What is compaction?

• A. The process used to achieve density, the product
• B. The density of soil after rain
• C. The method for testing bearing capacity
• D. The measured water content of material

Answer: (A)

Compaction is the process of densifying soil by applying mechanical energy to reduce air voids, which increases the material’s density. The result is compacted soil with higher dry density and improved load-bearing capacity, making it suitable for subgrades and road bases. This process relies on moisture content—there’s an optimum moisture level at which the soil reaches maximum dry density when compacted. It’s not simply the density you see after rain, nor a method for testing bearing capacity, nor a measurement of water content. Those are separate ideas; compaction specifically describes the act of densifying the soil and the dense state that results from it.