Why do we use a modified proctor rather than a standard proctor?
Standard proctor and modified proctor are tests designed to emulate soil compaction. Based on the specifications of the project, the firm testing the soil would run either of the test.
Relatively higher energy is applied in modified proctor tests compared to standard, thus yielding higher unit weight of the soil.
If the project requires a higher bearing capacity or stiffer soil, more energy is applied to soil in order to achieve better compaction. Therefore it is upto the project civil engineer to determine what specifications are needed to achieve a specified outcome.
Township/local governing bodies also have specifications which need to be achieved for roads, commercial buildings and related infrastructure. This is another determining factor in soil compaction.