Relative Density of Soil

1. objective

Porosity of a soil depends on the shape of grain, uniformity of grain size and condition of sedimentation. Hence porosity itself does not indicate whether a soil is in loose or dense state. This information can only be obtained by comparing the porosity or void ratio of the given soil with that of the same soil in its loosest and densest possible state and hence the term, relative density is introduced.

Relative density is the measure of compactness of cohesionless soil. Relative density or density index is the ratio of the difference between the void ratios of a cohesionless soil in its loosest state and existing natural state to the difference between its void ratio in the loosest and densest states.

Determination of relative density is helpful in evaluating compaction state of coarse grained soils and also assessing the safe bearing capacity in case of sandy soils.

Relative Density = (emax - e)/ (emax - emin)


We have,


e = {G YW/Yd} - 1

So, "e" is inversely proportional to "Yd"

2. apparatus required


Fig. 1: Relative Density Apparatus

The Apparatus consists of (a) Cushioned steel vibrating deck 75X75 cm size, R.P.M : 3600 ; under a net mass of over 45 kg. (b) Two cylindrical metallic moulds, 3000 cc and 15000 cc conforming to requirements given in IS : 10837-1984. (c) 10 mm thick surcharge base plate with handle separately for each mould. (d) Surcharge weights, one for each size having a weight equal to 140 gms / conforming to requirements given in IS : 10837-1984. (e) Guide sleeves with clamps for each mould separately. (f) Calibration bar 75X300X3 mm.

Fig. 2: Mixing Pan

Suitable size are 60 x 90 cm and 10 cm deep and 40 x 40 cm and 5 cm deep.

Fig. 3: Weighing Scale

Portable platform scale, 100 kg capacity with sensitivity of 20 g in accordance with IS:1435-l960.

3. reference

IS 2720(Part 14):1983 Methods of test for soils: Determination of density Index (Relative Density) of Cohesionless Soil (First revision). Reaffirmed- Dec 2015.

4. procedure