What types of soils can be used in Modified Proctor tests?

The Modified Proctor test is designed to determine the optimum moisture content and maximum dry density of soil for compacted fills and earthworks. The type of soils suitable for this test generally include granular and cohesive soils that have a particle size distribution appropriate for compaction.

Soils that have 30% or less of their particles retained on the ¾" sieve are effectively within the range where the Modified Proctor test is applicable. This limitation allows for the proper assessment of moisture-density relationships, as larger particles (those retained on the ¾" sieve) can lead to less effective compaction and skew results.

In contrast, soils with more than 30% of their particles retained on the ¾" sieve might not compact uniformly, and their larger particle sizes could result in voids that prevent achieving an accurate density measurement. Additionally, clay-based soils can be used, provided they meet the particle size criteria, but they are not the sole candidates for the test. Thus, focusing on soils that meet the specified sieve criteria ensures reliable testing outcomes.