recorded in detail on a special form.
3. When laying HDPE geomembrane, the minimum number of welds should be sought, and raw materials should be saved as much as possible under the premise of ensuring quality. At the same time, it is easy to guarantee the quality.
4. The lap width of the seam between the film and the film is generally not less than 10cm, and the welding seam is usually arranged parallel to the maximum slope, that is, along the slope direction.
5. Usually in corners and deformed areas, the length of the seam should be shortened as much as possible. Except for special requirements, on slopes with a slope greater than 1:6, within 1.5 meters from the top slope or the stress concentration area, no welds should be provided as much as possible.
6. During the laying of HDPE geomembrane, artificial folds should be avoided. When the temperature is low, it should be tightened as much as possible and paved.
7. After the HDPE geomembrane is laid, walking on the membrane surface, moving tools, etc. should be minimized. Any objects that can cause harm to the HDPE membrane should not be placed on the membrane or carried on the membrane to avoid damage to the membrane. cause accidental damage.
Chapter 4. Welding of Geomembrane
1. The welding process of the hot wedge welding machine is divided into: adjusting the pressure, setting the temperature, setting the speed, welding seam lap inspection, loading the film into the machine, starting the motor, and pressure welding.
2. There should be no oil stains and dust at the joints, and the lap surface of the HDPE geomembrane should not be trapped with debris such as sediment. When there are debris, it must be cleaned up before welding.
3. At the beginning of welding every day, a 0.9mm × 0.3mm sample must be tested on the spot, and the lap width is not less than 10cm, and the peeling and shearing tests are carried out on-site with a tensile machine. After the sample is qualified, it can be adjusted at that time. Good speed, pressure, and temperature are just welding. The date, time and ambient temperature should be marked on the sample. During the welding process of the hot wedge welding machine, attention should be paid to the operation of the welding machine at any time, and the speed and temperature should be fine-tuned according to the actual situation on site.
4. The welding seam is required to be neat and beautiful, and there should be no slip welding and skipping phenomenon.
5. When the length of the geomembrane is not enough, it needs to be spliced in the long direction. The transverse welds should be welded first, and then the longitudinal seams should be welded. The transverse welds should be in a T shape with a distance of more than 50cm, and should not cross.
6. The adjacent geomembrane welds should be staggered and overlapped as much as possible. The joints formed between the membrane blocks should be T-shaped, and cross-shaped should be minimized. The intersection of the longitudinal mold and the weld should be strengthened by an extrusion welder.
7. When welding the film, it is not allowed to press out the dead break. When laying the HDPE geomembrane, according to the local temperature change range and the performance requirements of the HDPE geomembrane, reserve the expansion and contraction amount caused by the temperature change.
8. When the temperature of the welding machine indicated by the temperature control of the portable welding machine is lower than 200 ℃, it should be wiped off with a clean cloth or cotton yarn before welding. If necessary, it should be re-polished.
9. When the joints are affected by condensation, moisture, sediment, etc., weld them after treatment.
10. Welding cannot be performed during rain or when the joints have moisture, dew, or heavy sand, unless protective measures are taken.
11. When the temperature is lower than 5℃, construction should not be carried out according to the requirements of the specification. If construction is necessary, the welding machine should be preheated before welding.
12. During the welding process of the extrusion welding machine, the slider of the gun head should be checked frequently. When the wear is serious, the slider should be replaced in time to avoid damage to the film surface.
13. The geomembrane should be powered by a generator with good voltage stabilization performance during welding, and a voltage stabilizer must be used when using local electricity in special circumstances.
Chapter 5. Anchoring of HDPE film
1. There are three methods of anchoring: groove anchoring, nail anchoring and expansion bolt anchoring; usually, groove anchoring is used.
2. When using trench anchoring, the width of the anchoring trench is generally not less than 0.5m-1.0m, and its depth is not less than 0.5m-1.0m, depending on the use conditions and stress conditions of the HDPE geomembrane.
3. When using nails for anchoring, the width of the bead should not be less than 2cm, the thickness should not be less than 2mm, the distance between the nails should not be greater than 400mm, and anti-corrosion measures should be taken in the exposed areas of the bead.
4. When using expansion bolts for anchoring, the diameter of the bolts should not be less than 4mm, and the spacing should not be greater than 0.5mm. During construction, first use prepared sandbags to temporarily fix the film in place to prevent the HDPE film from being blown and displaced by strong winds. Carry out expansion bolt anchoring.
Chapter 6. Precautions for construction of geomembrane
1. Electrical equipment and power lines should meet the requirements of relevant professional specifications.
2. The power cords towed by the hot air gun, grinder and welding machine must be kept as far away as possible from their working parts during use, so as to avoid damage to the brain wires and leakage of electricity.
3. Except for hot air welding, the mouth of the hot air gun must not be in contact with the HDPE film surface under any circumstances, and should be kept as far away as possible from the film surface, human body, machinery and other objects.
4. When the welding machine is not in use, it should not be placed directly on the HDPE film surface, but should be placed on the bracket or sandbag belt.
5. After the film cutting knife is used, the blade should be immediately returned to the knife box.
6. All kinds of temporary small tools used on site should be put into the toolbox in time after use.
7. It is strictly forbidden to directly discard the solder material removed from the torch head of the extrusion welding machine on the surface of the geomembrane.
8. Safety belts and helmets must be worn when working in dangerous places such as the edge of a steep slope.
9. Smoking is prohibited at the construction site of HDPE geomembrane, and firefighting facilities should also be provided. Shoes with iron nails or high-heeled hard-soled shoes are not allowed to walk on the membrane surface, and all activities that may damage the finished geomembrane are not allowed.
Chapter VII. Inspection and Repair of Geomembrane Finished Products
1. The operator of the welding machine should mark the welder, name and welding time beside the welded sample and the welded seam to be constructed.
2. During the construction process, the project manager or construction team leader should keep a construction log.
3. The inspection is carried out in three steps, namely visual inspection, inflation inspection and damage test.
4. The visual inspection is mainly to carefully inspect the appearance of the laid geomembrane, the quality of the welding seam, the T-shaped welding, the base debris, etc. All construction personnel should implement this work in the entire construction process.
5. In addition to visual inspection, vacuum inspection should be used for the tightness of all welds, and self-inspection should be strengthened for the parts that cannot be vacuum inspected.
6. The inflation strength of the inflation pressure test is 0.25Mpa, and there is no air leakage for 5 minutes. Considering that the coil is soft and easy to deform, the allowable pressure drop is 20%
7. When the sample blocks taken on the double-track weld are subjected to the tensile test, the standard is that the weld is not torn apart and the mother is torn and damaged during the peeling and shearing tests. At this time, the welding is qualified. If the sample is unqualified, a second piece should be taken from the original weld, and if three pieces are unqualified in a row, the entire weld should be reworked.
8. The samples that have passed the test shall be sent to the owner, general contractor and related units for archives.
9. Defects found in visual inspection, inflatable inspection, and damage test should be repaired in time, and those that cannot be repaired immediately should be marked to prevent omission during repair.
10. In the visual inspection, if it is found that there are defects such as holes on the film surface, and the missing welding, virtual welding, or damage occurred during the welding process, it should be repaired with fresh base metal in time, and each side of the repair scar exceeds the damaged part by 10-20cm. and keep records.
11. For the repaired weld, a detailed visual inspection is generally required to confirm that the repair is reliable before releasing.