What is the primary purpose of bedding and backfill for building drainage trenches?

• A. To provide stable support for the pipe and maintain alignment.
• B. To increase water infiltration.
• C. To reduce soil fertility.
• D. To prevent any drainage.

Answer: (A)

The main idea is to provide a stable, protective cradle for the pipe so it stays in the right position. Bedding gives the pipe a smooth, level bottom and spreads the load so the pipe isn’t crushed or bent by surrounding earth. Backfill then surrounds the pipe, helping to resist movement from soil or traffic and keeping the pipe aligned as the trench settles. Together, they prevent shifting or deformation and keep the drainage system functioning correctly. They aren’t there to increase water infiltration, alter soil fertility, or stop drainage—their purpose is structural support and maintaining proper alignment.