A compaction curve typically plots which two variables?

A compaction curve plots dry unit weight versus moisture content because it is used to illustrate the relationship between the moisture content of soil and its dry density during the compaction process. This curve helps engineers determine the optimum moisture content at which the soil achieves its maximum dry density, which is crucial for understanding how the soil behaves under load and for ensuring adequate compaction in construction projects.

The dry unit weight is calculated by dividing the weight of the soil solids by the volume of the soil, excluding any moisture. By plotting this against moisture content, it allows for the analysis of how moisture affects the ability of soil to be compacted. As moisture content increases, the dry unit weight typically increases until it reaches a peak (the optimum moisture), after which further addition of water leads to a decrease in dry unit weight due to the saturation of voids and potential loss of structural integrity in the soil matrix.

This relationship is pivotal for civil engineering applications, particularly in construction and earthwork, as it informs the necessary compaction techniques and expected performance of the soil under structural loads. Other options do not represent the standard methodology for determining soil compaction characteristics as effectively as the dry unit weight versus moisture content does.