This “Geomembrane Construction Method Rules” is developed for special impermeable projects in HDPE geomembrane construction method, the primary contains HDPE geomembrane laying and geomembrane welding two aspects, detailed introduction in the impermeable project laying method and welding should pay attention to matters, is the necessary material for construction units.
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1 Laying of HDPE geomembranes
- HDPE geomembrane should be laid by the corresponding qualified acceptance documents of civil engineering before laying.
- Before cutting HDPE membranes, their relevant scales should be accurately measured and then cut according to practice. It is generally not advisable to cut them according to the scales shown in the drawings, and they should be numbered piece by piece and recorded in detail on a special form.
- HDPE geomembranes should be laid with fewer welds to save as much raw material as possible under the premise of quality assurance. It is also simple to ensure quality.
- The lap width of the joints between geomembranes is generally not less than 10cm, generally so that the weld is placed parallel to the direction of the major slope, i.e. along the direction of the slope.
- Generally in corners and deformed sections, it should be that the length of the joint is reduced as much as possible. Except for special requirements, no weld seam should be provided within 1.5m from the top slope or stress concentration area on slopes with a slope greater than 1:6.
- HDPE geomembranes should be laid in such a way as to prevent artificial wrinkles and should be stretched as tightly as possible and laid flat when the temperature is low.
- After the HDPE geomembrane has been laid, walking on the membrane surface and moving tools should be minimised. Any objects that can pose a hazard to the HDPE membrane should not be placed on the membrane or carried on the membrane to prevent accidental hazards to the membrane.
2 HDPE Geomembrane Construction Method
Foundation Acceptance
The compaction of the foundation bedding layer of the pit bottom and slope should reach 95% of the design requirements to ensure that the surface is smooth, without obvious unevenness, and without water, mud, masonry tiles, branches, roots, weeds, sharp particles, hard debris and any substances that may damage the impermeable material, the geomembrane. The bottom surface of the pit should be ensured to have a 2% slope of the pit bottom from west to east, and a 2% slope to form a sloping bottom in the direction of the inflow canal with the inflow trunk canal as the axis respectively in the north-south direction. During the whole process of laying the impermeable layer, it should be ensured that the surface of the pit bedding layer is not affected by moisture, and any possible routine changes in the surface of the foundation bedding layer should be checked and remedied at any time, and the design requirements must still be met after remediation.
No smoking, no shoes with heels and nails, no work on paved geomembranes, all measuring tools, etc. must be handled lightly, no stabbing of the geomembrane, no squeezing of the welding machine heat part shall touch the geomembrane.
3 Welding construction of geomembranes
Welding construction must be synchronized with the laying of the membrane, laying a welding piece.
The slope geomembrane is laid from top to bottom, a bottom is not spliced, the upper end leaves the slope shoulder and anchor amount, the lower end to the bottom of the pit leaves the head from the slope root not less than 1.8 m, the upper and lower film ends are aligned, using the hot wedge welding machine, the slope shoulder empty welding part with squeeze welding machine welding.
The corner seam should be avoided as far as possible, and the irregular shape should be reduced to a minimum.
Cross welds must be patched with a squeeze welder and the length of the patches must not be less than 20 cm. The weld must be trimmed to reveal the weld stubble before it is patched, and then the patch must be welded with a hand-held abrasive wheel.
When the geomembrane of the slope is welded to 20 panels, 5-15 panels can be buried in the anchorage ditch for anchoring, after which one panel is welded and one panel is anchored, and 5 panels on each side are always kept unanchored, and only sand (soil) bags are used for wind protection.
Geomembrane laying and welding at the bottom of the pit
The direction of laying film is from north to south, one from the beginning to the end, several volumes of geomembrane need to be spliced together, at this time several volumes of geomembrane of similar width must be selected for splicing, after splicing, one side of it and the western slope of the geomembrane head welded to the bottom of the pit with a wedge welding machine, and use the squeeze welding machine to make up for all cross welds, but the geomembrane north and south are not anchored.
4 Welding of HDPE geomembranes
- The welding process of the hot wedge welder is divided into: adjusting the pressure setting the temperature setting the speed welding seam lap check loading the film into the machine starting the motor pressurising the welding.
- The joint should not have oil, dust, HDPE geomembrane lap section surface should not have mud and sand and other debris, when there is debris in the welding before the necessary clean up.
- When welding starts every day, it is necessary to test weld a 0.9mm x 0.3mm specimen at the scene first, with a lap width of not less than 10cm, and use a tensile machine to carry out peel and shear tests at the scene, after the specimen is qualified, it can be used to adjust the speed, pressure and temperature at the time to carry out exactly the welding. The specimen should be marked with the date, time and ambient temperature. Hot wedge welding machine in the welding process, need to keep an eye on the operation of the welding machine, according to the actual situation on site speed and temperature fine-tuning.
- The welding seam must be neat and beautiful, and there must be no slip welding or jumping away.
- When the length of the geomembrane is not available, the longitudinal seam should be welded first, and then the longitudinal seam should be welded, and the transverse seams should be T-shaped at a distance of more than 50cm, without crosses.
- Adjacent geomembrane welds should be staggered lap as far as possible, the junction between the membrane blocks should be T-shaped, minimize cross-shaped, longitudinal mode to the intersection of the weld using the kneading welder to strengthen.
- When welding the membrane, no dead folding is allowed. When laying HDPE geomembranes, the amount of elastic deformation caused by temperature change is reserved according to the local temperature change and the functional requirements of HDPE geomembranes.
- When the temperature of the welding machine indicated by the temperature control of the portable welding machine is lower than 200℃, it should be dusted off with clean cloth or cotton yarn before welding, and if necessary, it should be re-polished, and should not be rubbed by hand.
- When the seam is affected by dew, wetness, mud and sand, treat it before welding.
- During rain or joints with moisture, dew, or perhaps large sand can not be welded, but the adoption of protective methods is outside.
- When the temperature is below 5°C, no work should be carried out in accordance with the standard requirements, and if work is necessary, the welding machine should be preheated before welding.
- Knead welding machine in the welding process, should often check the slider of the gun head, wear more serious should be timely replacement of the slider, to prevent harm membrane surface.
- Geomembranes should be powered by a generator with good voltage regulation when welding, and in special cases when local electricity is used, it is necessary to use a voltage regulator.
5 HDPE Geomembrane Seam Reminders
(1) Geomembrane seam processing is the key procedure of construction, directly affecting the life of the project, according to quality testing shows that the use of heat welding method is more favorable. (also available with special glue joint) heat welding method is PE geomembrane connected appearance heating treatment so that the appearance of melting, and then through the pressure to make it melt into one.
(2) geomembrane good along a certain direction, geomembrane both ends are reserved for a certain PE film and PET does not bond layer, laying to adjust each unit of geomembrane towards, in order to facilitate the welding of two units of geomembrane.
(3) After the geomembrane is laid, it should be pressed with sandbags to prevent wind movement, and the edge joints should not be required to have dirt, moisture, dust, etc.
(4) Before welding, adjust the two edges of the PE single film at the seam so that it laps a certain wideband and is flat and wrinkle-free.
(5) When welding, it is good to have a certain experience of technical welding, welding using a special welding machine for welding. To adjust the temperature and speed, (can also glue joint).
According to years of practice, the thickness of geomembrane is not less than 0.25 mm, too thin may produce porosity, and easy to be damaged in construction and reduce the role of seepage control. Geomembrane construction, especially to pay attention to do laying should not be too tight, shall not be wrinkled, splicing to the firm. To strictly follow the technical standards of construction, prepare, lay, splice, check and backfill, etc. five quality barriers.
(1) geomembrane seam processing is the key procedure of construction, directly affecting the life of the project, according to quality testing shows that the use of heat welding method is more ideal. (also available with a special adhesive) heat welding method is PE geomembrane connected surface heating treatment, so that the surface melted, and then through the pressure to make it fusion into one.
(2) Geomembranes are best laid in a certain direction, with both sides of the geomembrane reserved for a certain PE film and PET non-adhesive layer, and each unit of geomembrane should be adjusted to facilitate the welding of two units of geomembranes when laid.
(3) After the geomembrane is laid, it should be pressed with sandbags to prevent wind movement, and the edge joints are required not to have dirt, moisture, dust, etc.
(4) Before welding, adjust the two edges of the PE single film at the seam so that it laps a certain wideband and is flat and wrinkle-free.
(5) When welding, it is best to weld with technicians who have some experience, and weld using special welding machines for welding. To adjust the temperature and speed, (can also be glued together).
According to years of practice, the thickness of geomembranes is not less than 0.25 mm, too thin may produce porosity, and easy to damage in construction and reduce the effect of seepage control. In the construction of geomembranes, special attention should be paid to the fact that they should not be laid too tightly, should not be wrinkled, and should be firmly spliced. We should strictly follow the technical specifications for construction, and make sure that the five quality gates are prepared, laid, spliced, inspected, and backfilled.
1. It should be extended from the bottom to the high level, not stretched too tightly, and a margin of 1.50% should be left for local sinking and stretching. Taking into account the actual situation of the project, the slope of the edge takes the order of laying from top to bottom
2. the longitudinal joints of two adjacent widths should not be on a horizontal line and should be staggered by more than 1m from each other
3. the longitudinal joints should be more than 1.50 m away from the foot of the dam, at the foot of the bend, and should be located on the plane
4. side slopes first and then the bottom of the field.
5、When laying on the side slope, the direction of film spreading should be basically parallel to the maximum slope line
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