In trench backfill compaction, which backfill should be compacted if native soil is used and is relatively dense?

• A. lower backfill
• B. upper backfill
• C. middle backfill
• D. outer backfill

Answer: (B)

When the native soil is dense, the bottom portion next to the pipe already has good density and support, so you don’t need to spend effort compacting it further. The priority is to achieve a stable, well-supported surface that will carry loads and minimize settlement. Compacting the upper backfill accomplishes this, helping to meet compaction specs and reduce surface settlement, while the dense native soil below provides the necessary bearing capacity without additional compaction. Overworking the lower layer can also risk disturbing the pipe or causing unwanted settlements, so the upper backfill is the focus for compaction in this scenario.