What is the primary distinction between compaction and consolidation?

The primary distinction between compaction and consolidation lies in the processes they involve and the resultant effects on soil behavior and density. Compaction is a mechanical process that increases the density of soil by reducing air voids, typically through the application of external forces such as rolling or tamping. This process is important in construction to improve soil strength and load-bearing capacity.

On the other hand, consolidation refers to the gradual reduction of soil volume due to the expulsion of water from the pores in saturated soil when subjected to increased load. This is generally a time-dependent process, as it can take a significant amount of time for excess pore water pressure to dissipate and for the soil structure to stabilize.

The focus in the correct option highlights the contrasting nature of air and water removal in these two processes: compaction involves predominantly the removal of air, while consolidation involves the removal of water. This fundamental difference underpins the distinct effects of these processes on soil behavior under load.