A highway embankment is being constructed of lowplasticity clay (CL) whose natural moisture content is slightly below the standard AASHTO optimum. Specifications require the use of a tamping foot roller for compaction.

However, the roller being used does not always

“walk out” as compaction proceeds, and even when it does, it often fails to produce the required soil density.

The contractor and the project engineer disagree over appropriate corrective measures. The contractor wants to increase the weight of the roller by adding more ballast, thus increasing the contact pressure of the roller feet. The project engineer disagrees and suggests that the weight of the roller is adequate and that the foot size should be increased. Which recommendation is more nearly correct? Why?