What Does Relative Density Mean?
The relative density or density index of soils can be defined as its state of compactness with respect to its loosest and densest possible state. It is useful in evaluating the compaction state of coarse-grained soils and also in assessing the safe bearing capacity of sandy soils.
Relative density is the ratio of the difference between the void ratio of a cohesionless soil in its loosest state (emax )and current state (e) to the difference between its void ratio in its loosest (emax )and densest state (emin)
Relative density = (emax - e)/ (emax - emin)
ASTM D4254-16 describes the standard test methods for minimum index density and unit weight of soils and calculation of relative density.
Trenchlesspedia Explains Relative Density
The relative density of a cohesionless soil sample is determined using the relative density test. The test procedure involves preparing the soil sample by drying, cooling, segregating, and sieving it.
For determining the minimum density, the dry pulverized soil is poured into a weighed mold using a spiral motion from the rim to the center. The mold is filled, leveled, and weighed.
For determining the maximum density, the empty mold is weighed, and a collar is put on its top and clamped. The oven-dried sample is filled in the mold up to 1/2 or 2/3rd of the collar.
The mold is placed on the vibrating table and fixed in place and the surcharge weight is placed on it and allowed to run for 8 minutes. The mold is weighed with the soil and weight recorded.
For determining natural density, the mold is weighed with the dry soil. The results from the above procedures are used to calculate the relative density.
The relative density gives a ratio of the actual decrease in the volume of voids in sandy soil to the maximum possible decrease in the void volume or the maximum density that the soil can attain beyond its natural state.