What minimum density of the Modified Proctor maximum density as determined by FM 1 T-180 should be obtained within the entire limits of the width and depth of the areas to be stabilized?

• A. 95%
• B. 96%
• C. 98%
• D. 99%

Answer: (C)

The key idea here is how field compaction is measured against a lab-established standard. The Modified Proctor test (FM 1-T-180) provides a maximum dry density for the soil mix at an optimum moisture content. In the field, the in-place dry density must reach a specified fraction of that lab maximum across the entire area to be stabilized. Requiring a high, uniform percentage ensures the stabilized surface has enough bearing capacity, low plasticity and low permeability, and predictable performance under loads and moisture changes. For stabilization projects, that uniform target is 98 percent of the Modified Proctor maximum dry density, evaluated over the whole width and depth of the area. So the correct requirement is to achieve at least 98 percent of the lab maximum across the entire area.