When backfilling trenches, what is the recommended maximum depth of individual backfill layers?

• A. 3 inches
• B. 6 inches
• C. 12 inches
• D. 18 inches

Answer: (B)

The recommended maximum depth of individual backfill layers is 6 inches because this depth allows for better compaction and reduces the risk of settling after the trench has been backfilled. When layers are limited to this depth, it ensures that each layer can be adequately compacted using mechanical means or by hand. Compaction is critical to prevent voids and future ground movement, which can affect surface stability and the integrity of structures above.

Using layers that are too thick can lead to difficulty in achieving proper compaction, as the weight and pressure applied may not adequately compress the material. This may result in an uneven settlement or even cause damage to surrounding utilities and structures. Therefore, following the recommended maximum depth of 6 inches helps to minimize these issues and ensure a stable backfill environment.