Geomembrane

HDPE geomembrane lap process

2020-08-22
High-density polyethylene geomembrane (HDPE geomembrane) laying construction steps.
Chinese name High-density polyethylene geomembrane lap process. Flatness ±2cm/m2, smooth and straight. Compaction degree 95%. Climate requirement 5-40℃ Cleanliness. No tree roots within the vertical depth of 2.50cm.

table of Contents
1 Interface requirements
2 Climate requirements
3 Installation steps
4 matters needing attention
5 Welding preparation
6 Anchor joint requirements
7 Treatment of special parts
8 Welding control

Interface requirements
1 Flatness: ±2cm/m2, smooth and straight;
2 Compaction degree: 95%, geomembrane can be laid on it after rolling;
3 Longitudinal and transverse slopes: the longitudinal and transverse slopes should be above 2%, and the contour boundary and structure at the bottom of the landfill must be conducive to the diversion of leachate;
4 Cleanliness: There should be no sharp-edged debris such as tree roots, rubble, stones, and concrete particles within a vertical depth of 2.50cm.

Climate requirements
1 The temperature is 5-40℃. Taking into account the thermal expansion and contraction of geomembrane, according to experience, when the weather is cold, the geomembrane should be laid tightly; when it is hot, it should be loose; but be careful, avoid noon in summer The high temperature at the time.
2 Wind and rain: The construction should be stopped when the wind exceeds level 4 or when it is rainy; when the wind is small, sandbags should be used to press the geomembrane to facilitate construction.

installation steps
High-density polyethylene geomembrane (HDPE geomembrane) laying construction steps:
1) It should extend from the bottom to the high position, don't stretch it too tightly, and leave a margin of 1.50% for partial sinking and stretching. Considering the actual situation of the project, the slope shall be laid from top to bottom.
2) The longitudinal joints of two adjacent panels should not be on the same horizontal line, and should be staggered by more than 1M.
3) The longitudinal joint should be more than 1.50M away from the dam foot and the bend foot, and should be located on a plane.
4) Slope first, bottom of the field.
5) When laying on a slope, the film spreading direction should be basically parallel to the line of maximum slope.

Precautions
* Slope laying control: Before laying the anti-seepage geomembrane on the side slope, check and measure the laying area first. According to the measured size, transport the anti-seepage membrane matching the size of the warehouse to the first-stage anchoring ditch platform. According to the actual conditions of the site, a convenient way of "push shop" from top to bottom is adopted. The fan-shaped area should be cut reasonably so that the upper and lower ends are firmly anchored.
* Bottom laying control: Before laying the anti-seepage geomembrane, check and measure the laying area, and transport the anti-seepage membrane matching the size in the warehouse to the corresponding position according to the measured size: when laying, manually press a certain amount In the direction of the “push shop”.
* Align and set up: The laying of HDPE geomembrane should be level regardless of the slope or the bottom of the field
Straighten, avoid wrinkles and ripples, so that the two geomembranes are aligned and aligned. Lap width
According to design requirements, it is generally about 10cm.
* Control of pressing film: Use a sandbag to press the aligned and aligned HDPE geomembrane in time to prevent wind blowing.
* Laying control in the anchoring ditch: On the top of the anchoring ditch, a certain anti-seepage film should be reserved according to the design requirements to prepare for local sinking and stretching.
*Longitudinal joints: the upslope section is on the top, the downslope section is on the bottom, and there is enough overlap length ≥15 cm. Figure-1 The slope anti-seepage HDPE geomembrane must be under the membrane. Figure-2 The bottom HDPE geomembrane bentonite After the mat laying acceptance is passed, the area is laid manually according to a certain direction, and the "push paving" is carried out. Figure-3 HDPE geomembrane when laying on the slope --4 Use a sand bag to align and set up the film in a basic direction Parallel to the line of maximum slope. HDPE geomembrane is pressed to prevent wind
  
Welding preparation
Experimental welding requirements
1) The experimental welding is carried out on the HDPE geomembrane sample to inspect and adjust the welding equipment.
2) The welding equipment and welding personnel can only proceed to the next step of productive welding after successfully completing the experimental welding.
3) Frequency control of experimental welding: According to the change of ambient temperature, each machine shall be no less than twice a day, once before the formal operation and once in the middle shift.
4) Experimental welding is performed under the same surface and environmental conditions as production welding.
Welding inspection control measures
Inspection control is divided into product surface inspection and welding seam inspection.
1) Product surface inspection: After the HDPE geomembrane is unfolded, check whether there are any defects with eyes, and mark the defective or suspected places for repair.
2) The inspection of welds is divided into: visual inspection and leak test (non-destructive)
* Visual inspection of welds: It is mainly to carefully check the appearance quality of welds, the treatment of T-type welds and cross-type welds, and whether there are sundries in the base layer.
* The surface of the double welding seam: flat, firm and beautiful, that is, smooth and smooth, with uniform thickness. There should be no other sundries and excess loose solder at the welding seam, and no damaged parts of the surrounding base material should be shown.
* T-type weld surface: tightly combined and smoothly connected.
* Cross-shaped weld surface: Cross-shaped welding can only be used when it is indeed unavoidable, but it must be covered with a patch of more than 20 cm square and completed by an experienced welder.
3) Non-destructive testing: inflatable (double weld).
* Double-welded seam inflation detection: a non-destructive testing method to judge the quality of the welding by checking the air tightness of the double seam. Seal the gas with a certain pressure in the gas cavity, and judge its air tightness by detecting the change of the pressure gauge attached to the needle.
* The composition of the instrument: a compression device, which can produce a pressure of 0.15-0.20Mpa, a hollow needle equipped with a pressure gauge
* Procedure: Inflate the pressure of 0.15-0.20 Mpa, and keep it for more than 2 minutes is qualified; if the pressure gauge is not stable, keep a certain pressure on one side, and apply soap liquid to the outer weld for inspection, if there is no leakage It is considered qualified (that is, the other leaking weld is not treated).
4) Repair of defects: defects found in visual inspection and positive pressure should be repaired in time; those that cannot be repaired immediately should be marked with special marks to prevent missing repairs.
* Various cavities repair: according to the size of the hole, when the hole is larger than 5mm, a 10 cm round or oval pad should be used for repair.
* For small pinholes or voids, spot welding or extrusion welding can be used.
  
Anchor joint requirements
1) Anchor ditch: it fixes the high-density polyethylene geomembrane and protective layer geotextile, and the high-density polyethylene geomembrane and protective layer geotextile are laid.
After that, immediately press down with a concrete board.
2) Buffer platform: For the stability of the high-density polyethylene geomembrane and prevent sliding, a buffer platform is added in the center of the slope, and an anchor trench is set on the platform to reduce the pull-down force of the high-density polyethylene geomembrane and increase stability . Due to the characteristics of the actual terrain, the anchor ditch of the buffer platform of this project is small and narrow, so special attention should be paid during construction.
3) Flood interception ditch: above the anchoring ditch, a flood interception ditch is excavated to divert rainwater from outside to prevent water from directly entering the landfill.
The anchor ditch in the first phase of this project also serves as a flood interception ditch.
  
Special part treatment
1) The intersection of slopes is the corner of the dam slope: Laying and welding are special circumstances, and they must be specially tailored according to the actual conditions to make the geomembrane close to the dam slope base. Otherwise, it will cause "hanging" or "bulging" phenomenon.
Construction points: In this area, the operator must carefully measure and cut the geomembrane into an inverted trapezoid with a wide upper and a narrow bottom.
2) At the intersection of the slope of the reservoir area and the bottom of the reservoir, there are often blind trenches in the design.
Construction key points: First, lay the geomembrane along the dam surface 1.5 meters away from the blind ditch
Then connect with the bottom membrane of the library; the welding of the two adjacent panels is: after welding, press into the blind groove.
3) The connection between the dam pipe and the geomembrane (see the schematic diagram): First cut the HDPE geomembrane into horn-shaped pipe sleeves according to the diameter of the leachate penetrating the dam pipe, and divide them into 6-8 pieces, and then the pipe sleeves from large to large Sleeve the pipe through the dam in a small sequence, then adjust the position of the pipe sleeve appropriately and temporarily fix it with a hot-air torch. The pipe sleeve cannot have any suspended parts. Finally, the large and small sleeves of the pipe sleeve are welded to the HDPE geomembrane and the leachate penetrating dam pipe, and reinforced with stainless steel hoops.
  
Welding control
Control of welding data
1) Whether it is production welding or experimental welding, the welding temperature, speed, and pressure of the clamping rod must be maintained to achieve the best results.
2) Each weld should be inspected.
Welding quality assurance control measures
1) When welding a side slope, the length of the weld should extend along the slope, not across.
2) Minimize the welding of side feet and sporadic film.
3) A welding supervisor should supervise the welding operation.
4) The surface of HDPE geomembrane should be cleaned of grease, moisture, dust, garbage and other debris.
5) If welding is operated at night, there should be sufficient lighting.
6) At the overlap of the HDPE geomembrane, wrinkles should be removed. When the wrinkle size is less than 10 cm, a round or oval patch should be used, and the size of the patch should exceed 5 cm around the incision.
7) When the ambient temperature and unfavorable weather conditions seriously affect the welding of HDPE geomembrane, the operation should be stopped.

8) The welding machine should be maintained regularly, and the residue in the welding machine should be cleaned frequently.




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