HDPE Membrane Impermeability Construction Plan for Landfills

Chapter 1: Substrate Requirements

1. Prior to the installation of HDPE geomembrane, a comprehensive inspection of the underlying foundation shall be conducted in coordination with the civil engineering contractor, the supervising engineer, the design team, and the owner. Construction may proceed only after confirming compliance with design requirements, meeting all construction conditions, and completing the handover inspection record.

2. The quality of the base surface shall comply with the design requirements: the bottom and slope surfaces of the excavation, their slope ratios, anchor slots on the slopes, and the junctions between the slope surface and the facing surface, as well as the base surface of the silo wall concrete structure, must all strictly meet the design specifications.

3. The base surface shall be dry, compacted, and smooth, free of cracks, obvious protrusions, mud, and depressions. Within a vertical depth of 25 mm, it shall be free of tree roots, debris, gravel, rebar ends, and glass fragments. Its flatness shall vary smoothly within the permissible tolerances, with a uniform and consistent slope.

4. At internal and external corners on the base surface, ensure smooth transitions; the column bases shall be formed into rounded arcs.

5. The substrate surface shall be dry, with a moisture content preferably below 15%.

6. The subgrade shall be compacted and uniform, with a dry density of no less than 1.4 t/m² for soil subgrades.

7. After the civil engineering, supervision, design firms, the owner, and the general contractor have inspected and signed off in approval, earthwork geomembrane installation may proceed.

Chapter 2: Climatic Requirements for Construction

1. Ambient temperatures should generally be above 5°C; at low temperatures, the geomembrane should be tensioned more tightly, while at high temperatures, it should be relaxed.

2. Wind force is below level 4.

3. When temperatures are excessively low, construction should generally be avoided during winds of Force 4 or higher and in rainy or snowy conditions.

4. During windy conditions, when wind forces may affect geomembrane installation, the HDPE geomembrane to be welded shall be securely weighted down with sandbags.

Chapter 3: Installation of HDPE Liners

1. Prior to the installation of HDPE geomembrane, corresponding qualified acceptance documentation from the civil engineering works shall be provided.

2. Prior to cutting HDPE membrane, its relevant dimensions should be measured accurately, and the material should be cut according to the actual measurements. It is generally not advisable to cut based on the dimensions shown in the drawings; instead, each sheet should be numbered individually, with detailed records kept on a dedicated form.

3. When installing HDPE geomembranes, strive to minimize the number of welds and, while ensuring quality, maximize material savings. This approach also facilitates quality assurance.

4. The overlap width of joints between membranes shall generally be no less than 10 cm; typically, the weld seams are arranged parallel to the direction of maximum slope, i.e., along the slope.

5. Typically, at corners and in areas with irregular geometry, the length of joints should be minimized. Unless otherwise specified, on slopes steeper than 1:6, welds should be avoided within 1.5 meters of the crest or in regions of stress concentration.

6. During installation, HDPE geomembranes should be laid without artificial wrinkles; at lower temperatures, they should be stretched tightly and smoothed as much as possible.

7. After the HDPE geomembrane has been laid, minimize walking on the membrane surface and handling tools. Any objects that could potentially damage the HDPE membrane must not be placed on it or carried while walking on it, to prevent accidental damage.

Chapter 4: Welding of Geomembranes

1. The hot‑wedge welding process consists of the following steps: adjusting the pressure, setting the temperature, setting the speed, inspecting the weld overlap, loading the film into the machine, starting the motor, and applying pressure to perform the weld.

2. The joints must be free of oil and dust, and the overlapping surfaces of the HDPE geomembrane shall not contain any foreign matter such as sand or debris; if such contaminants are present, they must be thoroughly removed prior to welding.

3. At the start of each day’s welding operations, a test weld must be performed on-site using a 0.9 mm × 0.3 mm specimen, with an overlap width of at least 10 cm. The specimen shall then undergo peel and shear tests on the testing machine at the site. Only after the test specimen passes may full‑scale welding proceed using the speed, pressure, and temperature settings that were adjusted at that time. The date, time, and ambient temperature must be clearly marked on the test specimen. During operation, the hot‑wedge welder must continuously monitor its performance and make fine adjustments to speed and temperature as needed to suit the specific site conditions.

4. Welds shall be neat and aesthetically pleasing, with no slippage or skipping defects.

5. When the geomembrane length is insufficient, longitudinal splicing is required. First, weld the transverse seams, then weld the longitudinal seams. Transverse seams that are spaced more than 50 cm apart shall be arranged in a T‑shape and must not intersect in a cross pattern.

6. Adjacent geomembrane seams should be lapped with staggered joints whenever possible. The junctions formed between membrane panels shall be T‑shaped, and cross‑shaped joints should be minimized. At the intersections of longitudinal and transverse welds, reinforcement using an extrusion welder is recommended.

7. During welding, no permanent creases shall be allowed. When installing HDPE geomembranes, account for the thermal expansion and contraction caused by local temperature fluctuations, and provide adequate overlap allowances in accordance with the material’s performance requirements.

8. When the temperature displayed by the handheld welder’s temperature control falls below 200°C, use a clean cloth or cotton gauze to gently wipe away any debris before welding; if necessary, re‑grind the surface. Never wipe it with your hands.

9. When condensation, moisture, or dirt is present at the joint, address these issues before proceeding with welding.

10. Welding shall not be performed during rainfall or when the joint is damp, covered with dew, or contaminated with coarse sand, unless appropriate protective measures are in place.

11. When the temperature is below 5°C, construction shall not be carried out in accordance with the relevant specifications. If construction must proceed, the welding machine shall be preheated prior to welding.

12. During the welding process, the extrusion welder should regularly inspect the slider on the welding gun; if wear is severe, the slider should be replaced promptly to prevent damage to the membrane surface.

13. During welding, the geomembrane should be powered by a generator with stable voltage regulation; in special circumstances when using local grid power, a voltage stabilizer must be employed.

Chapter 5: Anchoring of HDPE Membranes

1. There are three methods of anchoring: groove anchoring, nail‑gun anchoring, and expansion bolt anchoring; in most cases, groove anchoring is used.

2. When using trench anchoring, depending on the service conditions and stress state of the HDPE geomembrane, the width of the anchoring trench is generally not less than 0.5 m to 1.0 m, and its depth shall not be less than 0.5 m to 1.0 m.

3. When using nail‑gun anchoring, the width of the cleat shall be no less than 2 cm, and its thickness shall be no less than 2 mm. The spacing between nails shall not exceed 400 mm, and exposed portions of the cleat shall be provided with corrosion‑preventive measures.

4. When using expansion bolts for anchoring, the bolt diameter shall be no less than 4 mm, and the spacing between bolts shall not exceed 0.5 m. During installation, first secure the membrane in its designated position with prepared sandbags to prevent strong winds from blowing it out of place, and then proceed with the expansion‑bolt anchoring.

Chapter 6: Precautions for Geomembrane Construction

1. Electrical equipment and power supply lines shall comply with the relevant professional standards.

2. During operation, the power cords of heat guns, grinders, and welders must be kept as far away as possible from their working areas to prevent damage to the cords and potential electrical leakage.

3. Except during hot-air welding, the nozzle of the heat gun must never come into contact with the HDPE membrane surface under any circumstances and should be kept as far away as possible from the membrane surface, personnel, machinery, and other objects.

4. When not in use, the welding machine must not be placed directly on the HDPE membrane surface; it should be positioned on a support frame or secured with sandbags.

5. After use, the film-cutting knife should be immediately returned to its blade holder.

6. All temporary small tools used on site shall be promptly returned to the tool box after use.

7. It is strictly prohibited to dispose of solder material removed from the welding gun tip of the extrusion welder directly onto the geomembrane surface.

8. When working in hazardous areas such as the edges of steep slopes, workers must wear safety harnesses and hard hats.

9. Smoking is prohibited at the HDPE geomembrane construction site, and fire‑fighting equipment must be provided. Footwear with metal nails or high‑heeled hard‑soled shoes is not permitted on the membrane surface, and any activity that could damage the finished geomembrane is strictly forbidden.

Chapter 7: Testing and Repair of Finished Geomembranes

1. Welding operators shall mark the test specimens and the welds being performed with the welder’s name and the welding time.

2. During the construction process, a construction log shall be maintained by the project manager or the site foreman.

3. The inspection is conducted in three steps: visual inspection, pneumatic testing, and destructive testing.

4. Visual inspection primarily involves a thorough examination of the geomembrane’s appearance, weld quality, T‑joint welds, and any debris on the substrate; all construction personnel must adhere to this procedure throughout the entire construction process.

5. In addition to visual inspection, all welds shall be subjected to vacuum testing for leak tightness; areas where vacuum testing is not feasible shall undergo even more rigorous self‑inspection.

6. The inflation pressure for the air‑tightness test is 0.25 MPa, with no leakage over a 5‑minute period. Given that the membrane material is relatively soft and prone to deformation, a pressure drop of up to 20% is permissible.

7. When conducting tensile tests on test coupons taken from double‑track welds, the acceptance criterion is that, during peel and shear testing, the weld itself remains intact while only the base metal is fractured. If this criterion is met, the weld is deemed acceptable. If the test coupon fails to meet the requirement, a second coupon shall be taken from the same weld. Should all three consecutive coupons fail, the entire weld must be reworked.

8. Qualified test specimens shall be submitted to the owner, the general contractor, and relevant parties for archival purposes.

9. Defects identified during visual inspection, pneumatic testing, and destructive testing shall be repaired promptly. If immediate repair is not feasible, appropriate markings must be applied to prevent oversight during subsequent repairs.

10. During visual inspection, if defects such as pinholes or tears are detected on the membrane surface, or if issues like incomplete welds, false welds, or damage occur during the welding process, these areas shall be promptly repaired using fresh base material, with the repair patch extending 10–20 cm beyond each side of the damaged area. Records must also be kept.

11. For repaired welds, a detailed visual inspection is generally required to verify the integrity of the repair before release.