Question

How to calculate uniformity coefficient in soil?

Answer 1

Calculating the coefficients of uniformity and curvature requires grain diameters. The grain diameter can be found for each percent of the soil passing a particular sieve. This means that if 40% of the sample is retained on the No. 200 sieve then there is 60% passing the No. 200 sieve.[1]

The coefficient of uniformity, Cu is a crude shape parameter and is calculated using the following equation:

{\displaystyle C_{u}={\frac {D_{60}}{D_{10}}}}

where D60 is the grain diameter at 60% passing, and D10 is the grain diameter at 10% passing

The coefficient of curvature, Cc is a shape parameter and is calculated using the following equation:

{\displaystyle C_{c}={\frac {(D_{30})^{2}}{D_{10}\times \ D_{60}}}}

where D60 is the grain diameter at 60% passing, D30 is the grain diameter at 30% passing, and D10 is the grain diameter at 10% passing

Once the coefficient of uniformity and the coefficient of curvature have been calculated, they must be compared to published gradation criteria.