Which type of soils has a limitation concerning previous compaction during the Modified Proctor test?

Soils that have been previously compacted present particular challenges during the Modified Proctor test because the test measures the moisture-density relationship of soil for optimal compaction under controlled conditions. If a soil sample has already been compacted, it may not yield consistent or accurate results when subjected to the test again. This happens because previous compaction may alter the soil structure, density, and moisture condition, leading to a misinterpretation of the material’s properties.

For effective assessment during the Proctor test, it is essential that the soil being tested is in its natural, uncompacted state. This allows for the determination of the maximum dry density and optimum moisture content that can be achieved through compaction processes. Therefore, previously compacted soils cannot be effectively tested using this method, as their original properties may no longer be present.

The other soil types mentioned do not have the same limitation regarding prior compaction, which is specific to the potential variance in results from re-compacted materials during the testing process.