In the case of large stones or bedrock, what materials must be used to backfill the trench to grade?

• A. Sand, gravel or crushed stone that shall pass a 3/4-inch sieve.
• B. Portland cement and water.
• C. Pure topsoil.
• D. Concrete and asphalt.

Answer: (A)

When trench backfill encounters large stones or bedrock, you need a granular material that can be compacted around irregularities and still drain. The best choice is sand, gravel, or crushed stone that will pass a 3/4-inch sieve. This kind of material fills voids effectively, allows for good compaction, and permits drainage so water doesn’t pool around the pipe. It helps create a stable, grade-ready base that supports the surrounding rock and reduces the risk of settlement.

Using Portland cement and water would create concrete, which is rigid and can transfer stresses to the pipe rather than allowing for movement and drainage. Pure topsoil can contain organic matter and settle unevenly, leading to voids and poor support. Concrete and asphalt are also too rigid for backfill and aren’t appropriate around piping.