The relative density of cohesionless soil is an essential tool for determining the compactness of free-draining soils, especially in building and engineering applications. It determines the soil's stability and load-bearing capacity, which ensures optimum foundation and building support. The apparatus aims to determine the maximum dry density and water content (humidity/density ratio) of cohesionless mixtures, with the vibratory approach yielding greater density than the impact method.

Relative density is the ratio of the difference between the void ratios in the loosest and natural state (emax - e) to the difference between the loosest and densest state (emax - emin). This calculation is essential to define the compactness and stability of the cohesionless soil.

This method is applicable for materials containing up to 12% fines (particles smaller than 0.063 mm) by mass, with a maximum particle size of 80 mm. It is particularly useful for determining the relative density of cohesionless soils, such as sand and gravel, which are free-draining and do not respond well to traditional moisture-density compaction tests. The vibratory compaction method is used to achieve the maximum density, while pouring is used to determine the minimum density.