What is the purpose of water in the Proctor test for soil density?

The Proctor test is a standard method used to determine the optimal moisture content at which a specific soil type will achieve its maximum dry density. Water plays a critical role in this process by providing lubrication, allowing soil particles to move closer together and rearrange into a denser configuration when compacted. When the moisture content is appropriate, the water helps fill the gaps between particles, reducing the amount of air space and allowing for greater compaction.

This increase in density through lubrication is essential because if the soil is either too dry or too wet, the results will not accurately reflect the soil's maximum density. Proper moisture content is crucial for achieving the desired compaction, thereby ensuring that the test results are reliable for engineering and construction applications.