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 e 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,
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,
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.