What effect does compaction have on unsaturated soil?

Compaction significantly affects the density and arrangement of particles in unsaturated soil by reducing the volume of air present in the voids. As soil is compacted, the particles are forced closer together, leading to a decrease in void space and, consequently, an increase in the overall density of the soil.

In an unsaturated soil condition, water fills part of the voids, while air occupies the rest. When compaction is applied, the air volume within those voids decreases as the soil particles become denser, allowing for more efficient packing of the particles. This process enhances the soil's load-bearing capacity and reduces compressibility, which is crucial for various civil engineering applications such as foundation design and slope stability.

The notion that compaction would eliminate all voids in the soil is inaccurate, as a certain amount of void space is always necessary for water movement and aeration, especially in unsaturated conditions. Additionally, the idea that compaction decreases density or increases air volume contradicts the fundamental principles of soil mechanics, which highlight that efficient compaction leads to increased density.