Soil Compaction Testing
In geotechnical engineering, soil compaction is the process in which a stress applied to a soil causes densification as air is displaced from the pores between the soil grains. When stress is applied that causes densification due to water (or other liquid) being displaced from between the soil grains then consolidation, not compaction, has occurred. Normally, compaction is the result of heavy machinery compressing the soil, but it can also occur due to the passage of equipment or heavy materials.
The soil type, such as grain-size distributions, shape of the soil grains, specific gravity of soil solids, and percentage and type of clay minerals in a soil has a great influence on the maximum dry unit weight and optimum moisture content. It also has a great influence on how the materials should be compacted in given situations. Compaction is accomplished by use of heavy equipment. In sands and gravels, the equipment usually vibrates, to cause re-orientation of the soil particles into a denser configuration. In silts and clays, a sheepsfoot roller is frequently used, to create small zones of intense shearing, which drives air out of the soil.
Per CBC, field density testing must be provided wherever the soil density is less than 90 percent of the relative compaction. In order to verify the relative degree of compaction a nuclear gauge density testing tool drive, tube knocker and /or sand cone tools can be used. Heavy grading equipment is usually are used to compact the overexcavated soils.
To determine the maximum dry density and optimum moisture content of each major soil type encountered during a grading, laboratory testing using ASTM Method D-1557-00 should be employed.