Question

The coefficient of curvature from the grain size distribution curve is given by:

1. \(\frac{{{D_{60}}}}{{{D_{10}}}}\)
2. \(\frac{{D_{30}^2}}{{{D_{10}}{D_{60}}}}\)
3. \(\frac{{D_{60}^2}}{{{D_{10}}{D_{30}}}}\)
4. \(\frac{{{D_{30}}}}{{{D_{10}}}}\)

Answer 1

Correct Answer - Option 2 : \(\frac{{D_{30}^2}}{{{D_{10}}{D_{60}}}}\)

Explanation:

Coefficient of Curvature / Curvature Coefficient:

\({C_c} = \frac{{D_{30}^2}}{{{D_{60}} \times {D_{10}}}}\)

For well graded soil, 1 < Cc < 3

For gap graded soil, 1 < Cc or Cc > 3

where

D60 = size at 60% finer by weight

D30 = size at 30% finer by weight

D10 = size at 10% finer by weight = Effective size

Coefficient of Uniformity / Uniformity Coefficient:

It is defined as the ratio of D60 and D10 sieve sizes in the sieve analysis of granular material.

Higher is the value of Cu larger is the range of the particle size.

\({C_u} = \frac{{{D_{60}}}}{{{D_{10}}}}\)

For uniformly graded soil, Cu = 1

For well graded sand, Cu > 6

For well graded gravel Cu > 4