Geomembrane Applications in Tunnel Waterproofing: Materials, Installation, and Quality Control

Material Selection

• Primary Material: High-Density Polyethylene (HDPE) geomembrane

• Chemical/UV resistance (≥20-year UV stability)

• Impermeability: <10⁻¹² cm/s (ASTM D5887)

• Tensile strength: ≥25MPa (ASTM D6693)

• Thickness: 1.0–2.0mm

• Width: 4–6m (customizable for tunnel cross-sections)

• Key Properties:

Installation Process

1. Pre-Installation Preparation

• Surface Treatment:

• Achieve ≤3mm/m² flatness on primary lining

• Seal leaks with grouting or drainage boards

• Tool Preparation:

• Hot wedge welders (for HDPE)

• Hot air guns (for detail work)

2. Laying Procedure

• Sequence: Crown → sidewalls → invert (top-down)

• Welding Standards:

• Dual-track seams: 100mm width

• Seam strength: ≥80% parent material

• Testing: 100% vacuum/pressure testing at 0.2MPa

3. Anchoring System

• Mechanical Fixing:

• Expansion bolts @ 0.6–1.0m spacing

• Load capacity: ≥1.5kN per anchor

4. Critical Detail Treatment

• Corners: Pre-fabricated inserts with 150% overlap

• Movement Joints: Install waterstops + 200mm extra membrane slack

Quality Assurance

1. Material QC

• Batch testing for:

• Thickness tolerance: ±0.1mm

• Peel adhesion: ≥6N/mm

2. Construction Monitoring

• Real-time checks for:

• Wrinkling: ≤5mm/m tolerance

• Seam continuity: No visible gaps under 10x magnification

3. Post-Installation Protection

• Mandatory measures:

• Protective boards during secondary lining

• No hot works within 3m of membrane

Advantages & Limitations

√ Benefits:

• Waterproofing efficiency: Blocks 99.9% hydrostatic pressure

• Construction speed: 200–300m²/day installation rate

• Durability: 50+ year service life in buried conditions

× Challenges:

• Puncture vulnerability: Requires geotextile underlay in rocky strata

• Deformation sensitivity: Limited to ≤3% substrate strain

Title: "HDPE Geomembranes for Tunnel Waterproofing: Technical Standards and Field Practices"

Key Metrics:
▸ Leakage Rate:<0.1L/m²/day (EN 1928)
▸ Cost Efficiency: $15–25/m² installed
▸ Temperature Range: -30°C to +60°C

Best Practices:
✔ Pre-construction mockups for weld parameter calibration
✔ Robotic welding for crown sections (>8m diameter tunnels)
✔ IoT-based monitoring for long-term integrity assessment

Compliance Standards:

• ITA-AITES Guidelines for Underground Structures

• ASTM D7867 - Geomembrane Seam Evaluation