Installation requirements and specifications for high-density polyethylene (HDPE) geomembranes

Before installing HDPE geomembranes, the substrate surface must be inspected to ensure that it meets the design requirements and construction conditions. The base must be dry, compacted, level, without cracks, protruding irregularities, dirt or depressions. At a depth of up to 25 mm there should be no tree roots, stones, debris, ends of fittings or glass fragments. Its plane should have gradual deviations within acceptable limits, with uniform and constant slopes in accordance with the design drawings, providing an optimal working surface for laying the HDPE geomembrane.

The capping soil over the HDPE geomembrane should also be free of sharp objects such as sharp rocks or sharp branches. Stones in the soil should be round, with a diameter of no more than 20 mm. When laying cover soil over HDPE geomembrane, avoid creating artificial folds when using a bulldozer. For small bulldozers, place a bed of at least 300mm thick cover soil between the bulldozer and the HDPE geomembrane; for large bulldozers, lay a bed of cover soil at least 450 mm thick.

When laying soil over an HDPE geomembrane after installation, walking or moving tools on the surface of the membrane should be kept to a minimum. Any objects that could damage the HDPE geomembrane should not be placed on it or carried while walking on it to prevent accidental damage.

1. Preparing for installation

Before installation, the installation base must be inspected with the relevant departments. Installation can only proceed if the following conditions are met: The base must be solid and level. Within the vertical depth of 25 mm there should be no debris such as tree roots, crushed stones, stones, concrete particles, ends of reinforcement or glass fragments that could damage the geomembrane. When laying on backfill soil, the degree of compaction of the backfill must be at least 95%. The previous process (civil engineering or geomembrane installation) must be completed and accepted.

The base must be free of seepage, silt, standing water, organic residues or environmentally hazardous substances. The corners of the base must be rounded with a minimum radius of 500 mm. The outside temperature should exceed 5°C, the wind speed should not exceed 4 on the Beaufort scale, and there should be no rain or snow. Based on on-site measurements, low-density polyethylene membranes were cut, numbered and fully documented.

2. Installation process

Installation of the polyethylene composite membrane should be carried out in accordance with the process described in the diagram above.

3. Laying the geomembrane

First, transfer the pre-cut and numbered geomembrane sections to the designated locations on site. Make sure that the installation area matches the numbering of each membrane. Once confirmed, place the membranes and immediately secure them temporarily with sandbags. Check the width of the slab to ensure it is at least 10 cm. During installation in critical areas such as reservoir base slopes, bends and slope junctions, ensure that the sub-base transitions smoothly at bends without negative slopes. Lay the membrane as loosely as possible to prevent hanging due to tension.

Avoid hand creasing during installation. Consider thermal expansion and contraction based on local temperature variations, site topography, and membrane properties. During installation, constantly check the surface of the membrane for defects such as water spots, pits, holes or folds. Replace any nonconforming material immediately. In corners and uneven areas, minimize the length of joints. Unless otherwise specified, joints with a horizontal angle of less than 45 degrees should not be located within 1.5 meters of crests or stress concentration areas on slopes greater than 1:6.

4. Quarrel

Preparation before welding

Before welding, make sure the surfaces to be welded are clean. They should be free of dirt, sand, accumulation of water (including dew) or debris. Make sure the overlap width is correct (minimum 10 cm).

Trial quarrel

Initial welding should begin with test welds on site. Adjust the weld to verify proper fit. Formal welding may proceed only after all parameters meet specifications.

5. Welding process

Geomembrane seams must be welded using a dual-lane hot welding machine. The welding process is as follows:

6. Technical requirements and precautions for welding

Adjust the operating temperature and speed of the welding machine depending on the ambient temperature and the properties of the geomembrane. The geomembrane at the welded seam must be fused into a single solid fabric. Incomplete, missed or redundant welds are not permitted. Overlapping geomembranes on welded joints must lie flat and smooth. The offset between the transverse overlaps of the welds should not be less than 50 cm. Use special welding rods for geomembranes, which must be clean and free of contamination. For T-joints, patch the base material with a 300 mm x 300 mm patch, rounding the corners of the patch.

If buffing is required on joints, this should be done to remove surface wax and create a rough texture. The areas immediately adjacent to the membrane junction must be carefully treated. After treatment, the surface should remain clean. The edge of the upper geomembrane at the joint must be machined at an angle of 45°. Welds must be neat, aesthetically pleasing and free from slipping or lifting. Test welding conditions should be the same as production welding conditions. If any test weld fails the tensile or shear strength tests, all test welds must be redone.

7. Quality control of geomembrane welds

(1) Non-destructive testing

This is a leak test for suspicious areas.

(2) Double seam with double heat seal

Carry out a depressurization test: insert a special needle into the cavity of the double seam. Seal both ends and inflate to 250 kPa, then stop inflating and maintain pressure for two minutes.

After an initial two-minute stabilization period, monitor the air pressure for 10 minutes. If the pressure drop exceeds 10 kPa or the pressure becomes unstable, the weld is considered poor quality. If the pressure remains constant (pressure drop < 10 kPa), after testing, cut the opposite end of the test weld to check the integrity of the sealed channel. If there is no air leak, identify and mark the sealed area. If there is interlocking in the test seam, mark the location of the interlocking and test both sides of the interlocking separately.

Remove the needle or other air injection device. Repair the hole using extrusion welding or geomembrane splicing.

(3) Extruded single weld

Test equipment: vacuum chamber, vacuum pump, soap solution

Test procedure: Apply soap solution to the geomembrane weld. Place the vacuum chamber over the wetted weld surface, making sure the seal is tight. Then create a vacuum to the specified pressure (25 cmHg). Inspect the membrane for soap bubbles for at least 10 seconds. No bubbles means the test has passed; otherwise, note the location of the bubbles and repair as necessary. For welds not suitable for vacuum or air pressure testing, perform an electric spark test (approximately 10,000 volts). The weld is considered "passable" if no electrical spark is observed; otherwise repairs are required.

(4) Destructive testing

After the non-destructive testing, weld samples must be taken for tensile strength testing.

Sample dimensions: 0.3 m × 0.9 m

Test location and frequency: Testing is performed once per 60 m of weld length. Test locations should be determined during welding to ensure consistent testing of each weld.

Number of specimens: Six specimens shall be taken for tensile strength and shear strength testing (three specimens each).

Quality criteria: The weld's tensile and shear strength must exceed that of the base material to pass the test. Otherwise, additional specimens must be taken from the original weld for testing. If three consecutive specimens fail the test, the entire weld must be redone.

8. Repair of welded seams

We repair areas selected for destructive testing, individual non-compliant welds, and suspect areas as needed. We also apply patches when necessary. We put our clients' interests first and earn your trust through our dedicated service.