Because double drum compactors compact from top to bottom, what lift depth is recommended?

Because double drum compactors compact from top to bottom, what lift depth is recommended?

• A. 2 inches
• B. 4 inches
• C. 6 inches
• D. 4 inches or less

Answer: (D)

Lift depth controls how much material is compacted in each pass, and with double drum compactors the action is from the top down. Keeping lifts shallow allows the top portion to be fully compacted before the roller presses into lower layers, producing uniform density and a smoother, more stable surface. If the lift is too deep, the top layer may not densify properly in one pass, leading to surface defects, rutting, or the need for extra passes. That’s why the recommended depth is four inches or less—the option that encompasses common shallow lifts like two and four inches.

Lift depth controls how much material is compacted in each pass, and with double drum compactors the action is from the top down. Keeping lifts shallow allows the top portion to be fully compacted before the roller presses into lower layers, producing uniform density and a smoother, more stable surface. If the lift is too deep, the top layer may not densify properly in one pass, leading to surface defects, rutting, or the need for extra passes. That’s why the recommended depth is four inches or less—the option that encompasses common shallow lifts like two and four inches.