Compaction refers to the act of compacting soil to a specified density. Normally under foundations this would be a value of 95% compaction. This can be accomplished by using big drum compactors which are usually either slick drum or sheep's foot compactors. In order for the soil to be tested, a soil sample has to be taken where the site work is being done. This sample is called a proctor. The soil sample will be tested and will provide the information needed to obtain the desired soil compaction. The soil will be tested with a nuclear testing piece of equipment. The tech will drive an iron rod in the ground in order to create a hole to push the probe into the ground and lock in place. The test will provide the soil moisture content and density. When the soil proctor was tested, it provided an optimum moisture level for the soil sample. Example: The soil might require an optimum moisture level of 12% to achieve 95% compaction. An experienced site sub can usually tell after he has added water and work the soil when the soil is ready to compact and test. Sometimes depending on the soil conditions, this might involve a few times of trial and error to obtain a good test result. Inside foundation forms plate compactors are used to achieve the required compaction. These are walk behind machines that vibrate to achieve the compaction. The moisture content still has to be correct to past the test. Another piece of compaction equipment is called a "wacky packer" or "jumping jack". This piece of equipment is used in tight places like around plumbing pipes. Each piece of compaction equipment has it's own specific need and place in the total soil compaction process.