The process of mechanically pressing together the particles of a soil to increase the density (compaction) is extensively employed in the construction of embankments and in strengthening the subgrades of roads and runways.
Many workers in the field talk about consolidating a soil when they really mean compacting it. Strictly speaking, consolidation is the gradual expulsion of water from the voids of a saturated cohesive soil with consequent reduction in volume, whereas compaction is the packing together of soil particles by the expulsion of air.
The densities achieved by compaction are invariably expressed as dry densities, generally in Mg/m3 although, occasionally, the units kg/m3 are used. The moisture content at which maximum dry density is obtained for a given amount of compaction is known as the optimum moisture content.
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