In case of  cohesionless soils (or soils without any fines particles), the standard compaction tests  or experiment are very much difficult to perform in the laboratory. For  necessary required compaction,  the application of mechanical  vibrations is the most scientifically  effective method. Watering process  is one of the  another method. The soil mass inside seepage force of water  which percolating through a cohesionless soil makes the soil grains  or particles to occupy a more stable and settle position. However it has been experimentally noticed that a large quantity of water is required in this experimental method. To achieve the maximum dry density level, that can be compacted either in the dry state condition or in a saturated state condition of soil mass. 

In case of these soil types, it is general to specify a magnitude value of relative density (ID) that must be achieved during the process. Now if is the current void ratio value  or gd is the current dry density value , then the relative density is usually defined as  in the  percentage as mentioned below, 


or

where as emax and emin are the maximum and minimum void ratio value and  that can be determined from standard test or experiment  in the laboratory, also gdmin and gdmax are the respective minimum and maximum dry density value as mentioned in the formula. 

On the basis of relative density value,  sands  and gravels sample can be described into different categories, which is mentioned below,  

Relative
density value (%)         Classification of soil type

       < 15               Very loose soil

      15-35              Loose soil

      35-65              Medium soil

      65-85              Dense soil

       > 85               Very dense soil

It is not always possible to determine the dry density value from the value or data  of the relative density. The actual  reason is that,  the values of the maximum and minimum dry densities (or void ratios) depend totally on the gradation system and angularity of the soil grains and particles.