A tamping foot compactor does not adequately compact the upper 2-3 inches of a lift.

A tamping foot compactor does not adequately compact the upper 2-3 inches of a lift.

• A. They are typically well compacted
• B. They are often not adequately compacted
• C. They are unaffected by compaction
• D. They become overly compacted

Answer: (B)

The key idea is that a tamping foot delivers energy in a focused, vertical impact that effectively densifies a deeper portion of the lift, but it does not reliably consolidate the very top surface. The upper 2–3 inches aren’t always compacted well because the energy is absorbed and dissipated before it can uniformly close the surface air voids. As a result, the surface layer often remains looser, which is why finishing with a surface-oriented tool (like a plate compactor) is used to densify the top layer and prevent late settlement. This makes the statement that the upper portion is often not adequately compacted the best description.

The key idea is that a tamping foot delivers energy in a focused, vertical impact that effectively densifies a deeper portion of the lift, but it does not reliably consolidate the very top surface. The upper 2–3 inches aren’t always compacted well because the energy is absorbed and dissipated before it can uniformly close the surface air voids. As a result, the surface layer often remains looser, which is why finishing with a surface-oriented tool (like a plate compactor) is used to densify the top layer and prevent late settlement. This makes the statement that the upper portion is often not adequately compacted the best description.