Geomembrane

1. Material Requirements

• The geomembrane (typically HDPE, LDPE, or PVC) must meet ASTM/GRI standards for thickness, tensile strength, and chemical resistance.

• Thickness: Minimum 1.0–2.5 mm (depending on design requirements).

• Testing: Factory pre-tests (e.g., puncture resistance, tear strength, and seam peel tests)

  must be conducted.

2. Subgrade Preparation

• The dam surface must be smooth, compacted, and free of sharp protrusions (e.g., rocks, roots, or debris).

• Any cracks or voids must be filled with fine-grained soil or mortar and re-compacted.

• A geotextile cushion layer (if specified) should be installed to protect the geomembrane.

3. Geomembrane Installation

• Unrolling & Alignment:

• Lay the geomembrane in the direction of least stress (usually parallel to the dam slope).

• Avoid excessive stretching or dragging to prevent damage.

• Anchoring:

• Secure the top edge into an anchor trench (min. depth 0.5–1.0 m).

• Use ballast (sandbags, gravel bags) on slopes to prevent wind uplift.

4. Seaming & Welding

• Methods:

• Dual Hot Wedge Welding (primary method for HDPE/LDPE).

• Extrusion Welding (for patches and complex areas).

• Seam Overlap: Minimum 100–150 mm (4–6 inches).

• Testing:

• Non-destructive (Air Pressure/Vacuum Test) for critical seams.

• Destructive (Peel & Shear Tests) on sample seams.

5. Quality Control & Inspection

• Visual Checks: No holes, wrinkles, or unbonded seams.

• Seam Integrity: 100% testing for large dams (random sampling for smaller projects).

• Repairs: Defective areas must be patched with overlap ≥ 150 mm beyond the damaged zone.

6. Protection & Covering

• Immediate Covering:

• Use geotextile or soil layers (min. 300 mm) to prevent UV degradation.

• For exposed applications, use UV-resistant geomembrane.

• Slope Stability:

• Avoid heavy machinery on unprotected geomembrane.

• Install erosion control mats if needed.

7. Safety & Environmental Compliance

• Workers’ Safety:

• Use non-slip footwear, harnesses (for steep slopes), and gloves.

• Environmental Protection:

• Prevent geomembrane scraps from entering waterways.

• Follow local regulations for material disposal.

8. Documentation & Handover

• Record welding parameters, test results, and repair logs.

• Submit as-built drawings showing geomembrane layout and seam locations.

Note: Adjustments may be needed based on dam type (embankment/concrete), climate, 

and design specifications (e.g., USACE, ICOLD guidelines).

Let me know if you need modifications for specific standards or additional details!