What is soil compaction and why is it important?

Soil compaction is the densification of soil by mechanical means to reduce air voids, increasing density and strength. It improves bearing capacity, reduces permeability, minimizes settlement, and increases slope stability. Key parameters include maximum dry density and optimum moisture content (from Proctor test). Field compaction uses rollers (smooth, sheepsfoot, vibratory) depending on soil type. Quality control uses nuclear density gauge or sand cone test to verify achieving specified relative compaction (typically 95%).