This test method is used to determine the relative density of cohesion less and freely draining soils, for which impact compaction will not produce a well defined moisture density curve. The maximum density produced by impact methods will generally be less than by vibratory methods. Vibratory compaction obtains maximum density with pouring, to obtain minimum density. Relative density is defined as the state of compactness of a soil with respect to the most loose and most dense states, at which it can be placed by laboratory procedures. It is expressed as the ratio of (a) the difference between the void ratio  of  a cohesion less soil in the loosest state and any given void ratio and (b) the difference between its void ratios in the most loose and most dense states. Relative density is extremely important to subsurface compaction and investigation of foundations. Building contractors and soil testing laboratories rely on this density for critical engineering designs.