The density of the soil, in place after compaction, varies with the soil type. It varies a small amount even site-to-site with seemingly the same soil. For that reason, there is a "standard" in the specifications that you should be required to meet. The "standard" is determined in the laboratory by taking a sample of the soil from the site and performing a moisture-density relationship. I'm not sure where you are located, but each country typically will ascribe to some defined, written standard by which the laboratory and field testing is performed. In the US, it is done by ASTM standards, in the UK by British Standards and in AU by their standards. Once the moisture density relationship is determined in the lab, a field density test is performed to determine the in place density. That in place density is then compared to the lab density to determine the percent compaction, typically required to be 95% or above for most building projects.
