Which best describes the recommended compaction approach for backfill material?

• A. Compact in large blocks
• B. Compact only once at the bottom
• C. Compact in small lifts
• D. Skip compaction near utilities

Answer: (C)

Compact in small lifts. When backfilling around buried utilities, you want to bring in material in thin layers and compact each layer before adding the next. This approach ensures the soil around the pipe or trench is densely packed all the way to the surface, reducing voids that can cause settlement or movement of the pipe. Small lifts allow you to apply consistent compaction around complex shapes and verify density as you go, which helps prevent differential settlement and damage to the utilities.

If you were to compact large blocks at once, dense pockets can form with voids beneath or around the conduit, making it difficult to achieve uniform support and increasing the risk of future settlement or pipe movement. Compacting only at the bottom ignores the layers above, leaving loose material that can settle later. Skipping compaction near utilities is dangerous because the area around pipes and other features needs tight, uniform compaction to provide stable support.

So, using small lifts is the best practice to achieve a stable, uniformly dense backfill around utilities.