Drainage Maintenance

Module 3: Drainage Maintenance

1. Importance of Drainage in Highways

Effective drainage is critical to highway longevity and safety:

• Prevents Water Damage: Standing water weakens pavement layers, leading to potholes and subsidence.

• Reduces Ice Hazards: Poor drainage increases winter ice formation.

• Avoids Flooding: Blocked systems cause surface water accumulation, increasing hydroplaning risks.

• Protects Subgrade: Saturated soil loses load-bearing capacity, causing structural failure.

• Compliance: Meets Design Manual for Roads and Bridges (DMRB) standards (e.g., CD 535 for drainage).

Consequences of Neglect:

• Accelerated road deterioration (e.g., edge breakage, rutting).

• Higher long-term maintenance costs.

2. Identifying Blocked or Damaged Drainage Components

A. Common Drainage Elements

B. Inspection Techniques

• Visual Checks:

• Gullies: Remove grates; check sediment >25% depth.

• Culverts: Look for cracks, rust (metal), or spalling (concrete).

• CCTV Surveys: Camera inspections for underground pipe blockages.

• Dye Testing: Trace water flow to locate leaks or misconnections.

• Hydraulic Testing: Measure flow rates to detect restrictions.

C. Defect Prioritization

• Immediate Action: Total blockages causing flooding.

• Scheduled Repair: Partial blockages or minor cracks.

3. Cleaning and Jetting Techniques

A. Mechanical Cleaning

• Gully Emptying:

• Vacuum tankers remove silt/debris (target 95% clearance).

• Safety: Confined space entry protocols (if manual cleaning).

• Ditch Clearing:

• Excavators or backhoes for large-scale silt removal.

• Slope reprofiling to restore 1:3 gradient (DMRB CD 528).

B. High-Pressure Jetting

• Equipment: 1,500–3,000 psi jetter units with rotating nozzles.

• Procedure:

1. Flush pipes to loosen debris.

2. Follow with vacuum extraction.

• Best For: Grease/fine sediment in culverts or pipes ≥150mm diameter.

C. Eco-Friendly Methods

• Bioaugmentation: Enzyme treatments break down organic blockages.

• Silt Traps: Install filters to reduce maintenance frequency.

4. Repairing and Replacing Drainage Components

A. Minor Repairs

• Gully Grates: Straighten bent frames; replace broken bars.

• Pipe Patching:

• Cured-in-Place Liner (CIPP): Resin-coated tube inserted and hardened.

• Spray Lining: Cementitious coating for corrosion protection.

B. Major Replacements

• Culvert Renewal:

• Open-Cut: Excavate and replace (disruptive but cost-effective).

• Trenchless: Pipe bursting or slip-lining for minimal surface impact.

• Channel Reconstruction:

• Geotextile lining to prevent erosion.

• Check dams to slow water flow in steep areas.

C. Material Selection

D. Safety & Compliance

• Excavations: Shoring/trench boxes per Construction (Health, Safety and Welfare) Regulations 1996.

• Discharge: Silt-laden water must be treated before release (Environmental Permitting Regulations).

Key Takeaways

• Proactive Inspections: Detect issues early (e.g., silt buildup >50mm requires action).

• Right Technique: Jetting for pipes; mechanical cleaning for gullies.

• Material Matters: HDPE for corrosion-prone areas; concrete for heavy loads.

Practical Training Ideas:

• Field Exercise: Use CCTV footage to diagnose a blocked culvert.

• Demo: Compare jetting vs. rodding for a simulated pipe blockage.