Why Is Installation Technique So Important?
Long service life of HDPE and corrugated pipes depends largely on correct installation technique. Wrong trench dimensions or insufficient backfill compaction leads to uneven load distribution and long-term deformation.
Trench Dimensions: Width and Depth
- Minimum trench width: Pipe outside diameter (OD) + minimum 200mm on each side
- For Ø200 pipe: ~600mm trench width
- For Ø500 pipe: ~900–1000mm trench width
- Minimum laying depth: At least 700–800mm from pipe crown to ground surface (minimum 1000mm with vehicle traffic)
Bedding Material: What to Use?
- Sand (0–2mm): Ideal bedding material.
- Mixed sand-gravel (0–32mm): Economical option for large diameter pipes.
- Crushed stone (0–22mm): Usable but may require fine sand coating.
- Do not use: Hard rock fragments, organic material, frozen ground, clay soil.
Bedding thickness should be minimum 100–150mm under the pipe.
Backfill and Compaction Stages
- Stage 1 (Bedding): Pipe is placed on prepared bedding. No voids should remain under the pipe.
- Stage 2 (Haunch fill): Filled with sand up to pipe centreline, compacted every 150–200mm.
- Stage 3 (Initial backfill): Continue with same fine material up to 300mm above pipe crown.
- Stage 4 (Main backfill): Excavated soil can be used if suitable; compacted in 300mm layers.
Important: Vibratory plate compactor should not be used without minimum 300mm cover over the pipe.
What to Do with Groundwater?
If there is water in the trench, it must be pumped out before pipe installation. For empty pipes, anti-flotation weight or anchoring measures may be needed against buoyancy forces.