Module 3: Drainage and Utilities Installation 

1. Types of Drainage Systems

Surface Water vs. Foul Water Drainage

Pipes, Gullies, and Manholes

• Pipes:

• Material Types: PVC (lightweight), clay (durable), concrete (heavy-duty).

• Gradients: Must slope 1:40 to 1:80 for proper flow.

• Gullies:

• Collect water from surfaces and filter debris.

• Fitted with gratings and silt traps.

• Manholes:

• Allow access for inspection and cleaning.

• Spaced every 30–50m depending on pipe size.

2. Laying Underground Utilities

Water, Gas, and Electrical Conduits

Safe Digging Practices (Avoiding Strikes)

• Before Digging:

• Check utility maps (Dial Before You Dig services).

• Use Cable Avoidance Tools (CAT) & Genny for detection.

• During Digging:

• Hand-dig near marked utilities (no mechanical excavation).

• Expose pipes/cables carefully before continuing.

• After Digging:

• Report damage immediately (even minor nicks).

3. Testing and Backfilling

Pressure Testing Pipelines

• Water Pipes:

• Filled with water and pressurized 1.5x working pressure for 1 hour.

• No drop in pressure = Pass.

• Drainage Pipes:

• Air or water test to check for leaks.

• Smoke testing for foul drains (identifies cracks).

Compaction Methods

• Layered Backfilling:

• 300mm layers compacted to 95% Proctor Density.

• Compaction Equipment:

• Vibratory Plates (for small trenches).

• Rollers (for large areas).

• Material Choices:

• Granular fill (best for drainage).

• Clay (needs heavy compaction).

Conclusion

This module ensures proper drainage design, safe utility installation, and leak-proof testing—critical for long-term infrastructure stability. The next module covers foundations and substructures.