Which of the following best defines soil compaction?

Soil compaction is fundamentally about reducing the volume of air in the soil and increasing the density, which directly enhances its ability to support loads. This process is typically achieved through mechanical methods such as rolling, tamping, or vibrating the soil, which rearranges the soil particles, minimizing the spaces between them. This densification is crucial for construction and engineering projects as a compacted soil layer has a higher load-bearing capacity, making it more stable for foundations, roadways, and other structures.

In contrast, simply adding water to soil, mixing different types of soils, or removing soil from its natural position does not contribute to the definition of compaction. While moisture can aid in the compaction process, it alone does not encapsulate what compaction entails. Additionally, mixing soils or relocating them can affect their properties but does not necessarily involve the densification that compaction signifies. Hence, the most accurate definition revolves around the process of densifying soil to enhance its structural integrity and load-bearing capabilities.