During backfilling of a trench over a newly installed pipe, what is the 'initial backfill' stage, and what material is typically used?

Question: During backfilling of a trench over a newly installed pipe, what is the 'initial backfill' stage, and what material is typically used?

Answer options:

• Placing large rocks and debris directly over the pipe for stability. ✅ Hand-placing approved granular material, free of large stones, up to 300 mm above the pipe's crown.
• Filling the entire trench with native material using heavy machinery.
• Applying a layer of geotextile fabric directly on the pipe.

Correct answer: Hand-placing approved granular material, free of large stones, up to 300 mm above the pipe's crown.

Explanation: The initial backfill stage, often called 'haunching' and 'initial cover', involves carefully placing approved, free-draining granular material by hand or light equipment around the pipe haunches and up to at least 300 mm (typically 300-450mm) above the pipe's crown. This protects the pipe from damage during subsequent compaction and ensures uniform support, as detailed in municipal and CSA B182.X standards.