What is Compaction and Why is it Important?
Compaction is the rearrangement of soil particles to a denser state using mechanical equipment. Compaction increases the unit weight (sometimes referred to as density) of a soil by decreasing the volume of the voids in the soil structure. Compaction is important because it strengthens soil which increases the bearing capacity of a soil and decreases the settlement potential of a soil. For example, compaction of soil beneath footings for a house will decrease the overall settlement of the house. Compaction recommendations are typically given as a percentage of a soil’s maximum dry unit weight (or density) as determined by the Proctor Test. The Proctor Test (ASTM D698 & D1557) is a test that is performed in the lab on a sample of soil taken in the field. The results of the test determine the maximum unit weight (or density) and corresponding optimum moisture content for a specific soil. Once the specific soil has been compacted in the field, it is tested to determine its unit weight (or
