What tolerance must be met for the removal of plastic soils below the finished earthwork grade?

• A. +/- 1 inch
• B. +/- 12 inches
• C. +/- 3 inches
• D. +/- 6 inches

Answer: (D)

In earthwork, the tolerance for removal of plastic soils beneath the finished grade describes how close you must get to the target depth before you consider the task complete. Plastic soils, like clays, can vary in thickness and behavior under load and moisture, so field conditions aren’t perfectly uniform. A practical tolerance is used to accommodate that variability while still ensuring a stable subgrade.

The six-inch tolerance lets you account for measurement differences and natural soil variation without needing constant rework. It means the actual depth removed can be up to six inches deeper or up to six inches shallower than the specified depth, which provides a reasonable margin for field conditions while protecting the integrity of the finished grade.

Tighter tolerances, such as one or three inches, would be impractical in most jobs due to measurement error and soil variability. A much looser tolerance, like twelve inches, could leave excessive unsuitable material or create subgrade problems. So, six inches is the balanced, commonly accepted standard for this task. If removal exceeds the tolerance, adjustments or additional backfill and compaction are needed to meet the project specifications.