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Geomembrane quality control of cofferdam in Wudongde Hydropower Station

Abstract: Deep foundation pit and high reclamation in construction are one of the key technical problems of Wudongde Hydropower Project. The composite HDPE geomembrane for sale is an important part of the anti-seepage system of the cofferdam. In order to ensure the construction conditions of the dam foundation dry pit, the quality control of the wholesale HDPE Liner made in China process is especially important. The Wudongde Hydropower Project passed the quality control of the HDPE geomembrane manufacturers process of the cofferdam. After the completion of the cofferdam project, it passed the inspection of one flood season and achieved good results.

Keywords: high quality HDPE geomembrane; anti-seepage; quality control; cofferdam; Wudongde Hydropower Station


The river bed cofferdam of Wudongde Hydropower Station is designed as three-level water retaining structure, and the water-retaining standard is designed according to the 50-year flood. The upper and lower cofferdams adopt the structure of earth-rock cofferdam, and the anti-seepage of the carcass adopts the form of “composite HDPE geomembrane for sale + plastic concrete anti-seepage wall + curtain grouting under the wall”. The upstream dome elevation is 873.00m, the dome width is 10m, and the maximum height is 67m. The elevation 832.00~841.00m section is vertical anti-seepage. The elevation 841.00~873.00m section is slope anti-seepage, anti-seepage head 41m, anti-seepage level II. The maximum height of the composite China HDPE liner manufacturers inclined wall is 40.0m; the maximum depth of the plastic concrete cutoff wall is 90.5m and the thickness is 1.2m; the bottom line elevation of the curtain is 727.00m, and the maximum hole depth is 130.0m. The downstream dome elevation is 847.00m, the dome width is 10m, and the maximum raft height is 42m. The elevation 829.00~847.00m section adopts vertical wall anti-seepage, anti-seepage head 18m, anti-seepage level 3; China HDPE liner factory price core wall maximum height 17.5 m; the maximum depth of the plastic concrete cut-off wall is 91.0m, the thickness is 1.2m; the bottom line elevation of the curtain is 728.00m, and the maximum hole depth is 101.0m. The composite HDPE geomembrane manufacturers of the cofferdam adopt “two cloths and one film”, and the film material is high density polyethylene wholesale HDPE Liner made in China (HDPE). The structure of the low price China HDPE liner anti-seepage body from top to bottom is: protective layer reinforced stone cage, shotcrete concrete, anti-seepage layer composite high quality HDPE geomembrane, support layer without sand concrete.

The quality of composite HDPE geomembrane for sale construction in the cofferdam anti-seepage structure of Wudongde Hydropower Station directly affects the anti-seepage effect of the cofferdam, and the quality control of the China HDPE liner manufacturers construction process must be done before, during and after the three stages.

ASTM Standard HDPE Geomembrane Liner HDPE For Landfill Dam Lagoon Oil Tank Fish Pond Liner

1. Pre-existing quality control

1.1 Raw materials beforehand control
1.1.1 Geomembrane design performance indicators
(1) Tensile strength (warp and weft) ≥ 20kN/m;
(2) The main film thickness of the upstream cofferdam is ≥1.2mm, and the geotextile is 500g/m3;
(3) permeability coefficient K = i × 10-11 ~ i × 10-12cm / s;
(4) Elongation ε>30% (designed as elongation at break);
(5) Hydrostatic pressure resistance > 0.5 MPa.

1.1.2 Geomembrane approach acceptance, sampling inspection, and visual inspection
(1) Entry acceptance
After the HDPE geomembrane manufacturers are on the scene, the acceptance items include the delivery list, the test report, the certificate of conformity and other quality certificates for the ex-factory products.
(2) Approach sampling test
The number of sampling inspections shall be the inspection lot according to the same variety and the same specification of the delivery batch number. For the batch of ≤50 rolls in the same batch of products, at least 2 rolls shall be sampled; >50 rolls shall be sampled at least 3 rolls. The characteristic test items are thickness, breaking strength, elongation at break, tear strength, and permeability coefficient. The specific test results are shown in Table 1.
(3) Appearance quality inspection
Before the China HDPE liner factory price is laid, each roll of HDPE geomembrane for sale must be inspected for appearance quality. Appearance quality is divided into two types: light defects and heavy defects. Heavy defects are not allowed. Light defects should not exceed 5 per 200m2. China HDPE liner manufacturers whose appearance quality does not meet the requirements are prohibited.

1.2 Pre-control of construction technology
(1) The supervision unit organizes a technical meeting to enable the construction unit to fully understand the characteristics of the process technology.
(2) The construction unit combines the technical characteristics of the process, prepares special technical plans and operation instructions, and forms a guarantee system from the aspects of organization, system, measures, and economy.
(3) According to the engineering structure and design requirements, the construction unit draws the HDPE geomembrane manufacturers laying sequence and the partitioning block diagram, and numbers each weld of the low price China HDPE liner.
(4) The construction unit shall conduct pre-job training for the welding, quality inspection, and test and inspection personnel of the China HDPE liner factory price construction. Only after passing the examination can the employee be employed, and the personnel replacement must be approved by the supervisor.
(5) The construction unit shall report the performance, technical parameters and quantity of the selected welding and testing equipment to the supervisor for the record. After the equipment enters the scene, the supervisor shall check according to the equipment list, and the equipment replacement must be submitted to the supervisor for approval.
(6) The perimeter of the high quality HDPE geomembrane working area should be protected by safety and enclosure, and closed management should be implemented.

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2. Quality control in the matter

2.1 Geomembrane storage and transportation
(1) The construction unit shall set up an HDPE geomembrane for sale stacking warehouse that meets the requirements, and arrange special personnel management, and at the same time do a good job in the management of the China HDPE liner factory price. The application form must be completed after the application and withdrawal of the library and can be carried out after confirmation by the on-site supervision.
(2) If the China HDPE liner manufacturers transportation loading and unloading process are carried out by manual hoisting and unloading, the sling rope should be made of flexible woven tape such as nylon woven tape, and ropes such as steel wire ropes should not be used for direct hoisting.

2.2 Geomembrane welding process test
(1) The welding process test at the construction site includes hot-melt welding and extrusion welding, and the process test does not replace the test welding.
(2) Determine the welding parameters such as welding temperature, preheating temperature and welding speed of the HDPE geomembrane manufacturers welding construction through the welding process test.
(3) After completing the process test, organize the participating parties to conduct the process test review and confirm the test results.

2.3 Geomembrane construction
2.3.1 Site construction requirements
(1) After the commencement of the laying of low price China HDPE liner, it is strictly forbidden to carry out excavation, shooting, drilling, electric welding, burning, drainage, transportation, and other cross operations within the scope that may endanger the safety of high quality HDPE geomembrane. The low price China HDPE liner construction site is strictly prohibited from smoking or using various kinds of materials. Fire source.
(2) All personnel entering the China HDPE liner factory price construction site must wear soft-soled shoes or cotton socks, and must not wear spikes, high-heeled shoes and hard-soled shoes.
(3) All vehicles and construction machinery are prohibited from entering the scope of welding and laying. Except for the inspection personnel, other idle personnel is not allowed to enter.
(4) During the construction process of HDPE geomembrane manufacturers, the construction unit shall conscientiously implement the three-level inspection system. Each process shall be carried out in the next process after the construction unit has passed the three-inspection self-inspection and the supervision unit has passed the re-inspection.

2.3.2 Geomembrane construction procedures and precautions
Geomembrane construction procedure: support layer clearing cone sharpening → stakeout → laying wholesale HDPE Liner made in China →  cutting → test welding low price China HDPE liner → weldment inspection → welding wholesale HDPE Liner made in China → sampling inspection → temporary compaction → inspection acceptance.
(1) Remove all kinds of cones and sharp edges on the support layer within the scope of HDPE geomembrane for sale laying.
(2) Before laying the wholesale HDPE Liner made in China, the construction unit shall carry out on-site measurement stakeout and marking, and accurately locate the position of each membrane block.
(3) The wholesale HDPE Liner made in China roll unfolded every day shall not exceed the welding range of the day; and in the event of inclement weather, the number of rolls of China HDPE liner factory price unfolded shall be appropriately reduced.
(4) The cutting of the China HDPE liner manufacturers shall be carried out in a hard and slab site which is flat and wide and cannot have a damaged film. Before cutting, the relevant laying dimensions shall be measured, then cut according to the actual size, and recorded by piece number. The number shall be unique and not repeated. wholesale HDPE Liner made in China cutting must use a special hook knife.
(5) When laying large or whole wholesale HDPE Liner made in China on the slope, the method of free sliding by gravity cannot be used. The China HDPE liner factory price coil should be controlled when it is opened, such as pulling, lifting or rolling up. The laying method must ensure that the HDPE geomembrane manufacturers and any other underlying geotechnical materials are not damaged.
(6) Each piece of low price China HDPE liner that has been installed must be clearly marked with ink that is not easily rubbed: the laying order number, the volume number, and the date of laying.
(7) When the high quality HDPE geomembrane is laid, the dimensional change caused by thermal expansion and contraction of the material should be considered, and the amount of expansion and contraction should be reserved, and the high-temperature period at noon in summer should be avoided.
(8) Adequate temporary ballast should be prepared at the construction site. All exposed HDPE geomembrane for sale edges must be pressed with ballast or old tires to prevent the high quality HDPE geomembrane from being blown by the wind and pulled out of the surrounding anchorage ditch.

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2.3.3 Welding and sampling requirements
(1) Geomembrane welding includes two types of hot-melt welding and extrusion welding. Hot-melt welding is the main welding method in construction. The extrusion welding method is mainly used for repairing and welding where the hot-melt welding machine cannot reach. After the laying and unfolding are completed, it must be welded in time, and the lap length is controlled according to hot-melt welding (100±25) mm and extrusion welding (75±20) mm.
(2) Three samples were taken for each welding test, one for each end of the weld and one for the middle. The sample width is 25.4mm and the length should meet the testing requirements of the tensile machine. Two samples at the end were subjected to the peeling test, and the intermediate sample was tested for bonding seam welding force (shearing force), and the test results should meet the requirements.

2.4 Repair requirements
(1) All defects that occur during the construction process must be clearly marked on the HDPE geomembrane manufacturers and the defect information recorded.
(2) After the repair is qualified, the construction unit shall record on the surface of the China HDPE liner factory price: the date and time of repair, and the signature of the technician. And record the low price China HDPE liner repair information.
(3) The main form of China HDPE liner manufacturers defect repair

2.4.1 patch repair
The patch is suitable for repairing all tears, holes and pinhole holes through the entire HDPE geomembrane for sale (except for pinholes for vacuum detection), and can also be used to cover uneven resin and foreign matter (such as gasoline, oil, etc.). Parts, or other surface defects. The patch is generally round, the size must exceed the defect range of 200mm, and the patch is guaranteed to be flat and not curled.

Patches and defects must be free of dirt, moisture, impurities, and signs. Before repairing the weld, the patch shall be temporarily bonded to the surface of the China HDPE liner factory price by means of a hot air torch; the rough surface shall be ground with an angle grinder around the patch and a beveled edge shall be produced at the seam. Grinding must be completed within 1 h of permanent welding. Hot air welding torches and grinding shall not cause excessive melting, wear or hole penetration of the high quality HDPE geomembrane.

Minimize the number of patches. Adjacent defects must be repaired with a large patch. Where there are too many patches, a patch or HDPE geomembrane manufacturers repair should be used.

2.4.2 Squeeze the seam cap (cap)
The extruded joint cap is suitable for repairing unqualified lap welds. The surface of the joint must be ground with an angle grinder before repairing, and the joints are also ground to produce a rough surface at the place where the weld is welded. And create a beveled edge at the seam. Grinding must be completed within 1 h of repair welding. Grinding does not cause excessive wear or penetration of the film and does not significantly exceed the range of extrusion welding.

2.4.3 Grinding and welding
Abrasive extrusion welding is suitable for repairing small extrusion joint defects of less than 300 mm in length, as well as small surface damage and local defects that do not penetrate the entire China HDPE liner manufacturers thickness.
Before welding, it must be ground in the repaired area to produce a rough surface. The grinding must be completed within 1 hour before permanent welding.

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2.5 Geomembrane construction interference problem
(1) During the construction of low price China HDPE liner, there will be cross-over work with cofferdam filling, protective layer spray concrete, stone cage hoisting, and peripheral curtain grouting. Generally, follow the principle of “upper-level construction and lower-level shutdown” to avoid the phenomenon of cross-over work as much as possible.
(2) It is impossible to avoid the intersection of the wholesale HDPE Liner made in China and other parts of the work, or the other parts of the China HDPE liner manufacturers that has been completed for construction, the construction unit should take the sand film on the surface of the high quality HDPE geomembrane (with a range of not less than 10m) to take protective measures. Other construction units must also formulate comprehensive and effective protective measures, and they can be carried out after passing the inspection and acceptance by the supervision unit.

2.6 Rainy season construction measures
(1) In order to effectively control the welding quality of the anti-seepage film, the two anti-seepage film joints to be welded must be wiped clean and dry with a clean gauze during the rainy season. If necessary, the air can be slightly dried by a hot air blower to ensure weld welding. quality.
(2) During the rainy season construction, the maintenance work on the welder should be strengthened. After the daily welding construction, the welding machine should be wiped clean with a clean cotton cloth; when it is raining, the waterproofing plastic cloth should be used to wrap the welding machine and put it in a dry place to reduce the humidity of the welding machine circuit board and sensors. Damage caused.
(3) During the construction after rain, the welding parameters must be adjusted, and the test welding can pass the test before construction.
(4) Keep abreast of the weather forecast for the next 3 to 5 days, and arrange the construction progress according to the weather changes.
(5) The paved film must be welded in time to avoid the construction of the bottom of the field due to the leakage of rain and water.

3. After-the-fact quality control

3.1 Geomembrane welding quality inspection
(1) Non-destructive testing
The construction unit shall perform non-destructive testing on each weld, and the test shall be carried out 4 hours after the completion of the welding. The hot-melt welding shall be carried out with air pressure test, and the pass rate shall be 100%; the extrusion welding shall be carried out according to the weld condition to carry out vacuum test or electric spark test method, and the pass rate is 100%.
(2) Destructive test sample quantity
The construction unit shall take samples of the weld HDPE geomembrane for sale on the laid low price China HDPE liner for destructive testing of the weld. At the initial stage of the construction, a 1000mm×350mm sample shall be taken at approximately 1000m2, and gradually decrease to 5000m2~10000m2 as the welder level increases and the welding area increases. One sample was taken and the strength test required a pass rate of 100%.
(3) Weld strength destructive testing requirements and results
Ten standard pieces of 25.4 mm width were cut for each sample, and five shear tests and five peel tests were performed. At least 4 of the test results of 5 samples of each experiment shall meet the requirements, and the average value shall meet the standard value requirement, and the minimum value shall not be less than 80% of the standard value.

If the strength test cannot be passed, the test shall be resampled within 6 m of each end of the weld at the position where the test failed, and the above process is repeated until it is qualified. Reinforce the parts that are suspected of being squashed by extrusion welding.

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4. Conclusion

By strengthening the quality control of the high quality HDPE geomembrane construction process, the Wudongde Hydropower Station cofferdam project effectively protected the cofferdam anti-seepage effect during construction. After the completion of the cofferdam project, it passed a period of inspection and it worked well. Although the China HDPE liner manufacturers construction is simple, the process requirements are high, especially the hot welding process is difficult to grasp, the detection method is difficult to grasp, and it is necessary to train skilled welding operators to specifically solve various welding quality problems appearing on the spot.

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