What is the primary difference between the standard proctor and the modified proctor?

The primary difference between the standard proctor and the modified proctor lies in the amount of energy applied during the compaction process. The modified proctor involves a significant increase in the laboratory pounding energy, as it uses a heavier tamper and more layers of soil to be compacted, often at a greater drop height of the tamper. This additional energy allows for higher densities to be achieved compared to the standard proctor test.

In contrast, the standard proctor uses a lighter tamper and applies less energy which leads to lower maximum dry density values. While the modified proctor test is designed for soils that will undergo heavier loads or are used in applications where higher compaction is necessary, the standard test typically suffices for lighter applications and less demanding conditions. The differences in water content and other factors are secondary to the energy applied, which is what distinctly characterizes the modified test from the standard. This increased energy is crucial for achieving a denser, more stable soil structure under various conditions.