What is a common method used to test soil in highway construction?

The Proctor compaction test is a widely used method for determining the optimal moisture content at which a given soil type will achieve its maximum dry density when compacted. This test is critical in highway construction because achieving the proper compaction of soil is essential for ensuring the stability and load-bearing capacity of the roadway.

During the Proctor test, soil is compacted in a mold at varying moisture contents, and the resulting density is measured. This helps engineers to identify the ideal conditions for compaction, which are necessary to avoid future roadway failures due to inadequate support or settlement.

In the context of highway construction, ensuring that the subgrade is adequately compacted can prevent issues like surface deformation, cracking, and other forms of structural damage over time, making the Proctor compaction test an invaluable tool in the construction process.

While the other tests mentioned — such as the standard penetration test, California bearing ratio test, and moisture-content test — also play significant roles in the overall assessment of soil for highway projects, the Proctor compaction test specifically addresses the efficiency of soil compaction, a key factor in the structural integrity of highways.