In which zone is the 12-inch maximum layer thickness applied?

In which zone is the 12-inch maximum layer thickness applied?

• A. Cover Zone
• B. Bedding Zone
• C. Top Zone
• D. Lowest Zone

Answer: (C)

The main idea here is that lift thickness is controlled by the function and compaction needs of each zone in the fill. The top zone is the portion of the embankment or filled layer near the surface that will form the finished surface, so it’s limited to a 12-inch maximum lift. Keeping lifts to this thickness helps ensure the soil can be compacted evenly throughout the layer, producing uniform density, reducing voids, and preventing surface defects or uneven settlement as traffic loads are applied. In this scheme, the other zones refer to deeper portions of the fill that have different purposes and are compacted under different conditions, so their lift limits aren’t the same as the top zone. Choosing the top zone for the 12-inch maximum lift aligns with the goal of achieving a stable, well-compacted surface layer.

The main idea here is that lift thickness is controlled by the function and compaction needs of each zone in the fill. The top zone is the portion of the embankment or filled layer near the surface that will form the finished surface, so it’s limited to a 12-inch maximum lift. Keeping lifts to this thickness helps ensure the soil can be compacted evenly throughout the layer, producing uniform density, reducing voids, and preventing surface defects or uneven settlement as traffic loads are applied.

In this scheme, the other zones refer to deeper portions of the fill that have different purposes and are compacted under different conditions, so their lift limits aren’t the same as the top zone. Choosing the top zone for the 12-inch maximum lift aligns with the goal of achieving a stable, well-compacted surface layer.