How to detect leakage and damage of HDPE geomembrane

1. The principle of HDPE film integrity testing

HDPE geomembrane is widely used in environmental protection, landfill, water conservancy, chemical industry, metallurgy, water supply and drainage, landscape ( Artificial lake), aquaculture, municipal construction and other industries in anti-seepage and anti-corrosion projects.

Geomembrane used in anti-seepage project

As the geomembrane of the anti-seepage project is prone to damage during transportation and construction, the damaged holes will inevitably affect the anti-seepage effect of the project. There are special compliance standards for the material selection standards, construction welding methods and requirements of the anti-seepage geomembrane. The construction of geomembrane anti-seepage materials requires a strict and scientific construction quality assurance system. According to the survey, even if strict construction quality assurance regulations (CQC/CQA) are implemented, the damage and leakage of the geomembrane in the actual project still occurs. Conventional construction quality assurance procedures cannot find damaged holes after the completion of the project. When the geomembrane has overlying materials, even if it is known that the geomembrane is leaking, it cannot be accurately located. The electrical leakage location detection technology can solve this problem well. The basic principle of electrical leakage location detection of geomembrane is simply to apply a voltage on the geomembrane and detect the location of the loop by moving the detection device in the electric potential field to find the leakage point.

The detection results of the leakage position of a large number of geomembrane show that a large number of damages are caused by construction.

1. Geomembrane installation stage 24%

2. Drainage layer/protective soil layer at the construction stage 73%

3. In the later stage of operation 2%

4. The damage of the geomembrane under various conditions during the laying and installation stage:

Several forms of geomembrane installation and construction damage

5. The damage of the drainage layer/protective soil layer of the geomembrane under various conditions during the construction stage:

Comparison of traditional construction quality assurance and electrical leakage and damage detection

Comparison of traditional construction quality assurance and electrical leakage and damage detection traditional construction quality assurance procedures (CQA)-focusing on welds

Electrical leakage and damage detection (ELS)-overall leakage detection after construction is completed

1. During installation and construction, only 5% of the gasket is tested

2. Few weld destructive tests, roughly estimated to be less than 2%

3. A typical weld destructive test is 50 times per 40,000 square meters

4. The 100cm destruction weld test requires 300~350cm extrusion welding

5. The quality assurance procedure stops when the geomembrane installation is completed

1. Electrical leakage and damage detection, an average of 5 holes are found for every 10,000 square meters of area

2. Electrical leakage and damage detection can be carried out after the drainage layer/protective soil layer is laid

3. The most effective way to detect the integrity of geomembrane, non-damaging leakage and damage detection across the entire area

4. Low-cost, high-efficiency anti-seepage geomembrane construction quality assurance effective means

Comparison of long-term leakage monitoring and electrical leakage detection

Long-term leakage monitoring system-monitoring during operation

Electrical leakage and damage detection (ELS)-overall leakage detection after construction is completed

1. An electrode needs to be buried every 3 to 5 meters. The buried electrode may damage the geomembrane, which is not suitable for large-area landfills.

2. During the monitoring of the landfill operation, leakage was found and there was no way to repair it, and the leakage still exists

3. The cables or electrodes are faulty and aging, and cannot be repaired or replaced

4. The cost is very high, the cost per square meter is more than 100 yuan. Invest in the cost of long-term monitoring, you can add two to three layers of geomembrane

1. The detection will be carried out after the construction of the landfill site is completed, and no special pre-embedded electrodes are required.

2. The electrical leakage and damage detection can be carried out after the drainage layer/protective soil layer is laid, and the hole position can be accurately located, and the positioning deviation does not exceed 50cm. After the holes are repaired, the garbage can be landfilled to minimize the occurrence of leakage.

3. The most effective way to detect the integrity of geomembrane

Full-area non-destructive leakage and damage detection

4. Effective means of low-cost and high-efficiency anti-seepage geomembrane construction quality assurance

2. Preliminary preparation for testing

After the inspection engineer arrives at the construction site, follow the on-site inspection order to prevent irrelevant personnel from entering the inspection site, ensure the safety of power supply electrodes inside and outside the site, and ensure sufficient water sources and on-site water spray effects.

Preliminary preparation:

(1) It should be ensured that there is no electric field channel connected to the outside on the side slope. The anti-seepage membrane should not have wet geotextiles, gravel layers, horse tracks, temporary roads, metal water pipes and other materials connected to the surrounding earth, and possible water, dampness and wetness.

(2) Water truck (medium size) or sufficient water source required for testing

(3) Provide supporting power supply (AC with voltage of 220v/50 Hz and authorized power of 3000w) to the inspection site;

(4) 2-3 laborers.

Third, the overall test plan

The following measures and steps have been taken for testing:

1. The reservoir area covers the sand and gravel area

(1) Insulation preparation for the upper and lower layers of the geomembrane on site. Ensure that there is no connected electric field on the side slope.

(2) Buried electrodes. According to the pre-selected area, the equipment is placed, the negative electrode is buried in the middle of the two layers of geomembrane, and the positive electrode is placed on the first layer of geomembrane.

(3) Sprinkle water spray. The leachate guide and drain gravel layer on the geomembrane is in a dry state, and the detection area is sprayed on site to ensure that the detection area is wet to the greatest extent and that it can conduct well.

(4) Test calibration. According to the calibration procedure, this survey uses artificial holes to calibrate the sensitivity of the equipment. Through the calibration, the measurement interval is determined, and the line is set according to the interval determined by the calibration, and the detection cells are divided.

(5) Actual measurement. Spray on-site to ensure that the gravel covering on the geomembrane is in a wet state, and measure one data at intervals of about one meter. In order to ensure the accuracy of detection, the measurement interval is 1m×0.5m in the actual survey process.

(6) Analysis of leakage points. Determine the location of the leakage point according to the changes in the voltage data.

(7) Excavation of possible leakage hole area, the excavation area is 50cm area around the determined suspicious point. Cut the geotextile and check the damage. If the first layer of geomembrane is damaged, the composite drainage net needs to be cut to check whether the second layer of geomembrane is damaged. Determine the hole, take a picture and record the position of the hole. If no holes are found after excavation, continue to reduce the detection interval and carefully measure to determine whether it is a misjudgment.

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Four, detection method

Geomembrane electrical leakage location detection is currently the most reliable and effective on-site technical method for detecting the leakage location of anti-seepage geomembrane. The basic principle is simply to apply a voltage on the geomembrane and detect a loop by moving the detection device in the electric potential field. To find the leakage point.

Up to 97% of the geomembrane defects are caused during the construction process, and it is difficult and impossible to control the construction damage of the geomembrane with the traditional construction quality assurance system. The operator's carelessness or failure to follow scientific procedures will cause a lot of damage to the geomembrane. After the construction of the drainage layer/protective soil layer on the geomembrane is completed, the use of electrical leakage location detection is the most effective means to ensure the quality of the anti-seepage project.

For this inspection service, our company uses the dual-electrode method to detect the integrity of the geomembrane at the bottom of the reservoir area. For the detection of the bare leaking membrane, our company uses the water gun method and electric spark to detect the location of the geomembrane leakage.

Schematic diagram of detection of leakage location of geomembrane by two-electrode method

Special industrial and mining conditions need to be paid to the detection of leakage location of geomembrane by the double-electrode method. If there is electrical contact with the soil outside the location detection area, necessary insulation treatment is required; the geomembrane covered by the gravel layer needs to be wetted with the gravel to ensure its conductivity.

During the test, a power supply electrode is placed in the upper and lower media of the anti-seepage HDPE membrane, the negative electrode is placed under the geomembrane, the positive electrode is placed on the main anti-seepage geomembrane, and both ends of the power supply electrode are connected to both ends of the excitation power supply. Under normal circumstances, when the HDPE film is intact, no current flows in the power supply circuit; when there are holes in the HDPE film, current will be generated in the circuit, and a stable current field will be formed in the medium above and below the film. The distribution law of the electric potential is used to locate the loopholes.

Schematic diagram of detection of leakage position of geomembrane by water gun method

Water gun method geomembrane leakage location detection can be used to detect leakage of geomembrane without covering (protective soil, geotextile, etc.). This technique is particularly suitable for use during geomembrane installation or after cleaning. Water gun method geomembrane leakage location detection is an important tool for the quality assurance of geomembrane installation projects.

The detection of the leakage position of the water gun method needs to adopt different detection measures according to various actual industries and mines to ensure good contact between the geomembrane and the foundation layer.

The principle of detecting leakage position of geomembrane by electric spark method

The spark detection method is used in exposed application areas and can be performed during or after installation. It can detect even very small holes, and spark detection is faster and more thorough than any other method.

Precautions:

1. For the detected holes, the anti-seepage construction contractor needs to excavate and repair in time to re-examine the leaking hole area.

2. The electrical leakage location detection method can detect the loop caused by the leakage of a small hole in the geomembrane, so as to find the leakage point. On-site testing conditions include sprinkling and drenching conditions, insulation conditions, as well as the heterogeneity of the site environment and other unforeseeable and difficult-to-control conditions, and other non-geomembrane leakage causes will also cause the loop to be generated, and the resulting non-seepage False alarms or missed detections of missing points are within the normal range.

There are two methods for construction welding of HDPE geomembrane: double seam hot melt welding and single seam extrusion welding. Among them, single seam extrusion welding is mainly used for welding some parts that cannot be welded by double seam hot-melt welding machines and repairing welding defects and damaged parts.

1. Construction requirements for single seam extrusion welding:

a. Check whether the overlap width at the weld seam is appropriate. The film at the seam should be flat and moderately tight so as not to form a "fish mouth"; b. Positioning bonding: use a hot air gun to bond the overlapped parts of the two films , The spacing between bonding points should not be greater than 60-80mm. To control the temperature of the hot air, the HDPE geomembrane must not be scalded, nor can it be easily torn; c. Fuzzing: Use a fuzzing machine to fuzz the film surface within the width of 30-40mm at the weld to achieve thorough cleaning and form Rough surface; in order to increase its contact area, but its depth should not exceed 10% of the film thickness, and the rough surface should be operated gently to minimize damage to the film surface. For the film with thickness equal to or greater than 2mm, a 45° bevel should be made; d. When welding, the machine head should be aligned with the seam, and no offset, slip welding and skip welding are not allowed; e. The thickness of the weld center is general It should be 2.5 times the thickness of the impermeable membrane, and not less than 3mm; f. When a joint cannot be welded continuously, the welded seam of the stubble part should be roughened at least 50mm, and then lap welding; g. The welding rod used, Before entering the machine, it must be kept clean and dry, and the welding rod must not be wiped with oily, dirty gloves, dirty cloth, cotton yarn, etc.; h. According to the temperature, the welding seam should be immediately cooled;

i. When the extrusion welding operation is interrupted for some reason, the extrusion amount of the electrode must be slowly reduced, and the welding should not be suddenly interrupted. When re-construction, the welding should be performed after the interruption.

2. Defect detection and repair

​1. Defect inspection should be done in all places where there are welds and no welds.

​2. Defect marking 3 steps: a. Any damage to the weld or other parts should be circled, and marked with P in the circle to indicate that it needs to be repaired; b. If the damage is not as serious as an actual hole, only need Circled, it means that it can be repaired by extrusion welding; c. After all damage is repaired, a non-destructive test is required. Finally, the person in charge of the site should do a final comprehensive inspection.

​3, patch

​A. The following methods are used alone or in combination: 1) holes, tears, and uneven distribution of HDPE geomembrane raw materials — use extrusion welding to repair; 2) small-scale repairs caused by extrusion welding — re-welding after grinding; 3) no Welding seam that passed—covered with a layer of HDPE geomembrane and re-welded. b. When repairing, pay attention to the clean and dry site to ensure that the equipment is normal and there is no malfunction.

C. All repairs or coverings must extend beyond the damaged part by at least 120cm, and must be rounded corners.

d. If the construction environment permits, you can choose the special glue for geomembrane KS for bonding repair. The bonding repair technology is simple and efficient.

Precautions for geomembrane joints

(1) The joint treatment of the geomembrane is a key construction procedure, which directly affects the operating life of the project. According to quality inspections, the thermal welding method is ideal. (Special glue can also be used for bonding) The hot welding method is to heat the surface of the PE geomembrane to melt the surface, and then use pressure to fuse them into a whole. (2) The geomembrane is best to be laid in a certain direction, the geomembrane A certain pe membrane and pet non-adhesive layer are reserved on both sides, and the direction of each unit geomembrane should be adjusted when laying, so as to facilitate the welding of the two units of geomembrane. (3) After the geomembrane is laid, it should be pressed with a sand bag to prevent wind, and there must be no dirt, moisture, dust, etc. at the edge joints. (4) Before welding, adjust the two sides of the pe single film at the seam so that it overlaps a certain wide band, and is flat and without wrinkles. (5) When welding, it is best to weld by a technician with certain experience, and use a special welding machine for welding. To adjust the temperature and speed, (adhesive can also be used). According to many years of practice, the thickness of the geomembrane is not less than 0.25mm. If it is too thin, it may produce pores, and it is easy to be damaged during construction and reduce the anti-seepage effect. In the construction of geomembrane, special attention should be paid to ensure that the laying should not be too tight, not wrinkled, and the splicing must be firm. Construction should be carried out in strict accordance with the technical specifications, and the five quality barriers of preparation, laying, splicing, inspection and backfilling should be checked.

Shandong Jianbiao Technical Testing and Testing Co., Ltd. (JBJC for short) is a testing and testing organization with CMA testing qualification approved by the State Bureau of Quality and Technical Supervision and established in accordance with the law. In order to ensure the ecological safety of environmental protection projects, Shandong Jianbiao Technology Test and Inspection Co., Ltd. was established in August 2016. The company is engaged in the detection of environmental protection related materials such as building waterproof materials, geosynthetics, and leakage detection of anti-seepage engineering anti-seepage systems. With the large-scale application of anti-seepage materials and building waterproof materials in related projects, the safety of project leakage directly affects the safety and quality of the project. Leakage detection can objectively, fairly, scientifically and effectively supervise the project quality to truly ensure anti-seepage The quality and safety of the project.