Stokes law state that the terminal velocity of settling of spherical particle in suspension, various with the source of the diameter of the sphere, density & velocity of the fluid and density of the sphere.

Combines of sleve& sedimentation analysis:-

• It is done when soil mass consists of a particle of both course & fine grained soils.

• The slurry is sieved through 0.75mm is sieved.

• The material retained on the sieve is over-dired and the sieve is done using the set of fine sieves.

• The suspension passing the 75mm sieve is mixed with the deflocculating asent, if it is not done. The hydrometer test is performed.

• The % finer then any size can be calculated on the basis of origin mass of soil taken for cmbined analysis.

Uses of particles size distribution curve

1. Particle size distribution curve extremely useful for the coarse grained soils.
2. P.S.D.C - To classify the classification of coarse grained soils.
3. The coefficient of permeability of a coarse grained soils depend upon the large extend on the size of the particles.
4. The P.S.D.C - Used known as sensitivity of soil.
5. The P.S.D.C -design of drainage filters.
6. The P.S.D.C -provide index to the shear strength of soil, Generally a well graded, compacted sand has high graded soil.
7. The P.S.D.C - soil stabilization and for the design of pavement.
8. P.S.D.C -may indicates mode of deposition of soil. For EQ Gap-graded soil indicates deposition by two different agencies.

Relative Density:- The most important index aggregate property of cohensionless soil is its realative density.

The engineering properties of a mass of cohensionless soil depend upon large extend of relative density (Dr) also known as dnsity index(Io).

The relative density:- Dr=Emax-e/Emax-emin*100

Emax - Max void ratio of the soil in the loose condition. Emin- Min void ratio of the soil in theDenset condition. e Void ratio in the natural condition.