Application of Drainage Boards in Tunnel Construction

1. Pre-Construction Preparation

• Material Inspection:
  Verify drainage board specifications (thickness, permeability ≥10⁻² cm/s) and check for physical damage.

• Tool Preparation:
  Prepare specialized laying equipment, cutting tools, and anchoring materials (e.g., HDPE fixing pins).

• Subgrade Treatment:
  Achieve surface flatness (≤3mm/m² deviation) and remove protrusions (>2mm height).

2. Drainage Board Installation

• Positioning & Layout:

• Install along tunnel sidewalls and invert with 0.5-1% gradient toward collection points.

• Maintain ≤5mm/m longitudinal wrinkling tolerance.

• Connection Methods:

• Overlap: Minimum 100mm overlap with seam sealing tape (peel strength ≥6N/cm).

• Thermal Welding: For HDPE boards, use 180-220°C wedge welders at 0.8-1.2m/min speed.

• Detail Processing:

• At corners: Custom-cut boards with 150% increased fastener density.

• At expansion joints: Allow 5-8% elongation capacity.

3. System Integration

• French Drain Interface:

• Embed board ends 300mm into drain trenches with bentonite waterstop.

• Pipe Connections:

• Install geotextile-wrapped intake headers (orifice size ≤5mm) at 15-20m intervals.

4. Protection & Backfilling

• Protective Measures:

• Cover with 400g/m² nonwoven geotextile before subsequent construction.

• Prohibit equipment (>2kPa ground pressure) directly over boards.

• Backfill Protocol:

• Use well-graded aggregates (4-20mm) in 200mm compacted lifts (≥95% Proctor).

5. Quality Assurance

• Visual Inspection:

• Reject installations with >3% wrinkled area or unsealed seams.

• Performance Testing:

• Conduct 24hr inflow tests (design capacity: ≥5L/min per linear meter).

• Documentation:

• Submit mill test reports (ASTM D4716), as-built drawings, and pressure test records.

Title: "Tunnel Drainage Systems: Best Practices for Drainage Board Implementation"

Key Metrics:
✔ Flow Efficiency – Maintains 85-90% of theoretical drainage capacity
✔ Construction Speed – 200-300m²/day installation rate
✔ Durability – Withstands 100+ kPa hydrostatic pressure

Critical Details:
▸ Anchoring: Stainless steel fasteners @ 0.5m grid (sidewalls) / 1m grid (invert)
▸ Transition Zones: Reinforce with composite drainage mats at T-junctions

Applications:

• Road/rail tunnels

• Underground stations

• Mining adits