What is Uniformity Coefficient(Cu) And Coefficient of Curvature(Cc) of Soil

Uniformity coefficient(Cu)

The uniformity coefficient is a measure of particle size range and given by the ratio of D₆₀ and D₁₀ size of particles. It is denoted by C_u.

Thus, C_u = D₆₀/D₁₀

Where,

• D₆₀ = Size of the particle corresponding to 60% finer and,
• D₁₀ = Size of the particle corresponding to 10% finer.

Coefficient of curvature(Cc)

The coefficient of curvature is a measure of gradation of particles and given by the following expression:

C_c = (D₃₀)2/D₆₀.D₁₀

Where,

• D₆₀ = Size of the particle corresponding to 60% finer.
• D₃₀ = Size of particle corresponding to 30% finer.
• D₁₀ = Size of the particle corresponding to 10% finer.

The size D₁₀ is some times called effective size. The value of C_u is nearly equal to unity for a uniformly of poorly graded soil. The value of C_c is more than 1.0 but less than 3.0 for well-graded soil. C_u is greater than 6 for sands.

Read Also:

Pipette Method

Atterberg Limits

Sieve and Sedimentation Analysis