Particle Size Distribution Curve | Properties of Soil | Soil Mechanics

  Particle Size Distribution Curve  

• The result of the particle size distribution analysis is reported in the form of a curve termed as particle size distribution curve, in which % finer is expressed on the Y-axis &size of a particle is expressed on X-axis on a log scale.
• This curve helps in analyzing the type of soil & gradation of soil.
• The soil may be termed well-graded soil. If it has a good representation of all sizes of particle in it.

• It soil consist of excess of one size particle & deficiency of another size of particle ( or it consist  of the particle of same size ) it is termed poorly graded soil (in later case it is termed as Uniformly Graded Soil).

• It certain size of particle are missing from soil it is termed as gap/flat graded soil.

Particle Size Distribution Curve

For Coarse Grained soil D10, D30, and D60 size of particle holds higher significance & can be found using the particle size distribution curve.

• D10= Size in (mm) such that 10% of particles are finer than this size. It is also termed as efficiency size or effective diameter as defined “By Allen Hagen “.
• D30= Size in (mm) such that 60% of particles are finer than this size.
• D60= Size in (mm) such that 60% of particles are finer than this size.

Their significance is more as this size helps in finding the gradation of Coarse-Grained soil in terms of the following parameters.

Coefficient of Uniformly (Cu)

It represents particle size range of distribution curve.

It is defined as ratio of D60 size of particles to the D10 size of particles.

\(Cc=\frac{D_{60}}{D_{10}}\) 

For uniformly graded soil, Cu, = 1 (or less than 2)

For well graded sand, Cu, > 6.

For well graded Gravel, Cu, > 4

Coefficient of Curvature (Cc)

If represents shape of particle size distribution curve.

It is defined as

\(Cc=\frac{D_{30}^{2}}{D_{60}·D_{10}}\) 

For well-graded soil, Cc should be in the range of 1 to 3

If Cc, is less than 1 or greater than 3, then the soil is gap-graded soil.

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