The trench shall be backfilled in 6" layers to how many inches above the top crown of the piping?

• A. 18"
• B. 12"
• C. 24"
• D. 30"

Answer: (A)

Backfilling a trench around piping is done in small, controlled lifts so the soil can be properly compacted and the pipe remains protected from settlement or movement. The standard practice is to place backfill in 6-inch layers up to a height of 18 inches above the top of the pipe crown. This provides enough cover to resist surface loads and allows uniform compaction around the pipe, reducing the chance of voids or differential settlement. After reaching that 18-inch height, you continue backfilling in larger lifts to bring the trench to grade.

Choosing a smaller height wouldn’t give enough protection and compaction around the pipe, while larger heights aren’t the specified method and add unnecessary work.