An operator is backfilling a trench that contains a newly installed 600 mm diameter water main. The trench is 2.5 m deep and 1.2 m wide. What is the primary concern when selecting backfill material and compaction technique for the initial layer over the pipe?

Question: An operator is backfilling a trench that contains a newly installed 600 mm diameter water main. The trench is 2.5 m deep and 1.2 m wide. What is the primary concern when selecting backfill material and compaction technique for the initial layer over the pipe?

Answer options:

• Ensuring the backfill material consists solely of large aggregate to promote drainage. ✅ Preventing damage to the pipe by using granular material free of large rocks and compacting gently.
• Maximizing the speed of backfilling by using the largest bucket available and dumping a full load.
• Achieving the highest possible compaction density immediately, regardless of material type.

Correct answer: Preventing damage to the pipe by using granular material free of large rocks and compacting gently.

Explanation: When backfilling over a newly installed pipe, the primary concern is to prevent damage to the pipe itself. This is achieved by using granular material free of large rocks and compacting gently in layers to avoid point loads that could stress or break the pipe. Large aggregate can damage the pipe, and dumping a full load can cause impact damage or uneven settlement.