Compaction of soils is engineeringly controlled by the use of compaction curves as determination by the Modified or Standard Proctor laboratory tests. These are part of a system called end-product methods.
Other called procedural methods are also frequently used to control compaction by the number of passes of a compactor per specified lift heights. Tests fills can be used to determine the minimum number of passes need to achieve the specified minimum dry density with varying moisture contents for the same soils intended to be used during production.
Proctor tests:
The compaction curves of soils are based on a specific input energy to the soil layers in the laboratory. They are not plainly called the maximum density of the soil. The are the maximum density of the soil for a certain input energy. Input energies greater than the modified proctor are most likely used in the field during heavy civil construction. Some construction specifications have even used 100 percent maximum dry density as a minimum threshold.
Soil compaction curves as determined from laboratory Proctor tests are plotted with dry density versus moisture content. Fine-grained soils such as clays are more influenced by changes in moisture than coarse-grained soils and thus develop more classically “defined” compaction curves.

If it is stated in the specifications that the soil is to be compacted to 95% of maximum dry density and within plus or minus 2 % of the optimum moisture content, such requirements are shown. This represents a minimum standard. For less critical jobs, a compliance window can be developed based on the specifications. But for larger jobs or where there’s more soil variability, for example from a natural borrow source, then a family of curves (FOC) will need to be developed. The FOC will follow the slope of the ZAV line for larger or smaller maximum dry densities. Therefore, a family of compaction curves will need to be developed for each soil type at the project. Each curve should also have companion gradation (including hydrometer) and plasticity tests completed so they can be correlated to the properties of the soils (or soil classification).
