compaction

Compaction is a process by which the density of a material or soil increases as air voids are reduced, typically through the application of mechanical energy, moisture changes, or pressure. The goal is to produce a stable, load-bearing mass with lower porosity.

In civil engineering, soil compaction enhances bearing capacity and controls settlement. Field compaction uses rollers, rammers, or vibro-tools; laboratory tests, such as the Standard and Modified Proctor tests, determine the maximum dry density and optimum moisture content for a given soil. Factors include soil type, moisture, and compaction energy. Proper compaction improves stability and reduces later settlement, but over-compaction can decrease permeability and cause other undesirable effects.

Natural compaction occurs when overlying sediment applies pressure that rearranges grains and reduces porosity, transforming loose sediments into compacted layers or sedimentary rocks. This process also decreases porosity and permeability in groundwater reservoirs, affecting aquifers and the movement of fluids.

In manufacturing, powder compaction forms solid parts by pressing powders into a die. Dry or wet pressing may be used, often with binders. The compacted “green body” is then sintered to promote bonding and achieve higher strength and density, a common route in ceramics and metal parts production.

Common performance measures include density, porosity, permeability, and mechanical strength. Compaction control is important to avoid under-compaction, which weakens the material, or over-compaction, which can reduce drainage, induce cracks, or create excessive stiffness in soils and road subbases. See also soil mechanics and powder metallurgy.