What is the required backfilling layer thickness when using loose earth for a water piping trench?

• A. 3-inch
• B. 4-inch
• C. 6-inch
• D. 8-inch

Answer: (C)

The requirement for a 6-inch backfilling layer thickness when using loose earth for a water piping trench is based on ensuring adequate support and protection for the piping. This thickness allows for proper compaction, which is essential to minimize settlement and prevent damage to the pipes from shifts in the soil over time. A 6-inch layer ensures that the soil can envelop the piping adequately, providing both stability and reducing the likelihood of infiltration from surrounding soils.

Using a thicker layer, such as 8 inches, may not be applied systematically or may result in additional compaction challenges due to the increased weight and volume of soil. Meanwhile, thinner options, like 3 or 4 inches, do not provide enough material to ensure the water pipes are securely surrounded by supportive backfill, potentially leading to issues like pipe collapse or misalignment. Therefore, the requirement for a 6-inch backfill layer strikes a balance between adequate support and practical excavation practices.