If stone larger than one inch is present or bedrock is encountered, the trench shall be excavated to a depth at least how many inches below the grade elevation?

If stone larger than one inch is present or bedrock is encountered, the trench shall be excavated to a depth at least how many inches below the grade elevation?

• A. 6 inches.
• B. 3 inches.
• C. 1 inch.
• D. 12 inches.

Answer: (B)

When hard material such as stones larger than an inch or bedrock is present in a trench, the trench must go below the finished grade far enough to create a stable bedding plane for the pipe. The minimum depth allows space to place bedding material and to backfill and compact around the pipe so the load is carried evenly and the pipe isn’t affected by surface stones or uneven rock underneath. That’s why three inches below the grade elevation is specified—the smallest amount that reliably provides a proper bedding and backfill zone without needing excessive digging. Deeper depths (six or twelve inches) go beyond what is required for typical bedding, and too little (one inch) wouldn’t leave room for proper bedding and compaction.

When hard material such as stones larger than an inch or bedrock is present in a trench, the trench must go below the finished grade far enough to create a stable bedding plane for the pipe. The minimum depth allows space to place bedding material and to backfill and compact around the pipe so the load is carried evenly and the pipe isn’t affected by surface stones or uneven rock underneath. That’s why three inches below the grade elevation is specified—the smallest amount that reliably provides a proper bedding and backfill zone without needing excessive digging. Deeper depths (six or twelve inches) go beyond what is required for typical bedding, and too little (one inch) wouldn’t leave room for proper bedding and compaction.